aboutsummaryrefslogtreecommitdiff
path: root/gcc/ada/5qtaprop.adb
blob: a487d5dce40e362a51278b158a1480d6ba9193e5 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
------------------------------------------------------------------------------
--                                                                          --
--                GNU ADA RUN-TIME LIBRARY (GNARL) COMPONENTS               --
--                                                                          --
--     S Y S T E M . T A S K _ P R I M I T I V E S . O P E R A T I O N S    --
--                                                                          --
--                                  B o d y                                 --
--                                                                          --
--                             $Revision$
--                                                                          --
--             Copyright (C) 1991-2001, Florida State University            --
--                                                                          --
-- GNARL is free software; you can  redistribute it  and/or modify it under --
-- terms of the  GNU General Public License as published  by the Free Soft- --
-- ware  Foundation;  either version 2,  or (at your option) any later ver- --
-- sion. GNARL is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
-- for  more details.  You should have  received  a copy of the GNU General --
-- Public License  distributed with GNARL; see file COPYING.  If not, write --
-- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
-- MA 02111-1307, USA.                                                      --
--                                                                          --
-- As a special exception,  if other files  instantiate  generics from this --
-- unit, or you link  this unit with other files  to produce an executable, --
-- this  unit  does not  by itself cause  the resulting  executable  to  be --
-- covered  by the  GNU  General  Public  License.  This exception does not --
-- however invalidate  any other reasons why  the executable file  might be --
-- covered by the  GNU Public License.                                      --
--                                                                          --
-- GNARL was developed by the GNARL team at Florida State University. It is --
-- now maintained by Ada Core Technologies Inc. in cooperation with Florida --
-- State University (http://www.gnat.com).                                  --
--                                                                          --
------------------------------------------------------------------------------

--  RT GNU/Linux version

--  ???? Later, look at what we might want to provide for interrupt
--  management.

pragma Suppress (All_Checks);

pragma Polling (Off);
--  Turn off polling, we do not want ATC polling to take place during
--  tasking operations. It causes infinite loops and other problems.

with System.Machine_Code;
--  used for Asm

with System.OS_Interface;
--  used for various types, constants, and operations

with System.OS_Primitives;
--  used for Delay_Modes

with System.Parameters;
--  used for Size_Type

with System.Storage_Elements;

with System.Tasking;
--  used for Ada_Task_Control_Block
--           Task_ID

with Ada.Unchecked_Conversion;

package body System.Task_Primitives.Operations is

   use System.Machine_Code,
       System.OS_Interface,
       System.OS_Primitives,
       System.Parameters,
       System.Tasking,
       System.Storage_Elements;

   --------------------------------
   -- RT GNU/Linux specific Data --
   --------------------------------

   --  Define two important parameters necessary for a GNU/Linux kernel module.
   --  Any module that is going to be loaded into the kernel space needs these
   --  parameters.

   Mod_Use_Count : Integer;
   pragma Export (C, Mod_Use_Count, "mod_use_count_");
   --  for module usage tracking by the kernel

   type Aliased_String is array (Positive range <>) of aliased Character;
   pragma Convention (C, Aliased_String);

   Kernel_Version : constant Aliased_String := "2.0.33" & ASCII.Nul;
   pragma Export (C, Kernel_Version, "kernel_version");
   --  So that insmod can find the version number.

   --  The following procedures have their name specified by the GNU/Linux
   --  module loader. Note that they simply correspond to adainit/adafinal.

   function Init_Module return Integer;
   pragma Export (C, Init_Module, "init_module");

   procedure Cleanup_Module;
   pragma Export (C, Cleanup_Module, "cleanup_module");

   ----------------
   -- Local Data --
   ----------------

   LF   : constant String := ASCII.LF & ASCII.Nul;

   LFHT : constant String := ASCII.LF & ASCII.HT;
   --  used in inserted assembly code

   Max_Tasks : constant := 10;
   --  ??? Eventually, this should probably be in System.Parameters.

   Known_Tasks : array (0 .. Max_Tasks) of Task_ID;
   --  Global array of tasks read by gdb, and updated by Create_Task and
   --  Finalize_TCB. It's from System.Tasking.Debug. We moved it here to
   --  cut the dependence on that package. Consider moving it here or to
   --  this package specification, permanently????

   Max_Sensible_Delay : constant RTIME :=
     365 * 24 * 60 * 60 * RT_TICKS_PER_SEC;
   --  Max of one year delay, needed to prevent exceptions for large
   --  delay values. It seems unlikely that any test will notice this
   --  restriction.
   --  ??? This is really declared in System.OS_Primitives,
   --  and the type is Duration, here its type is RTIME.

   Tick_Count : constant := RT_TICKS_PER_SEC / 20;
   Nano_Count : constant := 50_000_000;
   --  two constants used in conversions between RTIME and Duration.

   Addr_Bytes : constant Storage_Offset :=
     System.Address'Max_Size_In_Storage_Elements;
   --  number of bytes needed for storing an address.

   Guess : constant RTIME := 10;
   --  an approximate amount of RTIME used in scheduler to awake a task having
   --  its resume time within 'current time + Guess'
   --  The value of 10 is estimated here and may need further refinement

   TCB_Array : array (0 .. Max_Tasks)
     of aliased Restricted_Ada_Task_Control_Block (Entry_Num => 0);
   pragma Volatile_Components (TCB_Array);

   Available_TCBs : Task_ID;
   pragma Atomic (Available_TCBs);
   --  Head of linear linked list of available TCB's, linked using TCB's
   --  LL.Next. This list is Initialized to contain a fixed number of tasks,
   --  when the runtime system starts up.

   Current_Task : Task_ID;
   pragma Export (C, Current_Task, "current_task");
   pragma Atomic (Current_Task);
   --  This is the task currently running. We need the pragma here to specify
   --  the link-name for Current_Task is "current_task", rather than the long
   --  name (including the package name) that the Ada compiler would normally
   --  generate. "current_task" is referenced in procedure Rt_Switch_To below

   Idle_Task : aliased Restricted_Ada_Task_Control_Block (Entry_Num => 0);
   --  Tail of the circular queue of ready to run tasks.

   Scheduler_Idle : Boolean := False;
   --  True when the scheduler is idle (no task other than the idle task
   --  is on the ready queue).

   In_Elab_Code : Boolean := True;
   --  True when we are elaborating our application.
   --  Init_Module will set this flag to false and never revert it.

   Timer_Queue : aliased Restricted_Ada_Task_Control_Block (Entry_Num => 0);
   --  Header of the queue of delayed real-time tasks.
   --  Timer_Queue.LL has to be initialized properly before being used

   Timer_Expired : Boolean := False;
   --  flag to show whether the Timer_Queue needs to be checked
   --  when it becomes true, it means there is a task in the
   --  Timer_Queue having to be awakened and be moved to ready queue

   Environment_Task_ID : Task_ID;
   --  A variable to hold Task_ID for the environment task.
   --  Once initialized, this behaves as a constant.
   --  In the current implementation, this is the task assigned permanently
   --  as the regular GNU/Linux kernel.

   All_Tasks_L : aliased RTS_Lock;
   --  See comments on locking rules in System.Tasking (spec).

   --  The followings are internal configuration constants needed.
   Next_Serial_Number : Task_Serial_Number := 100;
   pragma Volatile (Next_Serial_Number);
   --  We start at 100, to reserve some special values for
   --  using in error checking.

   GNU_Linux_Irq_State : Integer := 0;
   --  This needs comments ???

   type Duration_As_Integer is delta 1.0
      range -2.0**(Duration'Size - 1) .. 2.0**(Duration'Size - 1) - 1.0;
   --  used for output RTIME value during debugging

   type Address_Ptr is access all System.Address;
   pragma Convention (C, Address_Ptr);

   --------------------------------
   -- Local conversion functions --
   --------------------------------

   function To_Task_ID is new
     Ada.Unchecked_Conversion (System.Address, Task_ID);

   function To_Address is new
     Ada.Unchecked_Conversion (Task_ID, System.Address);

   function RTIME_To_D_Int is new
     Ada.Unchecked_Conversion (RTIME, Duration_As_Integer);

   function Raw_RTIME is new
     Ada.Unchecked_Conversion (Duration, RTIME);

   function Raw_Duration is new
     Ada.Unchecked_Conversion (RTIME, Duration);

   function To_Duration (T : RTIME) return Duration;
   pragma Inline (To_Duration);

   function To_RTIME (D : Duration) return RTIME;
   pragma Inline (To_RTIME);

   function To_Integer is new
     Ada.Unchecked_Conversion (System.Parameters.Size_Type, Integer);

   function To_Address_Ptr is
     new Ada.Unchecked_Conversion (System.Address, Address_Ptr);

   function To_RTS_Lock_Ptr is new
     Ada.Unchecked_Conversion (Lock_Ptr, RTS_Lock_Ptr);

   -----------------------------------
   -- Local Subprogram Declarations --
   -----------------------------------

   procedure Rt_Switch_To (Tsk : Task_ID);
   pragma Inline (Rt_Switch_To);
   --  switch from the 'current_task' to 'Tsk'
   --  and 'Tsk' then becomes 'current_task'

   procedure R_Save_Flags (F : out Integer);
   pragma Inline (R_Save_Flags);
   --  save EFLAGS register to 'F'

   procedure R_Restore_Flags (F : Integer);
   pragma Inline (R_Restore_Flags);
   --  restore EFLAGS register from 'F'

   procedure R_Cli;
   pragma Inline (R_Cli);
   --  disable interrupts

   procedure R_Sti;
   pragma Inline (R_Sti);
   --  enable interrupts

   procedure Timer_Wrapper;
   --  the timer handler. It sets Timer_Expired flag to True and
   --  then calls Rt_Schedule

   procedure Rt_Schedule;
   --  the scheduler

   procedure Insert_R (T : Task_ID);
   pragma Inline (Insert_R);
   --  insert 'T' into the tail of the ready queue for its active
   --  priority
   --  if original queue is 6 5 4 4 3 2 and T has priority of 4
   --  then after T is inserted the queue becomes 6 5 4 4 T 3 2

   procedure Insert_RF (T : Task_ID);
   pragma Inline (Insert_RF);
   --  insert 'T' into the front of the ready queue for its active
   --  priority
   --  if original queue is 6 5 4 4 3 2 and T has priority of 4
   --  then after T is inserted the queue becomes 6 5 T 4 4 3 2

   procedure Delete_R (T : Task_ID);
   pragma Inline (Delete_R);
   --  delete 'T' from the ready queue. If 'T' is not in any queue
   --  the operation has no effect

   procedure Insert_T (T : Task_ID);
   pragma Inline (Insert_T);
   --  insert 'T' into the waiting queue according to its Resume_Time.
   --  If there are tasks in the waiting queue that have the same
   --  Resume_Time as 'T', 'T' is then inserted into the queue for
   --  its active priority

   procedure Delete_T (T : Task_ID);
   pragma Inline (Delete_T);
   --  delete 'T' from the waiting queue.

   procedure Move_Top_Task_From_Timer_Queue_To_Ready_Queue;
   pragma Inline (Move_Top_Task_From_Timer_Queue_To_Ready_Queue);
   --  remove the task in the front of the waiting queue and insert it
   --  into the tail of the ready queue for its active priority

   -------------------------
   --  Local Subprograms  --
   -------------------------

   procedure Rt_Switch_To (Tsk : Task_ID) is
   begin
      pragma Debug (Printk ("procedure Rt_Switch_To called" & LF));

      Asm (
        "pushl %%eax" & LFHT &
        "pushl %%ebp" & LFHT &
        "pushl %%edi" & LFHT &
        "pushl %%esi" & LFHT &
        "pushl %%edx" & LFHT &
        "pushl %%ecx" & LFHT &
        "pushl %%ebx" & LFHT &

        "movl current_task, %%edx" & LFHT &
        "cmpl $0, 36(%%edx)" & LFHT &
         --  36 is hard-coded, 36(%%edx) is actually
         --  Current_Task.Common.LL.Uses_Fp

        "jz 25f" & LFHT &
        "sub $108,%%esp" & LFHT &
        "fsave (%%esp)" & LFHT &
        "25:      pushl $1f" & LFHT &
        "movl %%esp, 32(%%edx)" & LFHT &
         --  32 is hard-coded, 32(%%edx) is actually
         --  Current_Task.Common.LL.Stack

        "movl 32(%%ecx), %%esp" & LFHT &
         --  32 is hard-coded, 32(%%ecx) is actually Tsk.Common.LL.Stack.
         --  Tsk is the task to be switched to

        "movl %%ecx, current_task" & LFHT &
        "ret" & LFHT &
        "1:       cmpl $0, 36(%%ecx)" & LFHT &
         --  36(%%exc) is Tsk.Common.LL.Stack (hard coded)
        "jz 26f" & LFHT &
        "frstor (%%esp)" & LFHT &
        "add $108,%%esp" & LFHT &
        "26:      popl %%ebx" & LFHT &
        "popl %%ecx" & LFHT &
        "popl %%edx" & LFHT &
        "popl %%esi" & LFHT &
        "popl %%edi" & LFHT &
        "popl %%ebp" & LFHT &
        "popl %%eax",
        Outputs  => No_Output_Operands,
        Inputs   => Task_ID'Asm_Input ("c", Tsk),
        Clobber  => "cx",
        Volatile => True);
   end Rt_Switch_To;

   procedure R_Save_Flags (F : out Integer) is
   begin
      Asm (
        "pushfl" & LFHT &
        "popl %0",
        Outputs  => Integer'Asm_Output ("=g", F),
        Inputs   => No_Input_Operands,
        Clobber  => "memory",
        Volatile => True);
   end R_Save_Flags;

   procedure R_Restore_Flags (F : Integer) is
   begin
      Asm (
        "pushl %0" & LFHT &
        "popfl",
        Outputs  => No_Output_Operands,
        Inputs   => Integer'Asm_Input ("g", F),
        Clobber  => "memory",
        Volatile => True);
   end R_Restore_Flags;

   procedure R_Sti is
   begin
      Asm (
         "sti",
         Outputs  => No_Output_Operands,
         Inputs   => No_Input_Operands,
         Clobber  => "memory",
         Volatile => True);
   end R_Sti;

   procedure R_Cli is
   begin
      Asm (
        "cli",
        Outputs  => No_Output_Operands,
        Inputs   => No_Input_Operands,
        Clobber  => "memory",
        Volatile => True);
   end R_Cli;

   --  A wrapper for Rt_Schedule, works as the timer handler

   procedure Timer_Wrapper is
   begin
      pragma Debug (Printk ("procedure Timer_Wrapper called" & LF));

      Timer_Expired := True;
      Rt_Schedule;
   end Timer_Wrapper;

   procedure Rt_Schedule is
      Now      : RTIME;
      Top_Task : Task_ID;
      Flags    : Integer;

      procedure Debug_Timer_Queue;
      --  Check the state of the Timer Queue.

      procedure Debug_Timer_Queue is
      begin
         if Timer_Queue.Common.LL.Succ /= Timer_Queue'Address then
            Printk ("Timer_Queue not empty" & LF);
         end if;

         if To_Task_ID (Timer_Queue.Common.LL.Succ).Common.LL.Resume_Time <
           Now + Guess
         then
            Printk ("and need to move top task to ready queue" & LF);
         end if;
      end Debug_Timer_Queue;

   begin
      pragma Debug (Printk ("procedure Rt_Schedule called" & LF));

      --  Scheduler_Idle means that this call comes from an interrupt
      --  handler (e.g timer) that interrupted the idle loop below.

      if Scheduler_Idle then
         return;
      end if;

      <<Idle>>
      R_Save_Flags (Flags);
      R_Cli;

      Scheduler_Idle := False;

      if Timer_Expired then
         pragma Debug (Printk ("Timer expired" & LF));
         Timer_Expired := False;

         --  Check for expired time delays.
         Now := Rt_Get_Time;

         --  Need another (circular) queue for delayed tasks, this one ordered
         --  by wakeup time, so the one at the front has the earliest resume
         --  time. Wake up all the tasks sleeping on time delays that should
         --  be awakened at this time.

         --  ??? This is not very good, since we may waste time here waking
         --  up a bunch of lower priority tasks, adding to the blocking time
         --  of higher priority ready tasks, but we don't see how to get
         --  around this without adding more wasted time elsewhere.

         pragma Debug (Debug_Timer_Queue);

         while Timer_Queue.Common.LL.Succ /= Timer_Queue'Address and then
           To_Task_ID
             (Timer_Queue.Common.LL.Succ).Common.LL.Resume_Time < Now + Guess
         loop
            To_Task_ID (Timer_Queue.Common.LL.Succ).Common.LL.State :=
              RT_TASK_READY;
            Move_Top_Task_From_Timer_Queue_To_Ready_Queue;
         end loop;

         --  Arm the timer if necessary.
         --  ??? This may be wasteful, if the tasks on the timer queue are
         --  of lower priority than the current task's priority. The problem
         --  is that we can't tell this without scanning the whole timer
         --  queue. This scanning takes extra time.

         if Timer_Queue.Common.LL.Succ /= Timer_Queue'Address then
            --  Timer_Queue is not empty, so set the timer to interrupt at
            --  the next resume time. The Wakeup procedure must also do this,
            --  and must do it while interrupts are disabled so that there is
            --  no danger of interleaving with this code.
            Rt_Set_Timer
              (To_Task_ID (Timer_Queue.Common.LL.Succ).Common.LL.Resume_Time);
         else
            Rt_No_Timer;
         end if;
      end if;

      Top_Task := To_Task_ID (Idle_Task.Common.LL.Succ);

      --  If the ready queue is empty, the kernel has to wait until the timer
      --  or another interrupt makes a task ready.

      if Top_Task = To_Task_ID (Idle_Task'Address) then
         Scheduler_Idle := True;
         R_Restore_Flags (Flags);
         pragma Debug (Printk ("!!!kernel idle!!!" & LF));
         goto Idle;
      end if;

      if Top_Task = Current_Task then
         pragma Debug (Printk ("Rt_Schedule: Top_Task = Current_Task" & LF));
         --  if current task continues, just return.

         R_Restore_Flags (Flags);
         return;
      end if;

      if Top_Task = Environment_Task_ID then
         pragma Debug (Printk
           ("Rt_Schedule: Top_Task = Environment_Task" & LF));
         --  If there are no RT tasks ready, we execute the regular
         --  GNU/Linux kernel, and allow the regular GNU/Linux interrupt
         --  handlers to preempt the current task again.

         if not In_Elab_Code then
            SFIF := GNU_Linux_Irq_State;
         end if;

      elsif Current_Task = Environment_Task_ID then
         pragma Debug (Printk
           ("Rt_Schedule: Current_Task = Environment_Task" & LF));
         --  We are going to preempt the regular GNU/Linux kernel to
         --  execute an RT task, so don't allow the regular GNU/Linux
         --  interrupt handlers to preempt the current task any more.

         GNU_Linux_Irq_State := SFIF;
         SFIF := 0;
      end if;

      Top_Task.Common.LL.State := RT_TASK_READY;
      Rt_Switch_To (Top_Task);
      R_Restore_Flags (Flags);
   end Rt_Schedule;

   procedure Insert_R (T : Task_ID) is
      Q : Task_ID := To_Task_ID (Idle_Task.Common.LL.Succ);
   begin
      pragma Debug (Printk ("procedure Insert_R called" & LF));

      pragma Assert (T.Common.LL.Succ = To_Address (T));
      pragma Assert (T.Common.LL.Pred = To_Address (T));

      --  T is inserted in the queue between a task that has higher
      --  or the same Active_Priority as T and a task that has lower
      --  Active_Priority than T

      while Q /= To_Task_ID (Idle_Task'Address)
        and then T.Common.LL.Active_Priority <= Q.Common.LL.Active_Priority
      loop
         Q := To_Task_ID (Q.Common.LL.Succ);
      end loop;

      --  Q is successor of T

      T.Common.LL.Succ := To_Address (Q);
      T.Common.LL.Pred := Q.Common.LL.Pred;
      To_Task_ID (T.Common.LL.Pred).Common.LL.Succ := To_Address (T);
      Q.Common.LL.Pred := To_Address (T);
   end Insert_R;

   procedure Insert_RF (T : Task_ID) is
      Q : Task_ID := To_Task_ID (Idle_Task.Common.LL.Succ);
   begin
      pragma Debug (Printk ("procedure Insert_RF called" & LF));

      pragma Assert (T.Common.LL.Succ = To_Address (T));
      pragma Assert (T.Common.LL.Pred = To_Address (T));

      --  T is inserted in the queue between a task that has higher
      --  Active_Priority as T and a task that has lower or the same
      --  Active_Priority as T

      while Q /= To_Task_ID (Idle_Task'Address) and then
        T.Common.LL.Active_Priority < Q.Common.LL.Active_Priority
      loop
         Q := To_Task_ID (Q.Common.LL.Succ);
      end loop;

      --  Q is successor of T

      T.Common.LL.Succ := To_Address (Q);
      T.Common.LL.Pred := Q.Common.LL.Pred;
      To_Task_ID (T.Common.LL.Pred).Common.LL.Succ := To_Address (T);
      Q.Common.LL.Pred := To_Address (T);
   end Insert_RF;

   procedure Delete_R (T : Task_ID) is
      Tpred : constant Task_ID := To_Task_ID (T.Common.LL.Pred);
      Tsucc : constant Task_ID := To_Task_ID (T.Common.LL.Succ);

   begin
      pragma Debug (Printk ("procedure Delete_R called" & LF));

      --  checking whether T is in the queue is not necessary because
      --  if T is not in the queue, following statements changes
      --  nothing. But T cannot be in the Timer_Queue, otherwise
      --  activate the check below, note that checking whether T is
      --  in a queue is a relatively expensive operation

      Tpred.Common.LL.Succ := To_Address (Tsucc);
      Tsucc.Common.LL.Pred := To_Address (Tpred);
      T.Common.LL.Succ := To_Address (T);
      T.Common.LL.Pred := To_Address (T);
   end Delete_R;

   procedure Insert_T (T : Task_ID) is
      Q : Task_ID := To_Task_ID (Timer_Queue.Common.LL.Succ);
   begin
      pragma Debug (Printk ("procedure Insert_T called" & LF));

      pragma Assert (T.Common.LL.Succ = To_Address (T));

      while Q /= To_Task_ID (Timer_Queue'Address) and then
        T.Common.LL.Resume_Time > Q.Common.LL.Resume_Time
      loop
         Q := To_Task_ID (Q.Common.LL.Succ);
      end loop;

      --  Q is the task that has Resume_Time equal to or greater than that
      --  of T. If they have the same Resume_Time, continue looking for the
      --  location T is to be inserted using its Active_Priority

      while Q /= To_Task_ID (Timer_Queue'Address) and then
        T.Common.LL.Resume_Time = Q.Common.LL.Resume_Time
      loop
         exit when T.Common.LL.Active_Priority > Q.Common.LL.Active_Priority;
         Q := To_Task_ID (Q.Common.LL.Succ);
      end loop;

      --  Q is successor of T

      T.Common.LL.Succ := To_Address (Q);
      T.Common.LL.Pred := Q.Common.LL.Pred;
      To_Task_ID (T.Common.LL.Pred).Common.LL.Succ := To_Address (T);
      Q.Common.LL.Pred := To_Address (T);
   end Insert_T;

   procedure Delete_T (T : Task_ID) is
      Tpred : constant Task_ID := To_Task_ID (T.Common.LL.Pred);
      Tsucc : constant Task_ID := To_Task_ID (T.Common.LL.Succ);

   begin
      pragma Debug (Printk ("procedure Delete_T called" & LF));

      pragma Assert (T /= To_Task_ID (Timer_Queue'Address));

      Tpred.Common.LL.Succ := To_Address (Tsucc);
      Tsucc.Common.LL.Pred := To_Address (Tpred);
      T.Common.LL.Succ := To_Address (T);
      T.Common.LL.Pred := To_Address (T);
   end Delete_T;

   procedure Move_Top_Task_From_Timer_Queue_To_Ready_Queue is
      Top_Task : Task_ID := To_Task_ID (Timer_Queue.Common.LL.Succ);
   begin
      pragma Debug (Printk ("procedure Move_Top_Task called" & LF));

      if Top_Task /= To_Task_ID (Timer_Queue'Address) then
         Delete_T (Top_Task);
         Top_Task.Common.LL.State := RT_TASK_READY;
         Insert_R (Top_Task);
      end if;
   end  Move_Top_Task_From_Timer_Queue_To_Ready_Queue;

   ----------
   -- Self --
   ----------

   function Self return Task_ID is
   begin
      pragma Debug (Printk ("function Self called" & LF));

      return Current_Task;
   end Self;

   ---------------------
   -- Initialize_Lock --
   ---------------------

   procedure Initialize_Lock (Prio : System.Any_Priority; L : access Lock) is
   begin
      pragma Debug (Printk ("procedure Initialize_Lock called" & LF));

      L.Ceiling_Priority := Prio;
      L.Owner := System.Null_Address;
   end Initialize_Lock;

   procedure Initialize_Lock (L : access RTS_Lock; Level : Lock_Level) is
   begin
      pragma Debug (Printk ("procedure Initialize_Lock (RTS) called" & LF));

      L.Ceiling_Priority := System.Any_Priority'Last;
      L.Owner := System.Null_Address;
   end Initialize_Lock;

   -------------------
   -- Finalize_Lock --
   -------------------

   procedure Finalize_Lock (L : access Lock) is
   begin
      pragma Debug (Printk ("procedure Finalize_Lock called" & LF));
      null;
   end Finalize_Lock;

   procedure Finalize_Lock (L : access RTS_Lock) is
   begin
      pragma Debug (Printk ("procedure Finalize_Lock (RTS) called" & LF));
      null;
   end Finalize_Lock;

   ----------------
   -- Write_Lock --
   ----------------

   procedure Write_Lock
     (L : access Lock;
      Ceiling_Violation : out Boolean)
   is
      Prio : constant System.Any_Priority :=
        Current_Task.Common.LL.Active_Priority;
   begin
      pragma Debug (Printk ("procedure Write_Lock called" & LF));

      Ceiling_Violation := False;

      if Prio > L.Ceiling_Priority then
         --  Ceiling violation.
         --  This should never happen, unless something is seriously
         --  wrong with task T or the entire run-time system.
         --  ???? extreme error recovery, e.g. shut down the system or task

         Ceiling_Violation := True;
         pragma Debug (Printk ("Ceiling Violation in Write_Lock" & LF));
         return;
      end if;

      L.Pre_Locking_Priority := Prio;
      L.Owner := To_Address (Current_Task);
      Current_Task.Common.LL.Active_Priority := L.Ceiling_Priority;

      if Current_Task.Common.LL.Outer_Lock = null then
         --  If this lock is not nested, record a pointer to it.

         Current_Task.Common.LL.Outer_Lock :=
           To_RTS_Lock_Ptr (L.all'Unchecked_Access);
      end if;
   end Write_Lock;

   procedure Write_Lock (L : access RTS_Lock) is
      Prio : constant System.Any_Priority :=
        Current_Task.Common.LL.Active_Priority;

   begin
      pragma Debug (Printk ("procedure Write_Lock (RTS) called" & LF));

      if Prio > L.Ceiling_Priority then
         --  Ceiling violation.
         --  This should never happen, unless something is seriously
         --  wrong with task T or the entire runtime system.
         --  ???? extreme error recovery, e.g. shut down the system or task

         Printk ("Ceiling Violation in Write_Lock (RTS)" & LF);
         return;
      end if;

      L.Pre_Locking_Priority := Prio;
      L.Owner := To_Address (Current_Task);
      Current_Task.Common.LL.Active_Priority := L.Ceiling_Priority;

      if Current_Task.Common.LL.Outer_Lock = null then
         Current_Task.Common.LL.Outer_Lock := L.all'Unchecked_Access;
      end if;
   end Write_Lock;

   procedure Write_Lock (T : Task_ID) is
      Prio : constant System.Any_Priority :=
        Current_Task.Common.LL.Active_Priority;

   begin
      pragma Debug (Printk ("procedure Write_Lock (Task_ID) called" & LF));

      if Prio > T.Common.LL.L.Ceiling_Priority then
         --  Ceiling violation.
         --  This should never happen, unless something is seriously
         --  wrong with task T or the entire runtime system.
         --  ???? extreme error recovery, e.g. shut down the system or task

         Printk ("Ceiling Violation in Write_Lock (Task)" & LF);
         return;
      end if;

      T.Common.LL.L.Pre_Locking_Priority := Prio;
      T.Common.LL.L.Owner := To_Address (Current_Task);
      Current_Task.Common.LL.Active_Priority := T.Common.LL.L.Ceiling_Priority;

      if Current_Task.Common.LL.Outer_Lock = null then
         Current_Task.Common.LL.Outer_Lock := T.Common.LL.L'Access;
      end if;
   end Write_Lock;

   ---------------
   -- Read_Lock --
   ---------------

   procedure Read_Lock (L : access Lock; Ceiling_Violation : out Boolean) is
   begin
      pragma Debug (Printk ("procedure Read_Lock called" & LF));
      Write_Lock (L, Ceiling_Violation);
   end Read_Lock;

   ------------
   -- Unlock --
   ------------

   procedure Unlock (L : access Lock) is
      Flags : Integer;
   begin
      pragma Debug (Printk ("procedure Unlock called" & LF));

      if L.Owner /= To_Address (Current_Task) then
         --  ...error recovery

         null;
         Printk ("The caller is not the owner of the lock" & LF);
         return;
      end if;

      L.Owner := System.Null_Address;

      --  Now that the lock is released, lower own priority,

      if Current_Task.Common.LL.Outer_Lock =
        To_RTS_Lock_Ptr (L.all'Unchecked_Access)
      then
         --  This lock is the outer-most one, reset own priority to
         --  Current_Priority;

         Current_Task.Common.LL.Active_Priority :=
           Current_Task.Common.Current_Priority;
         Current_Task.Common.LL.Outer_Lock := null;

      else
         --  If this lock is nested, pop the old active priority.

         Current_Task.Common.LL.Active_Priority := L.Pre_Locking_Priority;
      end if;

      --  Reschedule the task if necessary. Note we only need to reschedule
      --  the task if its Active_Priority becomes less than the one following
      --  it. The check depends on the fact that Environment_Task (tail of
      --  the ready queue) has the lowest Active_Priority

      if Current_Task.Common.LL.Active_Priority
        < To_Task_ID (Current_Task.Common.LL.Succ).Common.LL.Active_Priority
      then
         R_Save_Flags (Flags);
         R_Cli;
         Delete_R (Current_Task);
         Insert_RF (Current_Task);
         R_Restore_Flags (Flags);
         Rt_Schedule;
      end if;
   end Unlock;

   procedure Unlock (L : access RTS_Lock) is
      Flags : Integer;
   begin
      pragma Debug (Printk ("procedure Unlock (RTS_Lock) called" & LF));

      if L.Owner /= To_Address (Current_Task) then
         null;
         Printk ("The caller is not the owner of the lock" & LF);
         return;
      end if;

      L.Owner := System.Null_Address;

      if Current_Task.Common.LL.Outer_Lock = L.all'Unchecked_Access then
         Current_Task.Common.LL.Active_Priority :=
           Current_Task.Common.Current_Priority;
         Current_Task.Common.LL.Outer_Lock := null;

      else
         Current_Task.Common.LL.Active_Priority := L.Pre_Locking_Priority;
      end if;

      --  Reschedule the task if necessary

      if Current_Task.Common.LL.Active_Priority
        < To_Task_ID (Current_Task.Common.LL.Succ).Common.LL.Active_Priority
      then
         R_Save_Flags (Flags);
         R_Cli;
         Delete_R (Current_Task);
         Insert_RF (Current_Task);
         R_Restore_Flags (Flags);
         Rt_Schedule;
      end if;
   end Unlock;

   procedure Unlock (T : Task_ID) is
   begin
      pragma Debug (Printk ("procedure Unlock (Task_ID) called" & LF));
      Unlock (T.Common.LL.L'Access);
   end Unlock;

   -----------
   -- Sleep --
   -----------

   --  Unlock Self_ID.Common.LL.L and suspend Self_ID, atomically.
   --  Before return, lock Self_ID.Common.LL.L again
   --  Self_ID can only be reactivated by calling Wakeup.
   --  Unlock code is repeated intentionally.

   procedure Sleep
     (Self_ID : Task_ID;
      Reason  : ST.Task_States)
   is
      Flags : Integer;
   begin
      pragma Debug (Printk ("procedure Sleep called" & LF));

      --  Note that Self_ID is actually Current_Task, that is, only the
      --  task that is running can put itself into sleep. To preserve
      --  consistency, we use Self_ID throughout the code here

      Self_ID.Common.State := Reason;
      Self_ID.Common.LL.State := RT_TASK_DORMANT;

      R_Save_Flags (Flags);
      R_Cli;

      Delete_R (Self_ID);

      --  Arrange to unlock Self_ID's ATCB lock. The following check
      --  may be unnecessary because the specification of Sleep says
      --  the caller shoud hold its own ATCB lock before calling Sleep

      if Self_ID.Common.LL.L.Owner = To_Address (Self_ID) then
         Self_ID.Common.LL.L.Owner := System.Null_Address;

         if Self_ID.Common.LL.Outer_Lock = Self_ID.Common.LL.L'Access then
            Self_ID.Common.LL.Active_Priority :=
              Self_ID.Common.Current_Priority;
            Self_ID.Common.LL.Outer_Lock := null;

         else
            Self_ID.Common.LL.Active_Priority :=
              Self_ID.Common.LL.L.Pre_Locking_Priority;
         end if;
      end if;

      R_Restore_Flags (Flags);
      Rt_Schedule;

      --  Before leave, regain the lock

      Write_Lock (Self_ID);
   end Sleep;

   -----------------
   -- Timed_Sleep --
   -----------------

   --  Arrange to be awakened after/at Time (depending on Mode) then Unlock
   --  Self_ID.Common.LL.L and suspend self. If the timeout expires first,
   --  that should awaken the task. If it's awakened (by some other task
   --  calling Wakeup) before the timeout expires, the timeout should be
   --  cancelled.

   --  This is for use within the run-time system, so abort is
   --  assumed to be already deferred, and the caller should be
   --  holding its own ATCB lock.

   procedure Timed_Sleep
     (Self_ID  : Task_ID;
      Time     : Duration;
      Mode     : ST.Delay_Modes;
      Reason   : Task_States;
      Timedout : out Boolean;
      Yielded  : out Boolean)
   is
      Flags      : Integer;
      Abs_Time   : RTIME;

   begin
      pragma Debug (Printk ("procedure Timed_Sleep called" & LF));

      Timedout := True;
      Yielded := False;
      --  ??? These two boolean seems not relevant here

      if Mode = Relative then
         Abs_Time := To_RTIME (Time) + Rt_Get_Time;
      else
         Abs_Time := To_RTIME (Time);
      end if;

      Self_ID.Common.LL.Resume_Time := Abs_Time;
      Self_ID.Common.LL.State := RT_TASK_DELAYED;

      R_Save_Flags (Flags);
      R_Cli;
      Delete_R (Self_ID);
      Insert_T (Self_ID);

      --  Check if the timer needs to be set

      if Timer_Queue.Common.LL.Succ = To_Address (Self_ID) then
         Rt_Set_Timer (Abs_Time);
      end if;

      --  Another way to do it
      --
      --  if Abs_Time <
      --    To_Task_ID (Timer_Queue.Common.LL.Succ).Common.LL.Resume_Time
      --  then
      --     Rt_Set_Timer (Abs_Time);
      --  end if;

      --  Arrange to unlock Self_ID's ATCB lock. see comments in Sleep

      if Self_ID.Common.LL.L.Owner = To_Address (Self_ID) then
         Self_ID.Common.LL.L.Owner := System.Null_Address;

         if Self_ID.Common.LL.Outer_Lock = Self_ID.Common.LL.L'Access then
            Self_ID.Common.LL.Active_Priority :=
              Self_ID.Common.Current_Priority;
            Self_ID.Common.LL.Outer_Lock := null;

         else
            Self_ID.Common.LL.Active_Priority :=
              Self_ID.Common.LL.L.Pre_Locking_Priority;
         end if;
      end if;

      R_Restore_Flags (Flags);
      Rt_Schedule;

      --  Before leaving, regain the lock

      Write_Lock (Self_ID);
   end Timed_Sleep;

   -----------------
   -- Timed_Delay --
   -----------------

   --  This is for use in implementing delay statements, so we assume
   --  the caller is not abort-deferred and is holding no locks.
   --  Self_ID can only be awakened after the timeout, no Wakeup on it.

   procedure Timed_Delay
     (Self_ID  : Task_ID;
      Time     : Duration;
      Mode     : ST.Delay_Modes)
   is
      Flags      : Integer;
      Abs_Time   : RTIME;

   begin
      pragma Debug (Printk ("procedure Timed_Delay called" & LF));

      --  Only the little window between deferring abort and
      --  locking Self_ID is the reason we need to
      --  check for pending abort and priority change below! :(

      Write_Lock (Self_ID);

      --  Take the lock in case its ATCB needs to be modified

      if Mode = Relative then
         Abs_Time := To_RTIME (Time) + Rt_Get_Time;
      else
         Abs_Time := To_RTIME (Time);
      end if;

      Self_ID.Common.LL.Resume_Time := Abs_Time;
      Self_ID.Common.LL.State := RT_TASK_DELAYED;

      R_Save_Flags (Flags);
      R_Cli;
      Delete_R (Self_ID);
      Insert_T (Self_ID);

      --  Check if the timer needs to be set

      if Timer_Queue.Common.LL.Succ = To_Address (Self_ID) then
         Rt_Set_Timer (Abs_Time);
      end if;

      --  Arrange to unlock Self_ID's ATCB lock.
      --  Note that the code below is slightly different from Unlock, so
      --  it is more than inline it.

      if To_Task_ID (Self_ID.Common.LL.L.Owner) = Self_ID then
         Self_ID.Common.LL.L.Owner := System.Null_Address;

         if Self_ID.Common.LL.Outer_Lock = Self_ID.Common.LL.L'Access then
            Self_ID.Common.LL.Active_Priority :=
              Self_ID.Common.Current_Priority;
            Self_ID.Common.LL.Outer_Lock := null;

         else
            Self_ID.Common.LL.Active_Priority :=
              Self_ID.Common.LL.L.Pre_Locking_Priority;
         end if;
      end if;

      R_Restore_Flags (Flags);
      Rt_Schedule;
   end Timed_Delay;

   ---------------------
   -- Monotonic_Clock --
   ---------------------

   --  RTIME is represented as a 64-bit signed count of ticks,
   --  where there are 1_193_180 ticks per second.

   --  Let T be a count of ticks and N the corresponding count of nanoseconds.
   --  From the following relationship
   --    T / (ticks_per_second) = N / (ns_per_second)
   --  where ns_per_second is 1_000_000_000 (number of nanoseconds in
   --  a second), we get
   --    T * (ns_per_second) = N * (ticks_per_second)
   --  or
   --    T * 1_000_000_000   = N * 1_193_180
   --  which can be reduced to
   --    T * 50_000_000      = N * 59_659
   --  Let Nano_Count = 50_000_000 and Tick_Count = 59_659, we then have
   --    T * Nano_Count = N * Tick_Count

   --  IMPORTANT FACT:
   --  These numbers are small enough that we can do arithmetic
   --  on them without overflowing 64 bits.  To see this, observe

   --  10**3 = 1000 < 1024 = 2**10
   --  Tick_Count < 60 * 1000 < 64 * 1024 < 2**16
   --  Nano_Count < 50 * 1000 * 1000 < 64 * 1024 * 1024 < 2**26

   --  It follows that if 0 <= R < Tick_Count, we can compute
   --  R * Nano_Count < 2**42 without overflow in 64 bits.
   --  Similarly, if 0 <= R < Nano_Count, we can compute
   --  R * Tick_Count < 2**42 without overflow in 64 bits.

   --  GNAT represents Duration as a count of nanoseconds internally.

   --  To convert T from RTIME to Duration, let
   --    Q = T / Tick_Count, with truncation
   --    R = T - Q * Tick_Count, the remainder 0 <= R < Tick_Count
   --  so
   --    N * Tick_Count
   --      =  T * Nano_Count - Q * Tick_Count * Nano_Count
   --         + Q * Tick_Count * Nano_Count
   --      = (T - Q * Tick_Count) * Nano_Count
   --         + (Q * Nano_Count) * Tick_Count
   --      =  R * Nano_Count + (Q * Nano_Count) * Tick_Count

   --  Now, let
   --    Q1 = R * Nano_Count / Tick_Count, with truncation
   --    R1 = R * Nano_Count - Q1 * Tick_Count, 0 <= R1 <Tick_Count
   --    R * Nano_Count = Q1 * Tick_Count + R1
   --  so
   --    N * Tick_Count
   --      = R * Nano_Count + (Q * Nano_Count) * Tick_Count
   --      = Q1 * Tick_Count + R1 + (Q * Nano_Count) * Tick_Count
   --      = R1 + (Q * Nano_Count + Q1) * Tick_Count
   --  and
   --    N = Q * Nano_Count + Q1 + R1 /Tick_Count,
   --    where 0 <= R1 /Tick_Count < 1

   function To_Duration (T : RTIME) return Duration is
      Q, Q1, RN : RTIME;
   begin
      Q  := T / Tick_Count;
      RN := (T - Q * Tick_Count) * Nano_Count;
      Q1 := RN / Tick_Count;
      return Raw_Duration (Q * Nano_Count + Q1);
   end To_Duration;

   --  To convert D from Duration to RTIME,
   --  Let D be a Duration value, and N be the representation of D as an
   --  integer count of nanoseconds. Let
   --    Q = N / Nano_Count, with truncation
   --    R = N - Q * Nano_Count, the remainder 0 <= R < Nano_Count
   --  so
   --    T * Nano_Count
   --      = N * Tick_Count - Q * Nano_Count * Tick_Count
   --        + Q * Nano_Count * Tick_Count
   --      = (N - Q * Nano_Count) * Tick_Count
   --         + (Q * Tick_Count) * Nano_Count
   --      = R * Tick_Count + (Q * Tick_Count) * Nano_Count
   --  Now, let
   --    Q1 = R * Tick_Count / Nano_Count, with truncation
   --    R1 = R * Tick_Count - Q1 * Nano_Count, 0 <= R1 < Nano_Count
   --    R * Tick_Count = Q1 * Nano_Count + R1
   --  so
   --    T * Nano_Count
   --      = R * Tick_Count + (Q * Tick_Count) * Nano_Count
   --      = Q1 * Nano_Count + R1 + (Q * Tick_Count) * Nano_Count
   --      = (Q * Tick_Count + Q1) * Nano_Count + R1
   --  and
   --    T = Q * Tick_Count + Q1 + R1 / Nano_Count,
   --    where 0 <= R1 / Nano_Count < 1

   function To_RTIME (D : Duration) return RTIME is
      N : RTIME := Raw_RTIME (D);
      Q, Q1, RT : RTIME;

   begin
      Q  := N / Nano_Count;
      RT := (N - Q * Nano_Count) * Tick_Count;
      Q1 := RT / Nano_Count;
      return Q * Tick_Count + Q1;
   end To_RTIME;

   function Monotonic_Clock return Duration is
   begin
      pragma Debug (Printk ("procedure Clock called" & LF));

      return To_Duration (Rt_Get_Time);
   end Monotonic_Clock;

   -------------------
   -- RT_Resolution --
   -------------------

   function RT_Resolution return Duration is
   begin
      return 10#1.0#E-6;
   end RT_Resolution;

   ------------
   -- Wakeup --
   ------------

   procedure Wakeup (T : Task_ID; Reason : ST.Task_States) is
      Flags : Integer;
   begin
      pragma Debug (Printk ("procedure Wakeup called" & LF));

      T.Common.State := Reason;
      T.Common.LL.State := RT_TASK_READY;

      R_Save_Flags (Flags);
      R_Cli;

      if Timer_Queue.Common.LL.Succ = To_Address (T) then
         --  T is the first task in Timer_Queue, further check

         if T.Common.LL.Succ = Timer_Queue'Address then
            --  T is the only task in Timer_Queue, so deactivate timer

            Rt_No_Timer;

         else
            --  T is the first task in Timer_Queue, so set timer to T's
            --  successor's Resume_Time

            Rt_Set_Timer (To_Task_ID (T.Common.LL.Succ).Common.LL.Resume_Time);
         end if;
      end if;

      Delete_T (T);

      --  If T is in Timer_Queue, T is removed. If not, nothing happened

      Insert_R (T);
      R_Restore_Flags (Flags);

      Rt_Schedule;
   end Wakeup;

   -----------
   -- Yield --
   -----------

   procedure Yield (Do_Yield : Boolean := True) is
      Flags : Integer;
   begin
      pragma Debug (Printk ("procedure Yield called" & LF));

      pragma Assert (Current_Task /= To_Task_ID (Idle_Task'Address));

      R_Save_Flags (Flags);
      R_Cli;
      Delete_R (Current_Task);
      Insert_R (Current_Task);

      --  Remove Current_Task from the top of the Ready_Queue
      --  and reinsert it back at proper position (the end of
      --  tasks with the same active priority).

      R_Restore_Flags (Flags);
      Rt_Schedule;
   end Yield;

   ------------------
   -- Set_Priority --
   ------------------

   --  This version implicitly assume that T is the Current_Task

   procedure Set_Priority
     (T                   : Task_ID;
      Prio                : System.Any_Priority;
      Loss_Of_Inheritance : Boolean := False)
   is
      Flags : Integer;
   begin
      pragma Debug (Printk ("procedure Set_Priority called" & LF));
      pragma Assert (T = Self);

      T.Common.Current_Priority := Prio;

      if T.Common.LL.Outer_Lock /= null then
         --  If the task T is holding any lock, defer the priority change
         --  until the lock is released. That is, T's Active_Priority will
         --  be set to Prio after it unlocks the outer-most lock. See
         --  Unlock for detail.
         --  Nothing needs to be done here for this case

         null;
      else
         --  If T is not holding any lock, change the priority right away.

         R_Save_Flags (Flags);
         R_Cli;
         T.Common.LL.Active_Priority := Prio;
         Delete_R (T);
         Insert_RF (T);

         --  Insert at the front of the queue for its new priority

         R_Restore_Flags (Flags);
      end if;

      Rt_Schedule;
   end Set_Priority;

   ------------------
   -- Get_Priority --
   ------------------

   function Get_Priority (T : Task_ID) return System.Any_Priority is
   begin
      pragma Debug (Printk ("procedure Get_Priority called" & LF));

      return T.Common.Current_Priority;
   end Get_Priority;

   ----------------
   -- Enter_Task --
   ----------------

   --  Do any target-specific initialization that is needed for a new task
   --  that has to be done by the task itself. This is called from the task
   --  wrapper, immediately after the task starts execution.

   procedure Enter_Task (Self_ID : Task_ID) is
   begin
      --  Use this as "hook" to re-enable interrupts.
      pragma Debug (Printk ("procedure Enter_Task called" & LF));

      R_Sti;
   end Enter_Task;

   ----------------
   --  New_ATCB  --
   ----------------

   function New_ATCB (Entry_Num : Task_Entry_Index) return Task_ID is
      T : constant Task_ID := Available_TCBs;
   begin
      pragma Debug (Printk ("function New_ATCB called" & LF));

      if Entry_Num /= 0 then
         --  We are preallocating all TCBs, so they must all have the
         --  same number of entries, which means the value of
         --  Entry_Num must be bounded.  We probably could choose a
         --  non-zero upper bound here, but the Ravenscar Profile
         --  specifies that there be no task entries.
         --  ???
         --  Later, do something better for recovery from this error.

         null;
      end if;

      if T /= null then
         Available_TCBs := To_Task_ID (T.Common.LL.Next);
         T.Common.LL.Next := System.Null_Address;
         Known_Tasks (T.Known_Tasks_Index) := T;
      end if;

      return T;
   end New_ATCB;

   ----------------------
   --  Initialize_TCB  --
   ----------------------

   procedure Initialize_TCB (Self_ID : Task_ID; Succeeded : out Boolean) is
   begin
      pragma Debug (Printk ("procedure Initialize_TCB called" & LF));

      --  Give the task a unique serial number.

      Self_ID.Serial_Number := Next_Serial_Number;
      Next_Serial_Number := Next_Serial_Number + 1;
      pragma Assert (Next_Serial_Number /= 0);

      Self_ID.Common.LL.L.Ceiling_Priority := System.Any_Priority'Last;
      Self_ID.Common.LL.L.Owner := System.Null_Address;
      Succeeded := True;
   end Initialize_TCB;

   -----------------
   -- Create_Task --
   -----------------

   procedure Create_Task
     (T          : Task_ID;
      Wrapper    : System.Address;
      Stack_Size : System.Parameters.Size_Type;
      Priority   : System.Any_Priority;
      Succeeded  : out Boolean)
   is
      Adjusted_Stack_Size : Integer;
      Bottom              : System.Address;
      Flags               : Integer;

   begin
      pragma Debug (Printk ("procedure Create_Task called" & LF));

      Succeeded := True;

      if T.Common.LL.Magic = RT_TASK_MAGIC then
         Succeeded := False;
         return;
      end if;

      if Stack_Size = Unspecified_Size then
         Adjusted_Stack_Size := To_Integer (Default_Stack_Size);
      elsif Stack_Size < Minimum_Stack_Size then
         Adjusted_Stack_Size := To_Integer (Minimum_Stack_Size);
      else
         Adjusted_Stack_Size := To_Integer (Stack_Size);
      end if;

      Bottom := Kmalloc (Adjusted_Stack_Size, GFP_KERNEL);

      if Bottom = System.Null_Address then
         Succeeded := False;
         return;
      end if;

      T.Common.LL.Uses_Fp          := 1;

      --  This field has to be reset to 1 if T uses FP unit. But, without
      --  a library-level procedure provided by this package, it cannot
      --  be set easily. So temporarily, set it to 1 (which means all the
      --  tasks will use FP unit. ???

      T.Common.LL.Magic            := RT_TASK_MAGIC;
      T.Common.LL.State            := RT_TASK_READY;
      T.Common.LL.Succ             := To_Address (T);
      T.Common.LL.Pred             := To_Address (T);
      T.Common.LL.Active_Priority  := Priority;
      T.Common.Current_Priority    := Priority;

      T.Common.LL.Stack_Bottom := Bottom;
      T.Common.LL.Stack := Bottom + Storage_Offset (Adjusted_Stack_Size);

      --  Store the value T into the stack, so that Task_wrapper (defined
      --  in System.Tasking.Stages) will find that value for its parameter
      --  Self_ID, when the scheduler eventually transfers control to the
      --  new task.

      T.Common.LL.Stack := T.Common.LL.Stack - Addr_Bytes;
      To_Address_Ptr (T.Common.LL.Stack).all := To_Address (T);

      --  Leave space for the return address, which will not be used,
      --  since the task wrapper should never return.

      T.Common.LL.Stack := T.Common.LL.Stack - Addr_Bytes;
      To_Address_Ptr (T.Common.LL.Stack).all := System.Null_Address;

      --  Put the entry point address of the task wrapper
      --  procedure on the new top of the stack.

      T.Common.LL.Stack := T.Common.LL.Stack - Addr_Bytes;
      To_Address_Ptr (T.Common.LL.Stack).all := Wrapper;

      R_Save_Flags (Flags);
      R_Cli;
      Insert_R (T);
      R_Restore_Flags (Flags);
   end Create_Task;

   ------------------
   -- Finalize_TCB --
   ------------------

   procedure Finalize_TCB (T : Task_ID) is
   begin
      pragma Debug (Printk ("procedure Finalize_TCB called" & LF));

      pragma Assert (T.Common.LL.Succ = To_Address (T));

      if T.Common.LL.State = RT_TASK_DORMANT then
         Known_Tasks (T.Known_Tasks_Index) := null;
         T.Common.LL.Next := To_Address (Available_TCBs);
         Available_TCBs := T;
         Kfree (T.Common.LL.Stack_Bottom);
      end if;
   end Finalize_TCB;

   ---------------
   -- Exit_Task --
   ---------------

   procedure Exit_Task is
      Flags : Integer;
   begin
      pragma Debug (Printk ("procedure Exit_Task called" & LF));
      pragma Assert (Current_Task /= To_Task_ID (Idle_Task'Address));
      pragma Assert (Current_Task /= Environment_Task_ID);

      R_Save_Flags (Flags);
      R_Cli;
      Current_Task.Common.LL.State := RT_TASK_DORMANT;
      Current_Task.Common.LL.Magic := 0;
      Delete_R (Current_Task);
      R_Restore_Flags (Flags);
      Rt_Schedule;
   end Exit_Task;

   ----------------
   -- Abort_Task --
   ----------------

   --  ??? Not implemented for now

   procedure Abort_Task (T : Task_ID) is
   --  Should cause T to raise Abort_Signal the next time it
   --  executes.
   --  ??? Can this ever be called when T = Current_Task?
   --  To be safe, do nothing in this case.
   begin
      pragma Debug (Printk ("procedure Abort_Task called" & LF));
      null;
   end Abort_Task;

   ----------------
   -- Check_Exit --
   ----------------

   --  Dummy versions. The only currently working versions is for solaris
   --  (native).
   --  We should probably copy the working versions over from the Solaris
   --  version of this package, with any appropriate changes, since without
   --  the checks on it will probably be nearly impossible to debug the
   --  run-time system.

   --  Not implemented for now

   function Check_Exit (Self_ID : Task_ID) return Boolean is
   begin
      pragma Debug (Printk ("function Check_Exit called" & LF));

      return True;
   end Check_Exit;

   --------------------
   -- Check_No_Locks --
   --------------------

   function Check_No_Locks (Self_ID : Task_ID) return Boolean is
   begin
      pragma Debug (Printk ("function Check_No_Locks called" & LF));

      if Self_ID.Common.LL.Outer_Lock = null then
         return True;
      else
         return False;
      end if;
   end Check_No_Locks;

   ----------------------
   -- Environment_Task --
   ----------------------

   function Environment_Task return Task_ID is
   begin
      return Environment_Task_ID;
   end Environment_Task;

   -------------------------
   -- Lock_All_Tasks_List --
   -------------------------

   procedure Lock_All_Tasks_List is
   begin
      pragma Debug (Printk ("procedure Lock_All_Tasks_List called" & LF));

      Write_Lock (All_Tasks_L'Access);
   end Lock_All_Tasks_List;

   ---------------------------
   -- Unlock_All_Tasks_List --
   ---------------------------

   procedure Unlock_All_Tasks_List is
   begin
      pragma Debug (Printk ("procedure Unlock_All_Tasks_List called" & LF));

      Unlock (All_Tasks_L'Access);
   end Unlock_All_Tasks_List;

   -----------------
   -- Stack_Guard --
   -----------------

   --  Not implemented for now

   procedure Stack_Guard (T : Task_ID; On : Boolean) is
   begin
      null;
   end Stack_Guard;

   --------------------
   -- Get_Thread_Id  --
   --------------------

   function Get_Thread_Id (T : Task_ID) return OSI.Thread_Id is
   begin
      return To_Address (T);
   end Get_Thread_Id;

   ------------------
   -- Suspend_Task --
   ------------------

   function Suspend_Task
     (T           : Task_ID;
      Thread_Self : OSI.Thread_Id) return Boolean is
   begin
      return False;
   end Suspend_Task;

   -----------------
   -- Resume_Task --
   -----------------

   function Resume_Task
     (T           : ST.Task_ID;
      Thread_Self : OSI.Thread_Id) return Boolean is
   begin
      return False;
   end Resume_Task;

   -----------------
   -- Init_Module --
   -----------------

   function Init_Module return Integer is
      procedure adainit;
      pragma Import (C, adainit);

   begin
      adainit;
      In_Elab_Code := False;
      Set_Priority (Environment_Task_ID, Any_Priority'First);
      return 0;
   end Init_Module;

   --------------------
   -- Cleanup_Module --
   --------------------

   procedure Cleanup_Module is
      procedure adafinal;
      pragma Import (C, adafinal);

   begin
      adafinal;
   end Cleanup_Module;

   ----------------
   -- Initialize --
   ----------------

   --  The environment task is "special". The TCB of the environment task is
   --  not in the TCB_Array above. Logically, all initialization code for the
   --  runtime system is executed by the environment task, but until the
   --  environment task has initialized its own TCB we dare not execute any
   --  calls that try to access the TCB of Current_Task. It is allocated by
   --  target-independent runtime system code, in System.Tasking.Initializa-
   --  tion.Init_RTS, before the call to this procedure Initialize. The
   --  target-independent runtime system initializes all the components that
   --  are target-independent, but this package needs to be given a chance to
   --  initialize the target-dependent data.  We do that in this procedure.

   --  In the present implementation, Environment_Task is set to be the
   --  regular GNU/Linux kernel task.

   procedure Initialize (Environment_Task : Task_ID) is
   begin
      pragma Debug (Printk ("procedure Initialize called" & LF));

      Environment_Task_ID := Environment_Task;

      --  Build the list of available ATCB's.

      Available_TCBs := To_Task_ID (TCB_Array (1)'Address);

      for J in TCB_Array'First + 1 .. TCB_Array'Last - 1 loop
         --  Note that the zeroth element in TCB_Array is not used, see
         --  comments following the declaration of TCB_Array

         TCB_Array (J).Common.LL.Next := TCB_Array (J + 1)'Address;
      end loop;

      TCB_Array (TCB_Array'Last).Common.LL.Next := System.Null_Address;

      --  Initialize the idle task, which is the head of Ready_Queue.

      Idle_Task.Common.LL.Magic := RT_TASK_MAGIC;
      Idle_Task.Common.LL.State := RT_TASK_READY;
      Idle_Task.Common.Current_Priority := System.Any_Priority'First;
      Idle_Task.Common.LL.Active_Priority  := System.Any_Priority'First;
      Idle_Task.Common.LL.Succ := Idle_Task'Address;
      Idle_Task.Common.LL.Pred := Idle_Task'Address;

      --  Initialize the regular GNU/Linux kernel task.

      Environment_Task.Common.LL.Magic := RT_TASK_MAGIC;
      Environment_Task.Common.LL.State := RT_TASK_READY;
      Environment_Task.Common.Current_Priority := System.Any_Priority'First;
      Environment_Task.Common.LL.Active_Priority  := System.Any_Priority'First;
      Environment_Task.Common.LL.Succ := To_Address (Environment_Task);
      Environment_Task.Common.LL.Pred := To_Address (Environment_Task);

      --  Initialize the head of Timer_Queue

      Timer_Queue.Common.LL.Succ        := Timer_Queue'Address;
      Timer_Queue.Common.LL.Pred        := Timer_Queue'Address;
      Timer_Queue.Common.LL.Resume_Time := Max_Sensible_Delay;

      --  Set the current task to regular GNU/Linux kernel task

      Current_Task := Environment_Task;

      --  Set Timer_Wrapper to be the timer handler

      Rt_Free_Timer;
      Rt_Request_Timer (Timer_Wrapper'Address);

      --  Initialize the lock used to synchronize chain of all ATCBs.

      Initialize_Lock (All_Tasks_L'Access, All_Tasks_Level);

      Enter_Task (Environment_Task);
   end Initialize;

end System.Task_Primitives.Operations;