Implement single memory read access.

Prevent unaligned accesses in memory read.

Also change how exceptions in Debug Mode are signaled.

2 files changed, 29 insertions, 24 deletions

diff --git a/debug_rom/debug_rom.S b/debug_rom/debug_rom.S
index b1fa8bd..35dd406 100755
--- a/debug_rom/debug_rom.S
+++ b/debug_rom/debug_rom.S
@@ -29,15 +29,14 @@ entry:  j       _entry
 resume:
         j       _resume
 exception:
-        # Flip the LSB of the first word in Debug RAM so the debugger can know
-        # that we hit an exception.
-        lw      s1, (DEBUG_RAM)(zero)
-        xori    s1, s1, 1
-        sw      s1, (DEBUG_RAM)(zero)
-
-        # Fall through to resume.
+        # Set the last word of Debug RAM to all ones, to indicate that we hit
+        # an exception.
+        li      s0, ~0
+        j       _resume2
 
 _resume:
+        li      s0, 0
+_resume2:
         # Clear debug interrupt.
         csrr    s1, CSR_MHARTID
         sw      s1, CLEARDEBINT(zero)
@@ -58,6 +57,11 @@ restore_64:
 restore_128:
         nop     #lq      s1, (DEBUG_RAM + DEBUG_RAM_SIZE - 16)(zero)
 
+        # s0 contains ~0 if we got here through an exception, and 0 otherwise.
+        # Store this to the last word in Debug RAM so the debugger can tell if
+        # an exception occurred.
+        sw      s0, (DEBUG_RAM + DEBUG_RAM_SIZE - 4)(zero)
+
 check_halt:
         csrr    s0, DCSR
         andi    s0, s0, (1<<DCSR_HALT_OFFSET)
@@ -68,7 +72,7 @@ exit:
         # Restore s0.
         csrr    s0, DSCRATCH
         # TODO: dret?
-        mret
+        sret
 
 
 _entry:
diff --git a/debug_rom/debug_rom.h b/debug_rom/debug_rom.h
index f8aa2e0..8b5ea69 100644
--- a/debug_rom/debug_rom.h
+++ b/debug_rom/debug_rom.h
@@ -1,18 +1,19 @@
 static const unsigned char debug_rom_raw[] = {
-  0x6f, 0x00, 0xc0, 0x05, 0x6f, 0x00, 0x00, 0x01, 0x83, 0x24, 0x00, 0xc0,
-  0x93, 0xc4, 0x14, 0x00, 0x23, 0x20, 0x90, 0xc0, 0xf3, 0x24, 0x50, 0xf1,
-  0x23, 0x2c, 0x90, 0xee, 0x0f, 0x00, 0xf0, 0x0f, 0xf3, 0x24, 0x00, 0xf1,
-  0x63, 0xc6, 0x04, 0x00, 0x83, 0x24, 0xc0, 0xc3, 0x6f, 0x00, 0x80, 0x01,
-  0x93, 0x94, 0x14, 0x00, 0x63, 0xc6, 0x04, 0x00, 0x83, 0x34, 0x80, 0xc3,
-  0x6f, 0x00, 0x80, 0x00, 0x13, 0x00, 0x00, 0x00, 0x73, 0x24, 0x00, 0x79,
-  0x13, 0x74, 0x84, 0x00, 0x63, 0x04, 0x04, 0x00, 0x6f, 0x00, 0x40, 0x05,
-  0x73, 0x24, 0x20, 0x79, 0x73, 0x00, 0x20, 0x10, 0x73, 0x10, 0x24, 0x79,
-  0x73, 0x24, 0x00, 0x79, 0x13, 0x74, 0x74, 0x00, 0x13, 0x04, 0xd4, 0xff,
-  0x63, 0x16, 0x04, 0x02, 0x73, 0x24, 0x00, 0xf1, 0x63, 0x46, 0x04, 0x00,
-  0x23, 0x2e, 0x90, 0xc2, 0x67, 0x00, 0x00, 0xc0, 0x13, 0x14, 0x14, 0x00,
-  0x63, 0x46, 0x04, 0x00, 0x23, 0x3c, 0x90, 0xc2, 0x67, 0x00, 0x00, 0xc0,
-  0x13, 0x00, 0x00, 0x00, 0x67, 0x00, 0x00, 0xc0, 0x73, 0x24, 0x50, 0xf1,
-  0x23, 0x20, 0x80, 0xf0, 0x73, 0x60, 0x04, 0x79, 0x73, 0x24, 0x00, 0x79,
-  0x13, 0x74, 0x04, 0x40, 0xe3, 0x0c, 0x04, 0xfe, 0x6f, 0xf0, 0x1f, 0xfc
+  0x6f, 0x00, 0x00, 0x06, 0x6f, 0x00, 0xc0, 0x00, 0x13, 0x04, 0xf0, 0xff,
+  0x6f, 0x00, 0x80, 0x00, 0x13, 0x04, 0x00, 0x00, 0xf3, 0x24, 0x40, 0xf1,
+  0x23, 0x24, 0x90, 0x10, 0x0f, 0x00, 0xf0, 0x0f, 0xf3, 0x24, 0x00, 0xf1,
+  0x63, 0xc6, 0x04, 0x00, 0x83, 0x24, 0xc0, 0x43, 0x6f, 0x00, 0xc0, 0x01,
+  0x93, 0x94, 0x14, 0x00, 0x63, 0xc6, 0x04, 0x00, 0x83, 0x34, 0x80, 0x43,
+  0x6f, 0x00, 0xc0, 0x00, 0x13, 0x00, 0x00, 0x00, 0x23, 0x2e, 0x80, 0x42,
+  0x73, 0x24, 0x00, 0x79, 0x13, 0x74, 0x84, 0x00, 0x63, 0x04, 0x04, 0x00,
+  0x6f, 0x00, 0x40, 0x05, 0x73, 0x24, 0x20, 0x79, 0x73, 0x00, 0x00, 0x10,
+  0x73, 0x10, 0x24, 0x79, 0x73, 0x24, 0x00, 0x79, 0x13, 0x74, 0x74, 0x00,
+  0x13, 0x04, 0xd4, 0xff, 0x63, 0x16, 0x04, 0x02, 0x73, 0x24, 0x00, 0xf1,
+  0x63, 0x46, 0x04, 0x00, 0x23, 0x2e, 0x90, 0x42, 0x67, 0x00, 0x00, 0x40,
+  0x13, 0x14, 0x14, 0x00, 0x63, 0x46, 0x04, 0x00, 0x23, 0x3c, 0x90, 0x42,
+  0x67, 0x00, 0x00, 0x40, 0x13, 0x00, 0x00, 0x00, 0x67, 0x00, 0x00, 0x40,
+  0x73, 0x24, 0x40, 0xf1, 0x23, 0x20, 0x80, 0x10, 0x73, 0x60, 0x04, 0x79,
+  0x73, 0x24, 0x00, 0x79, 0x13, 0x74, 0x04, 0x40, 0xe3, 0x0c, 0x04, 0xfe,
+  0x6f, 0xf0, 0x1f, 0xfc
 };
-static const unsigned int debug_rom_raw_len = 180;
+static const unsigned int debug_rom_raw_len = 184;