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| author | Roman Bolshakov <r.bolshakov@yadro.com> | 2020-06-26 21:06:58 +0300 |
|---|---|---|
| committer | Kevin O'Connor <kevin@koconnor.net> | 2020-06-26 14:18:23 -0400 |
| commit | 88ab0c15525ced2eefe39220742efe4769089ad8 (patch) | |
| tree | eac2b70a3b1575c0739be723449bce1f1403b360 /src/hw/timer.c | |
| parent | d11c75185276ded944f2ea0277532b7fee849bbc (diff) | |
| download | seabios-hppa-88ab0c15525ced2eefe39220742efe4769089ad8.zip seabios-hppa-88ab0c15525ced2eefe39220742efe4769089ad8.tar.gz seabios-hppa-88ab0c15525ced2eefe39220742efe4769089ad8.tar.bz2 | |
timer: Handle decrements of PIT counter
There's a fallback to PIT if TSC is not present but it doesn't work
properly. It prevents boot from floppy on isapc and 486 cpu [1][2].
SeaBIOS configures PIT in Mode 2. PIT counter is decremented in the mode
but timer_adjust_bits() thinks that the counter overflows and increases
32-bit tick counter on each detected "overflow". Invalid overflow
detection results in 55ms time advance (1 / 18.2Hz) on each read from
PIT counter. So all timers expire much faster and 5-second floppy
timeout expires in 83 real microseconds (or just a bit longer).
It can be fixed by making the counter recieved from PIT an increasing
value so it can be passed to timer_adjust_bits():
0, 1, 2 and up to 65535 and then the counter is re-loaded with 0.
1. https://bugs.launchpad.net/seabios/+bug/1840719
2. https://lists.gnu.org/archive/html/qemu-devel/2019-08/msg03924.html
Fixes: eac11944019 ("Unify pmtimer_read() and pittimer_read() code.")
Reported-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Roman Bolshakov <r.bolshakov@yadro.com>
Diffstat (limited to 'src/hw/timer.c')
| -rw-r--r-- | src/hw/timer.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/src/hw/timer.c b/src/hw/timer.c index 56bb289..b6f102e 100644 --- a/src/hw/timer.c +++ b/src/hw/timer.c @@ -180,7 +180,7 @@ timer_read(void) // Read from PIT. outb(PM_SEL_READBACK | PM_READ_VALUE | PM_READ_COUNTER0, PORT_PIT_MODE); u16 v = inb(PORT_PIT_COUNTER0) | (inb(PORT_PIT_COUNTER0) << 8); - return timer_adjust_bits(v, 0xffff); + return timer_adjust_bits(-v, 0xffff); } // Return the TSC value that is 'msecs' time in the future. |