On Sat, Jun 13, 2020 at 02:19:12PM +0300, Roman Bolshakov wrote: > 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 . > > 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). > > Provide counter direction to timer_adjust_bits() and normalize the > counter to advance ticks in monotonically increasing TimerLast.
Good catch. Could we fix it using the patch below instead though? -Kevin --- 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. _______________________________________________ SeaBIOS mailing list -- firstname.lastname@example.org To unsubscribe send an email to seabios-le...@seabios.org