On Fri, Jun 26, 2020 at 09:06:58PM +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 [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
Thanks. I committed this change. -Kevin _______________________________________________ SeaBIOS mailing list -- seabios@seabios.org To unsubscribe send an email to seabios-le...@seabios.org
