On 8/20/19 3:12 PM, John Snow wrote:
On 8/20/19 6:25 AM, Philippe Mathieu-Daudé wrote:
[cross posting QEMU & SeaBIOS]
Hello,
I'v been looking at a QEMU bug report [1] which bisection resulted in a SeaBIOS commit:
4a6dbcea3e412fe12effa2f812f50dd7eae90955 is the first bad commit commit 4a6dbcea3e412fe12effa2f812f50dd7eae90955 Author: Nikolay Nikolov <nickysn@users.sourceforge.net> Date: Sun Feb 4 17:27:01 2018 +0200
floppy: Use timer_check() in floppy_wait_irq()
Use timer_check() instead of using floppy_motor_counter in BDA for the timeout check in floppy_wait_irq().
The problem with using floppy_motor_counter was that, after it reaches 0, it immediately stops the floppy motors, which is not what is supposed to happen on real hardware. Instead, after a timeout (like in the end of every floppy operation, regardless of the result - success, timeout or error), the floppy motors must be kept spinning for additional 2 seconds (the FLOPPY_MOTOR_TICKS). So, now the floppy_motor_counter is initialized to 255 (the max value) in the beginning of the floppy operation. For IRQ timeouts, a different timeout is used, specified by the new FLOPPY_IRQ_TIMEOUT constant (currently set to 5 seconds - a fairly conservative value, but should work reliably on most floppies).
After the floppy operation, floppy_drive_pio() resets the floppy_motor_counter to 2 seconds (FLOPPY_MOTOR_TICKS).
This is also consistent with what other PC BIOSes do.
This commit improve behavior with real hardware, so maybe QEMU is not modelling something or modelling it incorrectly? [...]
Well, that's unfortunate.
What version of QEMU shipped the SeaBIOS that caused the regression?
See https://bugs.launchpad.net/qemu/+bug/1840719/comments/3 QEMU commit 0b8f74488e, slighly before QEMU v3.1.0 (previous tag is v3.0.0). But you can use v4.1.0 too, simply change the SeaBIOS bios.bin, i.e.: qemu$ git checkout v4.1.0 qemu$ (cd roms/seabios && git checkout 4a6dbcea3e4~) && \ make -C roms bios Now pc-bios/bios.bin is built using the last commit working, qemu$ (cd roms/seabios && git checkout 4a6dbcea3e4) && \ make -C roms bios And you can reproduce the error. Regards, Phil.