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Re: [Qemu-devel] [SeaBIOS] Re: Regression with floppy drive controller
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [SeaBIOS] Re: Regression with floppy drive controller |
Date: |
Tue, 20 Aug 2019 15:36:14 +0100 |
User-agent: |
Mutt/1.12.1 (2019-06-15) |
* Philippe Mathieu-Daudé (address@hidden) wrote:
> On 8/20/19 3:38 PM, Philippe Mathieu-Daudé wrote:
> > 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 <address@hidden>
> >>> 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.
>
> Looking at the fdc timer I noticed it use a static '50 ns' magic value.
That's not 50ns
> Increasing this value allows the floppy image to boot again, using this
> snippet:
>
> -- >8 --
> diff --git a/hw/block/fdc.c b/hw/block/fdc.c
> index 9b24cb9b85..5fc54073fd 100644
> --- a/hw/block/fdc.c
> +++ b/hw/block/fdc.c
> @@ -2134,7 +2134,7 @@ static void fdctrl_handle_readid(FDCtrl *fdctrl,
> int direction)
>
> cur_drv->head = (fdctrl->fifo[1] >> 2) & 1;
> timer_mod(fdctrl->result_timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
> - (NANOSECONDS_PER_SECOND / 50));
That's 1/50th of a second in ns.
> + (NANOSECONDS_PER_SECOND / 5000));
I'm not too sure about readid; but assuming we're rotating at 360rpm,
that's 6 revolutions/second, and 18 sectors/track = 108 sectors/second
(half of that for a double density disk).
So, the wait for a sector to spin around and read feels like it should
be in the region of 1/108 of a second + some latency - so 1/50th of a
second would seem to be in the ballpark or being right, where as 1/5000
of a second is way too fast for a poor old floppy.
Dave
> }
>
> static void fdctrl_handle_format_track(FDCtrl *fdctrl, int direction)
> ---
>
> Any idea what is the correct value to use here?
>
> Regards,
>
> Phil.
> _______________________________________________
> SeaBIOS mailing list -- address@hidden
> To unsubscribe send an email to address@hidden
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
- [Qemu-devel] Regression with floppy drive controller, Philippe Mathieu-Daudé, 2019/08/20
- Re: [Qemu-devel] Regression with floppy drive controller, Philippe Mathieu-Daudé, 2019/08/20
- Re: [Qemu-devel] Regression with floppy drive controller, Eduardo Habkost, 2019/08/20
- Re: [Qemu-devel] Regression with floppy drive controller, Gerd Hoffmann, 2019/08/21
- Re: [Qemu-devel] Regression with floppy drive controller, Paolo Bonzini, 2019/08/21
- Re: [Qemu-devel] [SeaBIOS] Re: Regression with floppy drive controller, Kevin O'Connor, 2019/08/21
- Re: [Qemu-devel] [SeaBIOS] Re: Regression with floppy drive controller, Gerd Hoffmann, 2019/08/22
- Re: [Qemu-devel] [SeaBIOS] Re: Regression with floppy drive controller, Gerd Hoffmann, 2019/08/22