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Re: [Qemu-devel] Re: Qemu floppy emulation problems - partially solved

From: Fabrice Bellard
Subject: Re: [Qemu-devel] Re: Qemu floppy emulation problems - partially solved
Date: Sun, 03 Oct 2004 23:49:26 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.4) Gecko/20030624

Applied a modified version. Tell me if it works.


Derek Fawcus wrote:
On Wed, Aug 18, 2004 at 05:35:19PM +0200, Mike Nordell wrote:

Johannes Martin wrote:

1. diskette_param_table in rombios.c from Bochs is too short. It neeed two
more bytes, else e.g. NT believes the floppy only got 31 cylinders (the code
following the table begins with "push ds", 0x1e, and that just happens to be
"maximum track" NT expects). Append:
db 79
db 0

This is obvious if looking at the registry value
ppyDiskPeripheral\0\Configuration Data.

(x, y was 5 and 0 respectively on a real machine, but you might experience
local fluctuations)

Compare the last two bytes from a real system (working) with a non-working
QEMU-installed system.

Well that would seem to be an error in the NT code,  or we're triggering
something in the NT code which makes it seem to think there should be
a larger table.

The original table was only 11 bytes (as in the Bochs BIOS),  you can
look at the interrupt list to see.  It seems there is an enhancement
that adds an additional 3 bytes.

However from the layout of the BIOS,  it looks as if there is no room
to expand the table in place,  one'll have to have the param table pointer
(int 1e) point somewhere else.

Anyway,  I hacked something up if you want to try...

The diff is at http://www.employees.org/~dfawcus/rombios.c-diff,  and the
rom image is at http://www.employees.org/~dfawcus/bios.bin

I've not tried your other diffs yet.


Format of diskette parameter table:
Offset  Size    Description     (Table 01264)
 00h    BYTE    first specify byte
                bits 7-4: step rate (Fh=2ms,Eh=4ms,Dh=6ms,etc.)
                bits 3-0: head unload time (0Fh = 240 ms)
 01h    BYTE    second specify byte
                bits 7-1: head load time (01h = 4 ms)
                bit    0: non-DMA mode (always 0)
                Note:   The DOS boot sector sets the head load time to 15ms,
                          however, one should retry the operation on failure
 02h    BYTE    delay until motor turned off (in clock ticks)
 03h    BYTE    bytes per sector (00h = 128, 01h = 256, 02h = 512, 03h = 1024)
 04h    BYTE    sectors per track (maximum if different for different tracks)
 05h    BYTE    length of gap between sectors (2Ah for 5.25", 1Bh for 3.5")
 06h    BYTE    data length (ignored if bytes-per-sector field nonzero)
 07h    BYTE    gap length when formatting (50h for 5.25", 6Ch for 3.5")
 08h    BYTE    format filler byte (default F6h)
 09h    BYTE    head settle time in milliseconds
 0Ah    BYTE    motor start time in 1/8 seconds
---IBM SurePath BIOS---
 0Bh    BYTE    maximum track number
 0Ch    BYTE    data transfer rate
 0Dh    BYTE    drive type in CMOS

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