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Re: Minix 1.1 with QEMU

From: John Snow
Subject: Re: Minix 1.1 with QEMU
Date: Fri, 25 Sep 2020 13:27:38 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0

On 9/23/20 1:00 PM, Will Senn wrote:
On 9/23/20 11:53 AM, Philippe Mathieu-Daudé wrote:
Hi Will,

On 9/23/20 6:45 PM, Will Senn wrote:
Long time user, first time poster :)

So, I'd like to be able to run Minix 1.1 on my Macbook Pro mid-2012
w/16gb RAM (MacOS 10.14.6 Mojave). Qemu will run pretty ancient OS'es
such as DOS 2.0, which I use all of the time. However, I'm having some
difficulty getting Minix to run. I am able to boot the first floppy, but
when I change to the second floppy, the system freezes and I can't tell
what is going on. Here's what I did to get this far:

brew install qemu

qemu-system-i386 --version
QEMU emulator version 5.1.0

mkdir ~/workspaces/retro-workspace/minix-1.1
cd ~/workspaces/retro-workspace/minix-1.1
tar xvjf Intel-1.1.tar.bz2
cp Intel-1.1/floppy_disk1 ./Disk01.img
cp Intel-1.1/floppy_disk2 ./Disk02.img
cp Intel-1.1/floppy_disk3 ./Disk03.img
cp Intel-1.1/floppy_disk4 ./Disk04.img

qemu-system-i386 -drive
   -boot a \
   -no-fd-bootchk \
   -monitortelnet::2222,server,nowait  -serial mon:stdio

Qemu boots to the Minix 1.1 Boot screen and says to swap to floppy 2, so
in the monitor:
change floppy0 Disk02.img raw

I press l (el) and it scans the disk, lists the files on the disk and
reports no errors, but when I press =, it does a carriage return and
just sits there. I'm pretty sure this is the Minix going bye bye and not
necessarily QEMU, but I'm wondering if there is a way to see what QEMU
thinks it is doing or if it is what's hung? Usually, at this point,
Minix reads the disk contents into a Ramdisk and boots Minix.

You can turn on tracing! See docs/devel/tracing.txt for more. You can also run QEMU under GDB and break on floppy functions to see what's going on if you are so inclined.

Food for thought... Minix expects to run on an IBM PC (5150), IBM PC XT
(5160), or compatible, and therefore the I/O is written for whatever
floppy controller was extant at that time (I'm guessing here), so if
that's different than modern day floppies, I suppose this could cause
the problem I'm experiencing here. Is there a way to see the floppy
controller activity in QEMU? Similarly, I gather it expects a CGA
compatible monitor (EGA/VGA, etc should be fine).
Can you try adding '-machine isapc', which is closer to the 5150?

I appreciate your help on this.

Minix 1.1 works 'ok' in 86Box and other IBM PC emulations, so I know the
floppies are fine.



GPG Fingerprint: 68F4 B3BD 1730 555A 4462  7D45 3EAA 5B6D A982 BAAF


My new incantation is:

qemu-system-i386 -machine isapc -drive file=Disk01.img,format=raw,if=floppy,media=disk,readonly=off,index=0,snapshot=on -boot a   -no-fd-bootchk   -monitor telnet::2222,server,nowait -serial mon:stdio

with the same outcome :(. Thanks for the suggestion, I'll keep it in mind for other projects.


GPG Fingerprint: 68F4 B3BD 1730 555A 4462  7D45 3EAA 5B6D A982 BAAF

This isn't the first time I've seen a report of floppy disks behaving poorly in older operating systems.

I'm afraid I don't have the time to really investigate these issues, but I am happy to take patches.


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