Sunday, March 5, 2017

Hercules Terminator 64 strikes back

This is how the S3-Trio64 story (the beginning is in the previous post) went on.

The monitor LED was blinking as if there was no signal, and it looked like after all my suspect was correct and a generic "vga-video-on" code was not enough to initialize a S3-Trio card.

I don't have a null-modem cable to debug OFW using a serial line, so all the instruments I had to debug what's going wrong were the "beep" and "reset-all" OFW commands. Which is not much. So I considered trying another emulators to verify my S3 OFW fix.

First I tried 86Box. Just like PCem it uses a ROM file name to determine whether a PCI card should be available for the emulation. So there is no official way to start it without VGA BIOS. But it's easy to hack: just rename a ne2000.rom to a desired VGA BIOS name. Then there is a network BIOS instead of VGA BIOS, which is harmless because it exits after not finding the network card. Yeah, 25 years ago I used my network card to read arbitrary ROMs, the story repeats itself in reverse.

The screen stayed black just like on a real PC, so I thought I've got an easy way to debug where it goes wrong. Although 86Box (just like PCem) don't emulate serial connections, still using a floppy image is much easier than writing a physical floppy. Alas, after some debugging it turned out PCem and 86Box don't emulate the PLL registers which was the reason why OFW didn't like it. Disabling the PLL restart took the OFW a couple steps further. Up to a 86Box crash, reported here.

Being desperate I even tried Microsoft Virtual PC, which supposedly emulates S3-Trio64. Well, it doesn't emulate the PLL, so I had to get back to the experiments with the physical card.

To make a long story short, the "vga-video-on" was not the problem. It seems that OFW supported only the most of S3 Trio64 and some of Trio64V+ chips.  I was just lucky to have an unsupported one. The OFW developers described the challenge of supporting the V+ chips in this nice comments:

   \ Problem: none of the above will have worked if this is a "Z" version
   \ of the Trio-64. "Z" versions are those parts marked with an "X" after
   \ their part number. Hey, I didn't make this up, S3 did. Anyhow, if you
   \ have one of these beasties, you have to wake up the part differently.
   \ The catch is, you pretty much have to do this in the blind because
   \ until the chip is working, you can't tell which version it is for if
   \ you go poking at a chip that is not awake yet, you may hang the system.

   \ As it turns out, the Trio-64V+ (which at this point in the probe process
   \ is indistinguishable from all of the other versions of the Trio-64, also
   \ won't have initialized prior to the above command. So, that extra command
   \ is usefull for both the "Z" Trio-64 and the Trio-64V+ (also known as the
   \ '765 [all other Trios have a '764 part number]). Oh but wait, there is
   \ more. The 765 does not respond to IO accesses unless the memory access
   \ enable bit is also turned on. Which is why the above now includes this
   \ "feature".
   \ And now back to our regularly scheduled programming...

So I tried to improve the Trio-64V+ recognition process, and Hercules Terminator 64 suddenly worked! The question is if the support of Trio-64V+ breaks the regular Trio-64.

I suspected my Trio-64V+ to be one of the last working ones in this Universe, but I wanted to be sure about it. After some googling I've stumbled over vogons.org, the community of people who still run S3 VGA (among some other cool stuff from the past) on a daily basis. So I asked them to test, and got a lot of responses. (Once again, thanks to everyone who responded)
Up to now there is no report of a Trio-64 which wouldn't work with the current OFW. So the fix is committed in the upstream OFW.

But still if you have one of  S3-Trio32, S3-Trio64 or S3-Trio64V+ cards, please test if they work with OFW, as described on vogons.org.

/Stay tuned for more S3-Trio adventures.

Saturday, March 4, 2017

AMD or NVIDIA? S3-Trio 64! (21+)

While on the Internet there are some hot discussions whether AMD or NVIDIA graphic adapters are better for virtualization, I think I'm the first one to pass thru a S3 Trio 64 VGA.

Well, I'm sure the regular readers of my blog are not just 21+, but probably rather 38+, and still under 90, so they can re what S3 Trio cards are. A casual reader may look it up on the Wikipedia. I can only say - it was very cool in 1995. And in 1997 I think all of my friends already got rid of the Trio VGAs (replaced with, you know, AGP and all this "modern" stuff).

Why S3 Trio? It was used in the IBM PReP machines. At least in IBM 7020 40p aka Sandalfoot. As you may know from my previous posts, Hervé is working on adding S3 Trio 64 emulation to QEMU, and it's still work in progress. I wanted to make sure it will work under OFW, so no proprietary IBM firmware would be necessary.

Boom! It turned out it has been broken in the OFW tree all the time since the sources were published - for more than a decade. No big deal - they are hardly existing (thought I). Made a trivial fix - use a generic "vga-video-on" instead of a chipset-specific one. It didn't work under qemu from the first attempt, because some S3-specific sequencer registers were not implemented, so I had to disable some extra checks. Then it worked. Meanwhile Hervé added the support of these registers, so it also works unmodified.

Probably it would have been a good idea to consider the project finished at this point. But I had already an experience where firmware and emulator were built based on the specs of each other and quite different with the real hardware (qemu-system-sparc and OpenBIOS till 2009, interrupt handling qemu-system-sparc64 till 2012 and so on). So I wanted an independent test, to make sure the generic "vga-video-on" good enough for the S3 cards.

Luckily I still had a Hercules Terminator 64 (S3-Trio64V+) VGA card lying in a basement. So I could check the firmware on the physical hardware. I don't have a PPC machine, but it's no big deal, because the OFW drivers are cross-platform. I've built a floppy with OFW for i686 (the OFW has all the necessary sources and documentation how to do it, thanks Mitch). Booted and got to the OFW "ok" prompt. It works, so the case solved, right? No! Since it's a "video-on", it might be that it worked only because it was initialized by VGA BIOS in the text mode. So I unterminated the Terminator:

Hercules Terminator 64, "unterminated"


The system beeped as if there were no VGA, but after me pressing F1 booted the floppy. The screen stayed black.

/ to be continued, stay tuned.

Sunday, February 12, 2017

AIX KDB under 40p

Some news on 40p emulation: it's possible to launch the AIX kernel debugger under qemu-system-ppc.  For some reason the current PowerPC 601 CPU frequency is limited to 7.81 Mhz in the upstream qemu, so it takes more than a hour to load the debugger. But with a small modification it gets to the point within seconds.

The command line:

$ qemu-system-ppc -M 40p -bios p12h0456.img -hda aix-5.1-cd1.iso -cpu 601

^^^ -cpu 601 is crucial. With the default CPU (604) it just hangs after a greeting.

 And after 90 minutes,  on the serial line....

AIX Version pinmore.c, s.@(#)65 1.1
Instruction Storage Interrupt - PROC
[kdb_get_virtual_memory] no real storage @ 646E6D60
KDB(0)> f
pvthread+000000 STACK:
WARNING: bad IAR: 646E6D60, display stack from LR: 646E6D5D
KDB(0)>
KDB(0)> dr
r0  : 00000000  r1  : 00595910  r2  : 00595C58  r3  : 00000001  r4  : 01C08180
r5  : 00000000  r6  : 00000000  r7  : 00000000  r8  : 00000000  r9  : 00000000
r10 : 00000000  r11 : 00000000  r12 : 646E6D61  r13 : 00606178  r14 : 000000B8
r15 : 00000020  r16 : 00000020  r17 : 0803004D  r18 : 005AF0BC  r19 : 003FED04
r20 : 00606178  r21 : 00000020  r22 : 00606000  r23 : 00003F50  r24 : 00003F48
r25 : 00003F3C  r26 : 00000000  r27 : 63683A2C  r28 : 00003A24  r29 : 00003A20
r30 : 00590C70  r31 : 00000000
KDB(0)>

It's a pretty neat debugger somewhat similar to Solaris kadb:

KDB(0)> dc main 40
.main+000000     mflr    r0
.main+000004      lwz    r3,36E8(toc)        36E8(toc)=NON_DEBUG_AIX
.main+000008     stmw    r30,FFFFFFF8(stkp)
.main+00000C      stw    r0,8(stkp)
.main+000010       li    r0,1
.main+000014      stw    r0,0(r3)            r0=00000001
.main+000018     stwu    stkp,FFFFFFC0(stkp)
.main+00001C       bl    <.kdb_init>
.main+000020       bl    <.hardinit>
.main+000024       bl    <.vmsi>
.main+000028       bl    <.hardinit_defered>
.main+00002C       bl    <.init_locks>
.main+000030       bl    <.init_anyother_locks>
.main+000034       bl    <.ios_init>
.main+000038       bl    <.kdb_pin_symtable>
.main+00003C       bl    <.debugger_init>
.main+000040       bl    <.kx2init>
.main+000044       bl    <.kmem_init>
.main+000048       li    r3,B
.main+00004C       bl    <.i_enable>         r3=0000000B
.main+000050       bl    <.k_protect>
.main+000054       bl    <.wlm_ccb_init>
.main+000058       bl    <.strtdisp>
.main+00005C       bl    <.epost>
.main+000060       li    r4,0
.main+000064      lwz    r3,13C4(toc)        13C4(toc)=kernel_lock
.main+000068       bl    <.lockl>
.main+00006C       li    r30,0
.main+000070      lwz    r3,37EC(toc)        37EC(toc)=init_tbl

/stay tuned

Saturday, February 4, 2017

PReP IBM 40p Emulation in qemu-system-ppc

Hervé Poussineau is doing a great job on improving PReP emulation in qemu. The initial patch series is getting merged into upstream master, but there is more in Hervé's git tree: http://repo.or.cz/qemu/hpoussin.git/shortlog/refs/heads/40p. I've built an OpenFirmware binary with SCSI support for it, and once Hervé improves S3 Trio emulation there will be a build with S3 support too.

Btw, the S3 Trio support in the Herve's branch is already pretty cool. Here are some screen shots of the boot process with the proprietary IBM firmware (it's really just the firmware, not an OS):

40p screen right after the reset

Other than IBM PC, an IBM PReP machine starts in a graphic mode with some animation, showing the initialization process.

Initializing devices

More devices...

All devices are found

Now the firmware tries to boot an OS or a System Management Services (SMS) disk:

F4 was pressed

Now there is a hidden but a well known feature. Instead of inserting a floppy, blindly type "eatabug", no quotes. For a tech person it may sound like "Enhanced ATA Bug", but I guess the pronunciation is "eat a bug". And this will open a resident monitor, which looks quite powerful (I still think OFW is more powerful though ;-).

Resident monitor help
 That's all about the 40p emulation for today.

/Stay tuned

Saturday, January 21, 2017

sun4v emulation is in qemu master

sun4v emulation patches were merged into QEMU master on January, the 19th. Directly from my git tree. So now I'm a real co-maintaier. ;-)