undefined | Better HN

0 pointsexikyut8y ago0 comments

Hmm.

According to the DOSBox debugger, it gets stuck in an infinite loop poking/polling interrupts:

  278407: CPU:Illegal/Unhandled opcode 63
  278408: CPU:Illegal Unhandled Interrupt Called 6
  278410: CPU:Illegal/Unhandled opcode 63
  278411: CPU:Illegal Unhandled Interrupt Called 6
  278413: CPU:Illegal/Unhandled opcode 63
  278414: CPU:Illegal Unhandled Interrupt Called 6
  278416: CPU:Illegal/Unhandled opcode 63

I wonder if the DOSBox developers are aware of this, and if you could interest them in fiddling around to see what the cause is. It could be something very simple.

(Based on the fact that D86 was last updated in 2000 I doubt the author is going to be too interested in tinkering with it.)

---

HOWEVER!

D86 works just fine in QEMU - and, even better, if you use a CPU idle program for DOS to make QEMU not chew 100% of one core, the idle program will continue to have an effect even while D86 is running.

This being said, I have no idea how to use D86 :) and so cannot say whether an idler program will impact anything.

I tested with the IDLE.COM in "VMAdditions.iso" (date 3 Aug 2004, cksum 281796710). The program is so small (128 bytes FTW) that I see no issue with just

jMiO2DHAjsAmoaAAo/wAJqGiAKP+AIzIJscGoABAASajogC6GAC0Mc0huuIIkCCIdDO67giJdCu6+oECCIp0I/ v0+i7/LvwAqUgSCI2iuh4IkACOdAu6Zgj/dAO6KlDpQIE6ybo2UOg0deir/nIFA4Ctfv/DtE2/3s0YnXVARIc=

so you don't have to go index-of-/-hunting (you can just `base64 -d > idle.com` instead). I don't think whoever wrote this will mind :P

(Deliberately not using monospace for the block above to make things less visually jarring)

0 comments

2 comments · 1 top-level

nybblesio8y ago· 1 in thread

I haven't tried QEMU but I have successfully run D86 under an MS-DOS instances running in Virtual Machine and Parallels. However, these environment aren't well tuned for games and sound emulation is more or less useless.

My guess is that the author of D86, Eric Issacson (http://www.eji.com/), made use of some of his inside knowledge from his Intel days. Specifically, I know he liked to use encodings of the AAM instruction with bases other than 10. Intel didn't document the opcode properly so history records it as only supporting base 10, but it in fact can support quite a few number bases. Anyhow, I would speculate that DOSBOX doesn't support such a flexible interpretation of the encodings and that's why it's throwing illegal instruction exceptions. Maybe I should patch DOSBOX on stream sometime and submit the patch to the maintainers.

exikyutOP8y ago

> My guess is that the author of D86 ... made use of some of his inside knowledge from his Intel days.

I continue to be amazed at the amount of backward-compatibility inside the average Intel x86 CPU. If something stays out of long mode, it can still do all of that. Impressive, really.

And... I hadn't thought through to the point of considering what you were using D86 for :)

I agree, things like sound emulation leave a lot to be desired. I only use QEMU for its networking and HW-accel virtualization - DOSBox runs rings around it with eg Win3.1...

Have you tried PCem and 86Box?

> Maybe I should patch DOSBOX on stream sometime and submit the patch to the maintainers.

Now that would be really awesome. :D

j / k navigate · click thread line to collapse

278407: CPU:Illegal/Unhandled opcode 63 278408: CPU:Illegal Unhandled Interrupt Called 6 278410: CPU:Illegal/Unhandled opcode 63 278411: CPU:Illegal Unhandled Interrupt Called 6 278413: CPU:Illegal/Unhandled opcode 63 278414: CPU:Illegal Unhandled Interrupt Called 6 278416: CPU:Illegal/Unhandled opcode 63