x8086NetEmu discussion

[Anonymous]

Great to have a forum for this now. So, where were we? 🙂

[xfx]

Well, I guess it’s better than the Disqus system… but I find them a bit odd 😉

Anyway, I’m almost 99.99% sure that my problems are related to the MUL and DIV opcodes.
Don’t ask me why, as it’s just a hunch.

Would you know of some utility that could test these opcodes?

[xfx]

This is interesting.
So I start up the emulator and I leave it at the DOS prompt as I work on something else and completely forget about it.

An hour or so later, I go back to the emulator and this this what I find:

What gives?

[xfx]

hmmm… this is weird.
So if you run the emulator with DOS 6.22, after about 7-9 minutes it will start displaying the “Divide Overflow” error… non-stop.

But, if you let it run (displaying the divide error), for about 7-9 minutes, it will eventually normalize and work as if nothing had happened…

Then, after 7-9 minutes it will start showing the “Divide overflow” error message, again!

It’s definitely a cycle. Perhaps caused by a variable not being able to handle some “large” value… and eventually rolling over as if it was being bounded through a modulus operation.

Anyway, something I’ve learned while working on this emulator is that “extraordinary bugs” are often caused by “quite simple mistakes”.

For example, this bug with BASIC

was fixed by correcting the way the CPU flags are calculated for opcodes that depend on the Carry Flag (ADC/SBB/etc…).

I just wish there was some (probably Intel developed) utility that could test every single 808x opcode…
That would saved me so much time!

• This reply was modified 11 years ago by xfx.
• This reply was modified 11 years ago by xfx.
• This reply was modified 11 years ago by xfx.

[xfx]

Hi Mike.
I’ve been having some time off so I have worked a little bit more on the emulator.

But, despite having corrected tons of bugs, I’m still having the same issues with edit.exe and qbasic.exe (see the status bar):

No matter what I try, I just can’t find the problem.
So, I was wondering: would you happen to have some utility (or utilities) that might help me test the various aspects of the emulator, such as memory, registers, flags, opcodes, etc…?

• This reply was modified 10 years, 8 months ago by xfx.

[Author]

Posts