voidstar wrote on 2021-08-14, 23:33:

I was pretty sure I ran that old TDEMO.COM long ago on my Tandy 1000SX that had an 8088 (at either 8mhz or 10mhz, can't recall) - but maybe I'm mistaken and we had upgraded the PC by then.

Maybe that's the important difference. Your Tandy 1000SX was around twice as fast. As you experienced yourself, the 4.77MHz 8088 processor can not keep up with synthesizing music at 22kHz, but manages to get around 13 to 16 kHz, depending on the player. It is quite possible that the PC/XT is just too slow to run TDEMO correctly, even if the processor type itself is OK.

Well, I just tried TDEMO.COM inside 86BOX using SB configured at both IRQ5 and IRQ7 - and it worked fine. That's not complete proof that this isn't the issue (on why I can't run it on my 5150), but it's pretty good evidence and motivates me less to try that experiment (on the physical setup).

So yea, the third option is looking more likely: the 4.77mhz just can't keep up (that EGA GUI itself might just be too intense).

I remove that TDEMO.EGA file altogether to see what happens - TDEMO still runs without it, but you have to press ENTER shortly after it loads to get it going. Attached is what the screen ends up looking like (without the EGA file present). I haven't tried this on the physical machine yet, but I suspect it won't make any difference.
NOTE: pressing INS or DEL will snap the TDEMO settings between like XT and AT.

I've been exploring MODM and GLX more...

- GLX: backspace disables the spectrum, noticeably speeding things up in the playback
- GLX: spacebar lets you pick a new file even while the current file is playing

- MODM: although not documented, you can press DEL to erase files (handy for getting rid of files you don't like right away)
- MODM: spacebar pause the playback.

Can't you just replace the obsolete 8088 by something good, say a NEC V20 ?
I mean, sure, the V20 runs slightly out of spec in XT compatibles already, but maybe the Tandy isn't worse, so it will work as well ?
Installing a serious CPU would also enhance compatibility with normal DOS programs that were compiled with 80186/80286 instructions.
(The 8088 can still be stored in the old PC. A matchbox and some double-sided tape will help.)

Oh, I actually do have a V20, but for now choosing to keep with the original processor - as a kind of study of what works and what doesn't (on physical 5150 hardware).

But you're right - anyone who had added a SoundBlaster as early as 1989 probably had some sort of CPU upgrade (or a new PC entirely). Although, I can't really find evidence on how easy it was to order a V20 back then (like, could they be sold during the Intel lawsuit? were they under $200 and essentially affordable to anyone who could have also afforded a soundBlaster?).

I just came across an InfoWorld that list the NEC V20 being the same thing as the 8088-2, and the 8088-2 is what the Tandy 1000SX used.

I played around more with 86BOX. For one thing, TDEMO.COM does requires 512KB RAM. For any configuration I tried with 256KB RAM, the program just sits there (but no out of memory report). 86BOX won't let me give 512KB except until I pick the 1986 IBM XT or the Tandy 1000. Then within either of those selections, TDEMO.COM won't run correctly at 4.77mhz selection - it has to be at least 7.16 mhz. This is all per 86BOX.

As was mentioned earlier, maybe the issue is that @ 4.77mhz the stock processor simply can't load/process fast before it realizes new data is needed, so it's internally "stuck" trying to play the next track? Even at the 7.16mhz selection you can hear that it is struggling a little bit to keep up. (I suspect TDEMO is "locked" to a high playback, 18-22khz?)

Next weekend I may have all the parts I need to try making a cable to see if I can 4-disk drive support working (2 internal, 2 external). During that, I'll have the case cracked open and may swap in the V20 then. Maybe it's just enough extra "ooommf" to get TDEMO going even at 4.77mhz, but with that locked rate it probably still won't sound very good.

I think I recall getting modplay to pump samples out the PC squeaker at 5khz from a bogstock 8088, but dunno how heavily the CPU was loaded just with processing the mod, or how much of that playing overhead could be offloaded to a soundblaster.

So, just an update... I finished my 4-disk drive experiment. I did have the 5150 case open, but I held off on swapping in the V20 for now. I still want to see what the 4.77mhz can do - for example, I'm now exploring more about multi-tasking options (DesqView 2.25).

So related to this, I wanted to report something I realized about GLX: it is a great MOD player, I was reading through it's documentation, and I noticed it has a a SHELL TO DOS feature.

So I tried it out - and WOW, it makes GLX like a TSR. The music keeps playing in the background - AND you can run other (text) applications. I ran BEAST, a simple text-mode game. And the music kept playing. I also played PCPOOL -- which actually loaded and ran (in CGA), but when actually running the physics of the pool balls, the MOD playback slowed down significantly. Still, quite exciting that it worked.

So that's pretty neat - you don't need a fancy multi-task utility, GLX lets you do some casual computing while playing audio in the background (on a stock 4.77mhz 8088, with 640KB RAM). I could also view text files and do some simple file management. The only nit was the background audio was on loop, I couldn't see a way to specify a background play list.

I've started putting together various notes about my 5150 setup.

https://voidstar.blog/ibm-pc-5150-notes/

The audio specific stuff is here:
https://voidstar.blog/5150-setting-up-soundblaster/

MacOS and Linux and BSD are nice thing. but if you come form the DOS Windows OS/2 BeOS .... all other OS world, then two thing bother you, and they bother you mutch, ok the Unix derived "everything is a file" and "there are no drive letters" we can live somehow. But a file itself says what type it is, instead of extention, this is frustrating. Try to extract Stuffit executable in Windowns and then run it in MacOS and see what happens 😁