Well, given it's been a month since my last post so I thought I'd add a little update
After some more prodding through my emulator firmware, I managed the following enhancements to the 'virtual PC core'
1.) I added the once-popular 320x200x256 VGA/MCGA 'chunky mode' (aka mode 13h) to the list of supported graphics modes into the emulated BIOS and display controller. The only real restriction here is color palette being 'fixed' at 256 colors (output DAC assignment is 3/3/2-bits R/G/B respectively) and even the order of those fixed positions cannot be altered (at this time). That said however, it works and as a result some VGA games now also run in addition to Tandy Graphics/CGA supported games. Screenshots:
Elite Plus -
Title Screen Player ScreenSU-25 Sturmovik flight sim demo -
Player ScreenGobman (PacMan clone by filipe mateus) -
Title Screen Player Screen'SLIQ' from the PC demoscene era -
Utah TeapotTo allow some of the games to run at an acceptable speed, I decided to push the virtual system to it's highest possible limit on this 8-bit MCU made the core run to an equivalent speed of 1075 v1.1 Dhrystones (i.e. going into 80286 country..). This was achieved using some inelegant display hacks and an overclocked core..
Using SRAM instead of SDRAM for system memory should fix this problem and also take the system to say, well beyond 3000 Dhrystones without overclocking.
QBASIC compiled programs now run quite happily on this thing, but the speed of some runtime files, particularily those needing FPU support isn't blistering (the 'SLIQ' demo for example runs but is terribly slow, mainly for this reason). I've had more successes speed-wise with the C/C++/Assembly demos.
2.) Parallel port daughtercard: The artwork for this is also ready, which will use a CPLD (
view artwork), though I cannot build it until I also do the artwork for an SRAM version of the mainboard (which will include an expansion header for the daughtercard).
Well, that's it from me for now.. I hope to put up another Youtube video demo on the VGA-related stuff shortly.
Cheers and enjoy!
Valentin