Oh - you made a thread for this
I think the most important thing of all, is supporting absolute address booting of the first sector instead of the PCE's index 01 method. Seems the stupid pressing houses can't figure out how to set index 01 to the correct sector
This would allow you to boot from an ISO9660 image.
Here are the main features that would be great and still have that PCE/TG feel(order of importance):
- Port based setup like the AC card did would be great. You could have up to 8 ports memory mapped on the hardware bank and could be programmed to point *anywhere* in the hucard address range. There's nothing like saving code/complexity and cpu cycles like free auto increment/decrement I/O port based accessing. That's like having 8 hardware indirect registers but with 21bit address range. Each port should have a Bank number associated with it too like the AC card. Making it compatible with the block transfer instructions.
- Simple single channel PCM DAC with volume setting. Standard 8bit version. You set the frequency and which buffer to read from. You wouldn't need much room, just maybe two 512kbyte buffers. The output could be on the audio input pin of the hucard port. It'd be great for things like samples or mono style instruments.
- External interrupt for a finer TIMER value. Maybe something that could even be in sync with hsync (you'd have to reset the TIMER on the first scanline VDC interrupt to resync it).
- 16bit/16bit -> 16bit MUL and DIV support. Port based of course, just like the SNES one. It help make coder cleaner and more convenient. Something under 10 clock cycle time.
A Bonus feature could be:
- Switch into all RAM mode for banks $00 to $7F. You could do this from main ram (bank $F8). Basically you could run any hucard/rom from a CD that's 8megs or less (or an all RAM with the SF2 32megabit address banking system - yeah I know it only *used* 20megabits). This would also allow for different/custom system cards to be dynamically uploaded into RAM(it would be lost on power off).