Hrm, see my reply here last night disappeared into the void that is a 500 error (oddly the one in the other thread made it)
It's a bit unfortunate that it's not doable yet but I'm sure I can wait until the new firmware appears, even with the limitations you describe it should be very useful (although the 20us window is a bit concerning)
Port decoding, realise that, looked at the pinout again and see the pins for the signals you mention, thanks, makes a bit more sense now as to how it has two independent address spaces on the one bus...
The interrupt issue isn't really one as I was planning on just polling anyway -.o;
Kempston joystick should be easy enough even with those limitations since it'll just set/clear the bits depending on the position so when it's read it'll be fine, wouldn't need to use one at all but the keyboard reading is seriously limited (INPUT), even if I were able (in assembly or by accessing the channel directly) to read the keyboard, the terminal based nature of it would present other problems for games (although it'd probably be fine for non-game apps)
Given the limitations you mention, audio might be more of an issue, the audio playing bit would be fine as like the joystick it'd be set or clear when it's read as needed, actually getting commands to the chip for the audio is going to be troublesome if the value output is set only for 20us though, I have no idea if a PIC is even fast enough for that -.-, would quite like an SP0256-AL2 as well as the monophonic audio (perhaps as an option) for speech old school style :> but I have no idea if it'll be possible to read the data fast enough, some damn tight assembly might be required, lol
One other minor issue is the serial, will there be a way to disconnect the on board serial once the system is running so it'd be possible to for example load basic from SD then switch control to the TTL lines on the expansion header, to use a real terminal for example? (not that I have any left, I had like 6 DEC VT102s and they were lost in a move -.-)
At least the caveats make things tricky but not impossible, should be doable given I'll be designing for the micro rather than the original Altair...
Anything I do produce will be in the form of an open design anyway, not being John Kortink I have no intention of actually selling things at a profit, lol, but making an interface or few for this machine will be a good starting point before designing a computer from scratch (as I intend to one day -.o;), while I've been programming for many years (started doing Basic and Z80 on a 1K ZX81), the electronics is somewhat more recent.
Thanks for your help! much appreciated
