![]() Tried to link in the libcsud.a library to get USB keyboard input but it slows down the ZX81 keyboard/display routine too much. I now have a 64usec timer triggering each scanline but the instructions are executed way faster than the original Z80 so I need to count them to make sure there are no more than 'x' instructions/NOPs per scanline. Also a (famous) demo called GUUST FLATER seems to run but the whole screen is compressed into the top 4 scanlines or so There must be some trickery going there to fool the original ULA into not updating the scanline counter. On testing some HiRes demo's I found the '25th anniversary' demo runs but the screen is not properly synced. ![]() I can use 5 GPIO pins for a joystick interface, just need to make a cable. Later on I changed the joystick interface to be ZXpand compatible. Since the real ZX81 was not designed to take more than 16k there is still room in the memory map to place some IO, for testing my joystick interface on the mbed version I had placed a pseudo register at 0xFFFF. If you were cunning, you would map it to ports including 31, and 5 of the GPIO pins would 'just happen' to provide a Kempston joystick interface hahaha. ![]() ![]() I seem to recall always having to write little machine code things in a REM statement to do the OUT instruction! Whichever memory locations you choose, they won't be available for RAM any more (obviously). Poglad wrote:That's true, although traditionally it was never done that way. ![]()
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