Spectrum Computing

Dr beep wrote: ↑Thu Mar 26, 2020 9:37 pm 1) to keep code smaller I only want to use the IM2 table as if no hardware is attached (FF). Will this do or is due to some hardware a full table needed?

Dr beep wrote: ↑Thu Mar 26, 2020 9:37 pm 2) The emulator is now fully coded in upper memory (>32k). What are the speedeffects of coding or storing tables in lower memory (contented memory)? I will need this part of memory but at this moment I can either store tables which are read once on each opcode or screentables and intruptroutine to be executed more times per second. I want the fastest program possible. Loading and saving is stored here too, but that is no issue during emulation.

PROSM wrote: ↑Fri Apr 03, 2020 1:30 pm

Dr beep wrote: ↑Thu Mar 26, 2020 9:37 pm 1) to keep code smaller I only want to use the IM2 table as if no hardware is attached (FF). Will this do or is due to some hardware a full table needed?

It is widely assumed that you can't guarantee what will be on the data bus when the interrupt occurs, so for safety, you'd be best off generating a full table. Since the LSB could be set or reset, you should make each byte the same value, hence your interrupt routine's address should have identical high and low bytes.

Dr beep wrote: ↑Thu Mar 26, 2020 9:37 pm 2) The emulator is now fully coded in upper memory (>32k). What are the speedeffects of coding or storing tables in lower memory (contented memory)? I will need this part of memory but at this moment I can either store tables which are read once on each opcode or screentables and intruptroutine to be executed more times per second. I want the fastest program possible. Loading and saving is stored here too, but that is no issue during emulation.

When accessing contended memory, the CPU is made to wait whilst the ULA fetches the data it needs (more detail here). If you must use it, then you would be best just storing data there rather than code, as less contended reads will be required, and thus less delay will occur.

If I understand your post correctly, you have the loading and saving code stored in contended memory, but it works correctly. If that's the case, your emulator probably doesn't emulate contended memory, and for the purposes of debugging, you'd be better off trying something like Fuse or Spectaculator.

Bear in mind that you cannot store the IM2 table here, as otherwise ULA snow will result (more information here).