ZX Spectrum > WSPÓŁCZESNE KLONY

AVR ZX Spectrum

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Lisitsin:
Additionally, videoCPU and central proceccor are different microcontrollers, so timings can be corrected independently.

trojacek:
IMHO, if you really want to make AVR to keep ZX timings, you'd better use any INT input and trigger it with the pixel clock divided by 224.

Lisitsin:
Interrupts is too long to exequte: 4 cycles to make interrupt, 4 cycles to return, 1 cycle to save status register ... For example, in my emulator fetch/decode/test for masked interrupt/increment R/jump to emulation routine is total 18 clock cycles. If it will be longer then 18 cycles system will be work slower.

trojacek:
Of course, if you find a software solution for this, it will be better (and cheaper).
I don't know exactly why your AVR produces inexact timings, but I would suggest you reading this page:

http://www.zxdesign.info/vidparam.shtml

and then the part "contended memory" of this document:

http://www.worldofspectrum.org/faq/reference/48kreference.htm

Lisitsin:
Very interesting! But most technical information i`v read in russian magazine "Radio". It was written about AVR ZX Spectrum too: https://dl.dropboxusercontent.com/u/12408899/Radio.zip

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