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Posted By

gerliczer
on 2009-01-05
12:23:08
 Re: TED-gurus, help me out (stable IRQs, FLI, 4x4 mode etc.)!

The number of CPU cycles per rasterline varies a lot depending on the CPU clock mode (single or double clock) and TED operation (border, normal line, badline). In double clock mode there are 109 in the border, 65 in normal lines and 22+3 in badlines. In single clock mode there are 57 in border, 57 in normal lines and 14+3 in badlines. The double clock/single clock mode roughly works through TED allowing the CPU to step its inner state either in every or every second clock cycle. Someone should upload here the old plus/4 mailing list's messages. There were a very detailed post by Crown about this.

Making an interrupt in every 4th line for a 4x4 mode may be an overkill. Making it in every 8th line in the middle of the char row should be enough, passing the char row boundary makes TED changing some necessary pointers anyway.

Trying the debugger of YAPE and plus4emu also may help understand how these things work.

I hope that this will help.



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