Date: 2005-11-12 03:17:29
On 2005-11-11, at 21:22, David Wood wrote: >>> No, there aren't enough cycles to decode to nybbles in realtime, >> >> Could you remind me how many of them are there in the worst case? > I know its offtopic and we all love to hate apple, ;-) In EU we hated Spectrums... :-) > but I read some > interesting information in a hardware reference book. There's a > GCR nybble > exactly every 32 cycles. There's no byte ready line or other hint > that a > nybble was read. Just read, and -exactly- 32 cycles later, read > again or > miss a nybble. :) Interesting. And how the first one was synchronised? > > The 1541 uses a variable bit clock, so it can vary, but the > smallest sector > count matches the evil system at 16/track, so it's probably not far > off. ;-) > It is probably not far off the "evil system" but I'd like to be more sure... I understand that I have as much time as it takes for the next byte to get shifted-in. Now this depends on bitrate so with the fastest bitrate there will be the least time to do anything. Adding few percents of contingency would give me safe result. I recall I did those calculations some ages ago and I _think_ it was something like INT( (cpuclock/fastestbitrate) * 8 * (1 - 5%) ) As long as I didn't screw something, it should be enough to know the fastestbitrate and the cpuclock numbers, which I don't remember ATM. AFAIR the 1541 had slightly faster clock than the (PAL) 64 but the bitrate? 320kb/s? -- We do not inherit the earth from our ancestors, we borrow it from our children. Message was sent through the cbm-hackers mailing list
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