Date: 2005-11-13 21:00:47
On 2005-11-13, at 14:17, Spiro Trikaliotis wrote: > Hello, > > * On Sat, Nov 12, 2005 at 03:17:29AM +0100 firstname.lastname@example.org wrote: > >> 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? > > The 1541 uses a clock of exactly 1 MHz. The fastest bit rate is > (16/13) > MHz / 4 on tracks 1-17 (according to > http://www.zimmers.net/anonftp/pub/cbm/schematics/drives/new/1541/ > service/Page_07.html), Ah, there's the table I was looking for! FYI I wasn't _that_ lazy. I visited zimmers and even dloaded the whole GIF based manual in search for this info. Just somehow thought the HTML was only a different form of the same data. Thanks for that. > the clock generator gets (16 / 13) MHz = approx. 1.2307 MHz, and > according to the schematic on > http://www.zimmers.net/anonftp/pub/cbm/schematics/drives/new/1541/ > service/large/Page_11.gif, > this clock is divided by four. > > Thus, you have (1 MHz / (16/13) MHz) * 4 * 8 = (13/16) * 4 * 8 = 2 > * 13 > = 26 cycles for writing out on tracks 1 to 17. OK. That's it! > For reading in, you might > have less (as the clock is not derived by the 16 MHz used to drive the > processor, but from "what is on disk", which might be faster than what > you expect. Yes, I know. That's why I want to put some contingency in, while still assuming that 5-7% of speed difference/fluctuation should be the limit. > > This is not the complete story. These delays accumulate. Thus, if you > are "early" in reading one byte, you can be "late" in reading the next > one. For example, Wolfgang Moser has done systematical tests and he > found out that 41 cycles can still work, IF DONE PROPERLY. (!) I am not sure if I understand this... Also if e.g. my drive rotates on average some 5% faster than the one, which wrote the track - how can it be that? -- Spectrum rulez! - Vid Strpic at h.c.c Spectrum je smece gumicasto, commodore je najbolje mikroracunalo tog doba! - Damir Tubin, theretoo... Message was sent through the cbm-hackers mailing list
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