silverdr_at_inet.com.pl
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 silverdr@inet.com.pl 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...
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