|Re: [hatari-devel] HD floppy timing|
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Le 30/05/2016 17:37, Roger Burrows a écrit :
Hatari appears to support HD floppy images; that is, you can attach a .ST file
with 18 sectors/track and it reads it OK. However, the timing appears strange.
I'm doing some read tests under EmuTOS (because floppy access on real hardware
seems slow), and tracing the timing internally in EmuTOS by storing start & end
times for each floppy operation. AFAIK, the speed of the drive is 300rpm, i.e.
5 revs/second, or 200 msec per revolution. I'm using a recent development
version of Hatari (May 19 2016) and starting with --machine falcon.
Because the test program is just doing floppy reads, you would expect the end
time for reading a sector to be the same as the start time for the next sector,
and it is. So the program itself is not causing any delays. However, the
total time to read a sector is 21 clock ticks, i.e. 105 milliseconds, which
seems strange. If we are hitting consecutive sectors, it should be around 10
msec; if we have a miss, it should be around 210 msec.
This is not a big problem, and I assume it may be because the drives don't
really emulate HD drives internally. But I thought I'd mention it as something
that could be improved in the future. Meanwhile, I'll go back to real hardware
I never really checked the accuracy of HD/ED format, since no program is
known to depend on this (it's not the case for DD where game protections
expect very precise timing for gap, read sector and so on).
Basically, DD timings to transfer a byte from floppy are divided by 2
for HD and divided by 4 for ED.
It's quite possible this doesn't give the same values as real HW :)