17 Jul
2005
17 Jul
'05
4:10 p.m.
Hi Jules,
On Sun, 2005-07-17 at 07:28 -0400, Dave Dunfield
wrote:
Thanks - I'm not sure this helps me, as the numbers given are different
than the NEC table. Here's what I have:
(Sector-size sectors/track GPL1 GPL2 - all numbers are in decimal)
GPL1 = gap-length when reading/writing
GPL2 = gap=length when formatting
8" FM:
128 26 7 27
256 15 14 42
512 8 27 58
1024 4 71 138
2048 2 200 255
4096 1 200 255
8" MFM:
256 26 14 36
512 15 27 84
1024 8 53 116
2048 4 153 255
4096 2 200 255
8192 1 200 255
5" FM:
128 18 7 9
128 16 16 25
256 8 24 48
512 4 70 135
1024 2 200 255
2048 1 200 255
5" MFM
256 18 10 12
256 16 32 50
512 8 42 80
1024 4 128 240
2048 2 200 255
4096 1 200 255
Clearly the 200/255 are the maximum values. I have tried working the numbers
without these entries, and still cannot come up with a calculation.
As you can see the gap sizes differ quite a bit from the ones that you have
documented - with the 765, this is only one of several gaps, and the controller
does not provide complete access to the raw format like a 179x controller
would.
I assume the gap sizes need to decrease for formats which have an extra
sector (or two) over the NEC table, however I do not know by how much ...
Any additional table entries, or information on how to calculate this would
be much appreciated.
If no calculation is possible, can anyone point
me at a more complete table of
suggested GPLs? The NEC table has some large holes, for example 9x512 and 10x512
are missing.
In case it's useful, I've got the following in the Torch Manta SCSI-
floppy controller documentation (amongst others):
512 byte sectors (5.25" or 3.5" media):
FM recording, 4 sectors/track, gap3 size is 175 bytes of FFh.
FM recording, 5 sectors/track, gap3 size is 31 bytes of FFh.
MFM recording, 9 sectors/track, gap3 size is 66 bytes of 4Eh.
1024 byte sectors (5.25" or 3.5" media):
FM recording, 2 sectors/track, gap3 size is 255 bytes of FFh.
MFM recording, 4 sectors/track, gap3 size is 255 bytes of 4Eh.
MFM recording, 5 sectors/track, gap3 size is 66 bytes of 4Eh.
512 byte sectors (8" media):
FM recording, 7 sectors/track, gap3 size is 149 bytes of FFh.
FM recording, 8 sectors/track, gap3 size is 62 bytes of FFh.
MFM recording, 14 sectors/track, gap3 size is 120 bytes of 4Eh.
MFM recording, 15 sectors/track, gap3 size is 73 bytes of 4Eh.
MFM recording, 16 sectors/track, gap3 size is 33 bytes of 4Eh.
1024 byte sectors (8" media):
FM recording, 3 sectors/track, gap3 size is 255 bytes of FFh.
FM recording, 4 sectors/track, gap3 size is 157 bytes of FFh.
MFM recording, 7 sectors/track, gap3 size is 255 bytes of 4Eh.
MFM recording, 8 sectors/track, gap3 size is 128 bytes of 4Eh.
can't remember what controller IC the board uses now though - I'm
reasonably sure it's not a 765. The Manta docs only talk about gaps 1-4, however I know
some of my Acorn
docs reference a gap5 which sits between the gap4 at the end of the last
sector on the track and the index marker - I have no idea what that's
supposed to do as it's listed as being 0 bytes long in the Acorn
examples!
Normally the last gap is filled from the end of the last sector until
the physical index mark occurs. The 765 appears to do this automatically
as part of the "Format Track" command. For a controller like the 179x,
you need to keep providing filler bytes until the physical end of track.
Regards,
Dave
--
dave04a (at) Dave Dunfield
dunfield (dot) Firmware development services & tools: www.dunfield.com
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