FDC Gap Length?

[Jules Richardson]

On Sun, 2005-07-17 at 07:28 -0400, Dave Dunfield wrote:
> 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!

cheers

Jules