27 Jul
2004
27 Jul
'04
4:03 p.m.
On Tue, 27 Jul 2004, Steve Thatcher wrote:
besides the fact that it isn't possible to read sd
disks with a
controller that can only do dd.. so what does the diagnostic track read
function of the 765 do (given that it is trying to read dd data)?
At the risk of offending those who already know about it:
The WD type FDCs (NOT including NEC type FDCs made by WD)
have a track read command that reads every bit of the track,
separating data pulses from clock pulses, but doing little else,
although there are some complications in dealing with address
marks (which are bytes with missing clock pulses)
The NEC type FDCs, as are used on PC FDC cards, have a
"track read" command, but it does additional processing,
and strips out the headers, gaps, etc., providing you with
ONLY the data from within all of the sectors on the track.
I would prefer to call that a "multi-sector" read, not a "track
read".
The NEC approach is more convenient for some uses, but I'd
much rather have the "raw" track read of the WD type chips.
Actually, I'd rather have a TRULY raw read, and separate the
data and clock pulses in software.
The Central Point Option Board (and the CatWeasel) provide
the easiest ways to get that capability on a PC, unless
you build your own hardware.
There are also some neat things that you can do with the
disk access on an Amiga.