10 Apr
2007
10 Apr
'07
10:28 a.m.
On 4/10/07, Chuck Guzis <cclist at sydex.com> wrote:
On 10 Apr 2007 at 3:24, Jules Richardson wrote:
That's how the Amiga trackdisk.device does it... turn on the motor,
slurp up a few thousand bits, then go looking for the first header.
It does help that there's a set of blitter terms to convert MFM to
binary and back using spare cycles from the graphics co-processor.
I suspect it's just to read disks that
don't start the track at the index
pulse (I'd wondered the same thing until his post about Amiga floppies).
The buffer on the CW is large enough to record much more than a
single revolution of a diskette, so when dealing with diskettes of
this type, I fill it up with larger sample. Decoding then proceeds
with the first good (complete) sector in the buffer. I don't even
bother to pay attention to the index pulse in this case--I just allow
a certain amount of settling time after seeking and begin recording
for a sufficiently long time to grab about a rev and a half.
I can
t quote chapter and verse for the exact amount of excess rotation that
trackdisk.device does, but anecdotally, I recall 1.1 revolutions.
-ethan