ps136sag@sdcc13.ucsd.EDU (John Ogawa) (04/25/87)
[eat]
Here's the answer to the seek rate problem I had earlier. Thanks to
Gerry W. for giving me the answer about seek/step rates and Jinfu
Chin for giving me the way to set them.
Here goes:
First, some info about disk access rates. Seek rates are the
same as step rates. This is the time for the head to move
across the disk (powered by the stepper motor), seeking for
a new track. This can be set either from a low level FDC
(Floppy Disk Controller) call, or a mysterious memory
change. I'll use the latter, since it's easier.
Apparently, there is a location (0x0A08) that contains the
current seek rate. This location is one WORD long. It
contains the seek rate for Drive A. Drive B's seek rate
(such as it is) seems to be at location 0x0A0C. The seek
rates are coded as follows:
0 = 6 msec
1 = 12 msec
2 = 2 msec
3 = 3 msec
To change the seek rate, just change the location. I use
MWC's POKEW call.
What about the documented, 0x0440 location? Well, I ran some
tests after changing the 0x0A08 location and found no
changes to the 0x440 location. Geez. I have no idea what's
with 0x0440! So, just in case, when I change 0x0A08 I also
change 0x0440.
There you have it. My apologies to Atari if this is considered a
mighty hack. It works, and nothing else seems to. Oh well.
My desk accessory is humming along now. I'm taking suggestions or
information if you want to give them :-).
John Ogawa
NET: ...ucbvax!sdcsvax!sdcc13!ps136sag
or
ps136sag@sdcc13.ucsd.edu
GEnie: TUSHIE