RL02K Pack Reliability/Characteristics

Christopher Parish christopher.parish at parishcomputers.com
Tue Mar 31 00:43:11 CDT 2015

>> Second, I've noticed that the drive seems to mis-seek on occasion.
>> [...]
> I assume you are aware of that any software driver for the RL drives
> needs to read the headers to verify that they are on the right track,
> after doing a head select (or rather a change in which head you have
> selected), and do a new seek if on the wrong track. Repeat until on the
> right track.
> Essentially, seeks on the RL drives are not reliable, and you must 
> always first check that you are on the right track before doing anything 
> else.
> I would almost suspect your controller is just fine in this aspect. 
> (This is documented in manuals, if you read enough.)
> Johnny

oops... That makes me feel a lot better.  I did design my controller to take the difference of the commanded track vs the observed track and send it to the drive, but I didn't know it was somewhat unreliable as to which track you will land on.  That's consistent with most of the data "corruption" I've seen.  Random tracks have duplicate data in them, but it's miraculously solved when the next track is addressed or when I move off of and return to that track.  That's because my FPGA always uses the last observed header to do its track difference calculation, but it doesn't check that the resulting seek is executed by the drive correctly.  The micro controller serving as the USB interface assumes that it will be returned data from the track it requested, which has proven to be false.

Those references to square root generators and kick pulses in the RL02 design documents scared me a little and should have clued me in that this isn't 100% deterministic.  Oh well.

Regardless, thanks for the info!

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