RL02-USB Controller Status/Problem

John Wilson wilson at dbit.com
Wed Apr 8 23:05:47 CDT 2015

On Wed, Apr 08, 2015 at 08:55:31PM -0700, Don North wrote:
>(2) Logical mode. Your USB interface reads/parses the DEC STD 144 bad block
>table and does the appropriate revectoring of known bad blocks. On the host
>side you end up presenting what amounts to an RL02K-EF drive image.

DEC std 144 just lists the bad blocks, it doesn't revector them.  The RT-11
(only!!!) DL: driver does revectoring based on its own private table in block
1 (so hilarity ensues if the disk you're reading isn't an RT-11 disk).  But
that's important only because RT uses contiguous files -- all the other
OSes know how to avoid bad blocks cleanly so they don't need to live in
an error-free utopia.

I'd think the way to handle dumb host software is to log bad blocks somewhere
but return all zeros (or real data if that's possible), so at least programs
won't crap out part way through a copy.  But then you have to make sure you
read the error log before you assume it worked.

I'd love to hear the results of running this device with E11.  E11 does
pass error status through but other than with floppies, I don't get a lot
of chances to test those code paths.  A while back I added a layer which
inserts fake bad blocks on purpose, just for testing a wad of PDP-11
disk drivers I was writing.

John Wilson
D Bit

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