DEC RK11-C Disk Controller - on ebay...or is it?

[Fritz Mueller]

> On Feb 9, 2021, at 9:27 AM, Noel Chiappa via cctalk <cctalk at classiccmp.org> wrote:
> ... the Unix V6 RK pack formatter ...
> sets _both_ 'Format' and 'Read/Write-All', and _doesn't_ set up the sector
> header words in the memory buffer, arguing that even with 'Read/Write-All' on,
> the hardware is still generating the sector header word contents.

That's quite interesting!

I have experimented with Read/Write-All, but just for reads.  Basically, you set up the read and after the index pulse you get the bitstream from one surface of an entire cylinder in memory, repeating, inter-sector gaps, sync bits, header bits, etc, until the word counter expires.  Bit alignment of the stream wrt. memory buffer is in effect arbitrary.

To use the resulting data, you have to detect the sync bits, align the data, parse off the sector headers, etc.  In at least one case of attempting to recover a pack, I had some sectors that would consistently return read errors and no data; by reading entire cylinders in "all" mode and fiddling with the data alignment I was in fact able to recover the greater portion of the data in some otherwise inaccessible sectors.

  --FritzM.