Interesting, what kind of ESDI controllers do you have? They got
advanced features like cache, ordered seeks, and burst mode/block mode DMA?
C
On 4/18/2022 6:09 PM, Douglas Taylor via cctech wrote:
Because of this I'm holding on to my DEC Qbus ESDI controllers!!! You
never know....
Doug
On 4/17/2022 4:35 PM, Guy Sotomayor via cctech wrote:
I chose ESDI and SMD fundamentally because the interface is 100%
digital (e.g. the data/clock separator is in the drive itself). So I
don't need to do any oversampling.
TTFN - Guy
On 4/17/22 11:12, Paul Koning via cctalk wrote:
On Apr 17, 2022, at 1:28 PM, shadoooo via cctalk
<cctalk@classiccmp.org> wrote:
hello,
there's much discussion about the right method to transfer data in
and out.
Of course there are several methods, the right one must be carefully
chosen after some review of all the disk interfaces that must be
supported. The idea of having a copy of the whole disk in RAM is OK,
assuming that a maximum size of around 512MB is required, as the RAM
is also needed for the OS, and for Zynq maximum is 1GB.
For reading a disk, an attractive approach is to do a high speed
analog capture of the waveforms. That way you don't need a priori
knowledge of the encoding, and it also allows you to use
sophisticated algorithms (DSP, digital filtering, etc.) to recover
marginal media. A number of old tape recovery projects have used
this approach. For disk you have to go faster if you use an existing
drive, but the numbers are perfectly manageable with modern hardware.
If you use this technique, you do generate a whole lot more data than
the formatted capacity of the drive; 10x to 100x or so. Throw in
another order of magnitude if you step across the surface in small
increments to avoid having to identify the track centerline in
advance -- again, somewhat like the tape recovery machines that use a
36 track head to read 7 or 9 or 10 track tapes.
Fred mentioned how life gets hard if you don't have a drive. I'm
wondering how difficult it would be to build a useable "spin table",
basically an accurate spindle that will accept the pack to be
recovered and that will rotate at a modest speed, with a head
positioner that can accurately position a read head along the
surface. One head would suffice, RAMAC fashion. For slow rotation
you'd want an MR head, and perhaps supplied air to float the head off
the surface. Perhaps a scheme like this with slow rotation could
allow for recovery much of the data on a platter that suffered a head
crash, because you could spin it slowly enough that either the head
doesn't touch the scratched areas, or touches it slowly enough that
no further damage results.
paul
