HP 7970E - interest to split?

Paul Koning paulkoning at comcast.net
Fri Sep 29 11:52:19 CDT 2017

> On Sep 29, 2017, at 12:33 PM, Jon Elson via cctalk <cctalk at classiccmp.org> wrote:
> On 09/29/2017 10:56 AM, Henk Gooijen via cctalk wrote:
>> On a related note my plan is to make a USB-based, Pertec-compatible
>> controller for it. Not sure how SimH connects with peripherals so I'm
>> /very/ eager to talk with someone familiar with its workings. I'll also
>> release all the board files and firmware as open-source. Timeline as always
>> is completely unknown, though I do have a now-vested interest in making it
>> work.

It looks like it only handles tape container files (.TAP files) right now.  But the machinery basically has a tape emulation module (sim_tape.c) which has a number of functions roughly corresponding to what a tape drive does (read forward, write tape mark, rewind, etc.).  It doesn't look like a terribly hard task to support a real tape drive as another "container file format".  One question I can think of is how OS-dependent raw SCSI access is.

The approach would be somewhat similar to the disk support in SIMH, which does already have "RAW" as one of the formats, meaning direct access to a real disk.

> MANY, MANY years ago I got a surplus Pertec key to tape system that had a 7" 9-track 800 BPI NRZI drive connected to hardwired logic. You could key in data, verify data by re-keying it, and read back data to a panel of light bulbs.  It had core memory for the data buffer.
> I found the right place to slice the sections apart and have what was pretty close to the unformatted Pertec interface.
> I then wrote a mostly software-driven interface to read and write tape blocks on my CP/M Z-80 system.  I created tapes and took them in to work to map them and got it to write ASCII text files in VAX ANSI-D format.  It really was not that complicated.  This was a read/write drive with only a single data gap.  So, to write and check a record, you had to write it, back up and read it.  I used it for making backups.
> I think you could use a Beagle Bone and the PRU microcontrollers in it to do a Pertec unformatted interface.

I wonder if a BBB is fast enough that you can just drive the Pertec interface directly from the GPIO pins.  At 1 GHz lots of things become possible in software...

I noticed there is a BB "Cape" (I/O board) with a medium size FPGA on it.  Haven't found a use for that yet, but it looks pretty powerful for those case where software isn't quite fast enough.


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