Wednesday, September 30, 2015

New disk drive coming, plus thinking about tape and disk support for SAC Interface Box


I boycotted the spring today.


I found an auction for a drive, similar to my Pertec, that appears to be new, as shipped by the maker and still on its shipping skid. I made an offer which was accepted and expect to receive the drive next week.


I have some design choices to make in order to finish up the remaining IO devices I might put on my system. The various disk drives (Diablo, Pertec, Perkin Elmer, and DEC) all have well defined interfaces that I can manage from an FPGA connected over the high speed link. What is harder will be to drive the two SCSI based tape drives.

I don't want to have to model a SCSI host in the fpga myself - too much work to be worth it - but there are ways I can use an intermediate. First, I could build a board around the NCR 5385 SCSI chip and NCR 8310 driver/receiver chip. Second, I could create an ISA bus from an fpga on the high speed link, then insert and drive a SCSI card. Third, I could find a small PC with SCSI support that would control the tape drives, communicating with it over an easy to implement common protocol such as parallel port. Fourth, I could drive the tape devices from the same PC that runs my Python program,

The NCR chip would require that I study and master that chipset to use it. The ISA bus requires me to implement that plus drive the SCSI card - I would need one with good documentation or a source code version of the driver. If I drove the tape units from the same PC, then the Python program could control them and pass the data. It would be similar to the virtual devices I implement already, except that it would use real tape drives rather than PC files as the source of the data.

I am collecting data on the NCR chips, ISA bus and various driver cards, to help me make the decision. I will also research Python support for SCSI devices. The downside of running on Windows is that SCSI support is ugly and poorly documented, whereas Linux has good support.

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