Tuesday, November 10, 2015

Work on DMS distribution project and mag tape interface


I decided to pick up an NCR5380 chip and interface it to an fpga, allowing me to drive the 9 track tape drives I own. This will be part of the SAC Interface Box, implementing the tape drives as IBM 2415 drives attached through an IBM 1133 multiplexer box with the Selector Channel RPQ,  the multiplexer box hooked to the 1130.

I have to create a PCB for the NCR chip and other circuitry to connect it to a Spartan 3E fpga. The fpga I am considered is connected by my fast link to the central ztex fpga board in my interface box.


I researched the checksum process used by the loader and DUP and created a subroutine to allow me to calculate a checksum to punch in the card decks I will create from the SLET phases on my disk cartridge. Having ensured the checksum is working properly, I went on to write the larger routine to take a SLET entry and read the phase it points to into a buffer.

Those subroutines in turn are called by code that reads the SLET, phase by phase and for each calls my reading routine. The final bit of code will be the subroutine to convert a buffer read from disk to card images appropriate for use n the System Initialization/Reload process.

I found some files online that are described as DMS V2 R11 card trays - but the format of the files aren't known. There is a decent chance this may be the full card decks I am recreating - a third view of them to help me triangulate on the canonical version,. At the least, I may be able to recreate the sector break card text that is missing from the IBM1130.org recreated files - and missing for the decks that I don't have in my trays.

Some sections appear to encode the card columns with rows 12 down to 9 left justified in a word, which would leave the low nibble of each word as 0x00, but there are other sections where it is 1130 object code pure and simple, with nonzero values in all nibbles of each word.

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