IBM 1410 FPGA: Diagnostics!!!

With the console typewriter working, and the ability to load core images, I was now ready to try and run some diagnostics. The first issue I ran into was that the main diagnostics, CU01, was initialized for 80K of core. That the core image file was larger wasn’t an issue: the Windows based support program knows to only send the first 40K. However, there was a flag denoting machine size that needed to be “patched” — which I did using my emulator, and then saved as a new core image.

Loading the diagnostic, it typed out its identifier, but then quickly errored out with an Assembly Channel error on a Subtract instruction where the destination B-field was initially positive, but turned negative during the subtraction. This was not the first place I expected to see an issue – figured it would more likely relate to some trigger or other. But nope, this was a simple issue in the Assembly Channel.

The problem arose because the ALD diagrams I have are mostly for an IBM 1410 with the Accelerator special feature, however, most of the ALD diagrams for the Assembly channel proper (ALD 15.50.xx.1) are for the non-accelerated version whereas the Assembly channel controls (ALD 15.49.xx.1) are for the accelerated version. There were several signals that ended up either not being used, or having no source as a result:


These all relate to cases where the B field ends up with a sign other than its original sign. I suspect that the idea was that these signals provided earlier gating to the assembly channel rather than just deriving them from the adder with additional gate delays.

After fixing the Subtract issues which involved just the “B” bit on page, (going from positive to negative) I immediately ran into the same issue on the first pass of the diagnostic during the same test, changing from negative to a positive result. Fixing this involved pages (mostly). As a result the pages for the Assembly channel have some gates who’s note at the top is “FUDGED”. 😉

With that, so long as I didn’t enable I/O overlap and Priority Alert (interrupts) during the test, CU01 completed successfully! Frankly this was something of a surprise: It tests most of the instructions and ways of moving data and they all just worked.

Also, the run time of about 3.75 minutes matches very well with the information in the diagnostic listing for a 1410 with the Accelerated logic feature.

So then, I ran it again, but with overlapped I/O and priority features turned on in the diagnostic. It ran fine for about a minute, but then failed during overlapped execution of a multiply instruction. More on this during the next installment.

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