System/1 Build Log

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An ongoing chronology of System/1's construction, and any other related musings.

20th June, 2014 (2) - Initial register file testing

This entry was backdated.

With the register boards and ICs neatly (or, in some cases, bodgily) fitted to the register file board, it's time to test it out with the help of some simple test routines running on the mbed.

The first few tests went well — storing and recalling values in the first two registers and the program counters — but after expanding the tests to the full sixteen registers weird problems started creeping in. The first was easily solved, as a closer inspection of a solder joint revealed a minute bridge to a neighbouring pin (which caused writes to one particular register to always update its neighbour at the same time), but I was still seeing strange glitches on some of the other registers. Most frequently, writing to register 3 would sometimes update register 12 at the same time, although not always and never (that I could tell!) vice versa.

Close inspection and thorough testing of connections has satisfied me that I'm not missing another short anywhere, but since I haven't managed to catch it in the act I can't figure out how else it might be misbehaving. Most vexing!

Somewhat dispiriting to hit a hurdle this early on in the project, but as I'm out of ideas for this evening I guess I'll just have to mull it over and try to coax the thing into working another time...