Big Mess o’ Wires

I showed off BMOW to an old college friend the other day. He and I did all the digitial electronics labs together at MIT, where I learned what little I know about how to build a computer. Sadly, he seemed to think I was a little insane for all the energy I’ve put into this project, but I have to admit my demo was a little underwhelming. It didn’t help that MSBASIC crashed when I tried to show it off.

Yes, the random crash bug with string manipulation came back. Again. I’d earlier thought it was 100% present with one version of the code, and 100% absent with another, but it started happening intermittently with the “good” version of the MSBASIC code. Six months ago I would have set up the logic analyzer again, and gone digging for the source of the bug, but I couldn’t bring myself to do it this time. My previous investigations had suggested that memory at $149F was getting overwritten or misread somehow, so I made a very quick and ugly “fix” to the MSBASIC code to avoid that location altogether. In fact, I relocated the whole program image to begin at $1500, wasting about 5K of RAM. That seems to have resolved the problem, but it’s a pretty ugly fix. This bug will almost certainly come back to bite me again later, under other circumstances and at a different memory location.