Today's project, for which I spilt blood, is finally to get a log of the output from the garage mounted solar panels, using a 40 year old computer to do the logging just because, er, why not? An Arduino is calculating output in watts from the time between pulses which come from an energy meter in the garage, sending them by serial connection to the NEC PC8201a which does the logging.
It's powered by a very old and slightly crusty home made variable power supply.
The NEC is running a program written in Microsoft BASIC. Like most people of my age I started writing BASIC before this computer was made, but it's far from my favourite language so I've not written any BASIC in a very long time (except a loader for a spectrum program a few years ago). Because I had never used it before, and on this occasion I could, this program uses the ON COM GOSUB feature. This feature interrupts the flow of the main program whenever data arrives on the serial port, similar in concept to how hardware interrupts work on the processor itself. A bizarre thing for any BASIC dialect to include! As this is BASIC, all variables are global and there's no stack to save state on.