3 ms·
This was on occasional occurrence on Acorn's BBC Micro, which was 6502-based and had a 16-bit free-running timer. There were a number of then-little-known detai
by to3m 12y ago
This was on occasional occurrence on Acorn's BBC Micro, which was 6502-based and had a 16-bit free-running timer. There were a number of then-little-known details of the 6502's operation and the interaction between the 1MHz timer clock and the 2MHz CPU clock that made it difficult to predict what the hell was going on (on top of the usual code obfuscation tricks).
Interesting thread - well, for former BBC Micro programmers perhaps! - on the topic: http://stardot.org.uk/forums/viewtopic.php?f=1&t=696 http://stardot.org.uk/forums/viewtopic.php?f=1&t=696
- makomk 12y agoThat is an interesting copy protection scheme, partly because it'd probably be a criminal offence to write anything like it these days. It contains code intended to silently reformat whatever's in the floppy drive if any of the checksums fail - something that could easily happen if the tape or hardware's even slightly flaky - and because genuine copies are loaded from tape that's going to be an unrelated floppy, quite possibly one with important data on it.