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Yeah, I agree. Often prohibitions are made without any context as to why they exist. I remember back in the 80s when I was a young kid (maybe 8 or 9) and I'd just started learning Z80 machine code. The manual for the computer had a strongly worded "do not use the alternate register set" (probably bolded and all caps), and sure enough the one time I tried, the computer crashed. I decided that it must be dangerous, and never tried that again. It was only years later when I discovered that the OS firmware used the alternate registers in the interrupt routines, and assumed that they were always set a certain way (in particular, BC was used to ensure ROM was visible not RAM before jumping into it, and on return RAM was paged back based on the existing contents of that register). So, if the warning had said "don't use the alternate register set unless you disable interrupts and save/restore the registers before re-enabling them", it'd have indicated what the problem was and why. Additionally, I think somewhere else there was a dire warning about "disabling interrupts for too long" with no indication what was too long or what problems it might cause. In reality the only thing it affected was the built in system clock which was only used by BASIC and the sound firmware, so for almost everything you might want to do it didn't matter in the slightest. (Actually, there was a slight caveat with the hardware that you actually did need to acknowledge the vertical sync interrupt within a certain time frame or it would fire at the wrong time on the next frame, but even if you did that, it would correct itself by the second frame, so again was entirely unimportant, especially if you never planned to return to BASIC). As well as not explaining the why, which helps understanding of the system generally, a list of prohibitions makes experimenting with the computer seem scary. One of the best things about old 8-bit home computers was that there was very little you could accidentally do in software that'd actually cause any lasting damage, unless you were deliberately doing stuff like toggling relays as fast as possible or fiddling with the monitor sync signals, sending excessively out-of-range timings and then left the monitor for a long time. |