Post #2474894
2026-04-17 12:00 UTC
@nedbat@hachyderm.io Once Upon A Time to see how computers really worked you could code in assembler and watch the results on a logic analyser and/or oscilloscope.
But that went out of the window decades ago. The rot started to set in when CPUs were no longer in DIL 0.1" packages, progressed with the invention of on-chip caches (so that not every memory fetch was a visible bus cycle), and has got vastly worse since (with CPUs no longer executing the instructions you wrote, either in the order you wrote them or, sometimes, at all).
Replies (2)
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@TimWardCam@c.im 2026-04-17 12:03
@nedbat@hachyderm.io "Oscilloscope? Really?" Yes really. Once I had trouble with the first dozen or so bootstrap instructions on a system - it didn't get to the point where all the built-in debugging features could start working. So we hooked up an oscillator to continually poke the CPU's RESET line, and read off each address and data line one at a time with a scope, to see what the first few instructions were doing. Yes this was slightly tedious, but it got us to diagnose and fix the bug (I don't recall whether it was hardware or software - this was prototype hardware as well of course).
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@nedbat@hachyderm.io 2026-04-17 13:57
@TimWardCam@c.im the rot? I'm sorry that computers are fast now.