What Happens When a CPU Starts

Re:What Happens When a CPU Starts by snvzz on Wednesday January 11, 2023 @05:03AM (#34336854)

Similarly, I have come to appreciate rehsd's[0] efforts in building a 80286 computer.

0. https://www.youtube.com/@rehsd/videos

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Re:What Happens When a CPU Starts by rep_lodsb on Wednesday January 11, 2023 @11:21AM (#34340163)

Wow, that series looks fascinating!

Only watched the first video yet, after initializing itself the CPU actually runs this code (because D8-D15 is wired to zero):

  addr    opcode
  FFFFF0  90           NOP
  FFFFF1  00 90 00 90  ADD [BX+SI+9000],DL
  FFFFF5  00 90 00 90  ADD [BX+SI+9000],DL
  FFFFF9  00 90 00 90  ADD [BX+SI+9000],DL
  FFFFFD  00 90 00 --  !! general protection fault

You can see it read and write the same address three times, then fetch the interrupt 0Dh vector and push flags+CS+IP to the stack :)

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