Debugging the ALU v 1.1

Posted on Wed 31 July 2024 in MUPS16

Notes:

  • low-temperature solder paste does not flow nearly as well as original version. Maybe because it's not thermally stable, and I'm not storing it at a constant temperature?

  • short between VCC and GND after assembly and soldering. Removed 48 of 60 capacitors before finding the culprit on the 49th.

  • bug in AND operations. e.g.

    ` AssertionError: 1001100100100011 & 0101101000001100 got 1111001100110011, expected 0001100000000000 `

  • tracked down to output of op_sub being low when alu_op is 0b0000, which should not be possible.

  • very inconsistent, except that it reliably fails in bit positions 2 and 7

  • weirdly, alu_out_en consistently has a voltage of 3.06 when it's meant to be low. No obvious shorts on the PCB.

  • moving tester card to a B slot 'fixed' all the problems, and all tests pass. Something dodgy with the A slot?

alu pcb