Add Error Capture Logic to uC

[ChrisPVille]

Every once in a while the drive asserts a non-resettable fault after sitting idle, post-spindown, for a while. It seems to spontaneously disappear before I go to probe it. It might be an electrical margin issue.

Write some code and modify the FPGA to interrupt the microcontroller so it can capture the error condition the instant it happens, before it goes away. This type of error handing will be required for robustness anyway.

[ChrisPVille]

Quickly poking around, it looks like spin error gets asserted by the drive. This is probably an issue with the actual drive logic board, as spin error isn't supposed to assert on spin-down (because that would be dumb).