Spin Semiconductor

Ive been reading all the documentation in depth and I don't fully understand the PACC, it says on several of the instructions they copy the ACC to the PACC first, but on the block diagram in the user manual it says that PACC is the previous sample. Is this one or the other or both? like if those opcodes copy the value to the PACC, and something else accesses it, would it be the value just output from the prior opcode during this cycle?

am I crazy or don't you need the previous cycle sample rather than one which was stored this cycle by an opcode just before it to make reliable filter coefficients based on the sample rate? are there other implied uses for PACC?

I kindof get how this type of thing works with the LR register for chaining all pass delays, id love more info on that if there is any.

PACC is simply ACC from the last instruction, useful for things like a low-pass or high-pass shelf, see the WRLX and WRHX instructions.

so to get a zero cross detection does that mean I would read the adc in two subsequent instructions and skp zrc?

Yes, something like that should work

Does the SKP instruction affect PACC? Or is it only ACC-changing functions that affect PACC?

SKPs should not have any affect on PACC, only instructions that change ACC (and are not being skipped) should change PACC.