Wrapper is neccesary for the address offset and also because the
controller will trigger on reads/writes to registers, but we need access
to each byte of the 32 bit registers.
The wrapper will need to somehow chose when to actually trigger the
controller, maybe by having shadow registers?
1. in SD mode, CMD0 does not have a response, so we specifically ignore
it.
2. The penable signal was messed up, although it looks like this doesn't
matter anyway
3. The SD clock should be out of phase from the data signal by 180
degrees, so that we get max hold time
