SPI:
- use PDC DMA for SPI transfers
- use real SPI clock divisor (4.8MHz) rather than current 320kHz clock

RC632:
- Fix locking between 'atomic' ops like set/clear bit and RC632 IRQ
- Implement VFIFO handling

USB:
- don't busy-wait for EP2/EP3 transfers but rather use TX completion IRQ
- Implement VFIFO handling
- Add DFU descriptor to host

DFU:
- implement DFU protocol for memory and flash
- add capability to copy and execute DFU from RAM

Generic:
-

Later, for PICCsim:
- Implement SSC code for sampling subcarrier
- Implement SSC code for generating subcarrier
- Implement Manchester coding

Way Later, for librfid:
- Implement parts (or all of) 14443 in firmware as alternative configuration
