Small improvements in system lib
Improved return statement of sensors app
Add DMA error handling.
Add serial error handling.
Add short-packet-reception handling (this may allow us to send/receive shorter packets… needs testing).
Add PX4IOv2 support to the uploader.
Fix printing of PC_COUNT perf counters
iov2 pin definition cleanup sweep
Switch to the 'normal' way of doing register accessors.
Be more aggressive en/disabling DMA in the UART, since ST say you should.
More test work on the px4io side of the serial interface.
One more piece of paranoia when resetting DMA
Reset the PX4IO rx DMA if we haven't seen any traffic in a while; this gets us back into sync.
Improved limits handling
Fixed HIL handling
Added gyro scaling as parameter
Commented flow example slightly better
Use the NuttX built-in crc32, it works fine.
Always send and expect a reply for every message.
Encode the packet type and result in the unused high bits of the word count.
Add an 8-bit CRC to each transmitted packet.
Check packet CRCs and count errors; don't reject packets yet.
Eliminate the TD DMA callback; we don't need to know that it's completed.

Fix abort behaviour on timeouts, now we don't wedge after the first one.