sniffer: UART format is too verbose

[jnohlgard]

Sometimes when receiving many frames in a short period of time, the UART speed is too low to be able to capture every frame. The current format of the sniffer output is very verbose and the data is hex encoded in ascii, so every sniffed byte will use three bytes on the UART.
Changing the format of the UART output into something like SLIP encapsulated 802.15.4 frames would significantly reduce the risk of lost frames.

This is an example output from the current version of the sniffer, the frame contains a 6lowpan compressed ICMPv6 echo request packet with the destination address ff02::1

rftest-rx --- len 0000001F lqi 79 rx_time 00000000025A4D96
41 D8 D0 23 00 FF FF 4E 6E B7 36 29 53 14 23 7A 3B 3A 01 80 00 C1 F4 00 53 00 03 53 53 53 53

The LQI and RX timestamp could be appended/prepended to the frame data to preserve the same functionality.

This change would possibly affect the shell functionality in the sniffer, the terminal program on the PC side might not handle raw binary data well, so the sniffer would need to be used together with the sniffer script to handle demuxing the binary frames from the shell text.

[miri64]

Mh... That could be a motivation to finally make shell multiplexing over slip possible :-) (which is on my todo list basically ever since SLIP was reintroduced for netdev, as it was possible with my B.Sc. thesis implementation of SLIP).

[miri64]

Another oportunity could be to utilize usbdev (RIOT-OS/RIOT#9830) so that the RIOT device is recognized by Wireshark as a network interface directly. I've seen this done with a Contiki-based sniffer @kaibeckmann showed me.