stapelzeiger / serial-datagram

send datagrams over a serial interface (byte stream)

Serial Datagram

Send datagrams over a serial link (byte stream).

Key features:

• Detect transmission errors (using CRC-32)
• "Hot-pluggable": automatically synchronizes with the data-stream by detecting the start of a new frame
• Low overhead
• No dynamic memory allocation

Protocol

A datagram frame looks like this:

[data][CRC32][END]

The CRC32 is the "Ethernet" CRC32 (polynomial 0x104C11DB7, inverted, initialized to 0) checksum of the (unescaped) data bytes transmitted MSByte first (big-endian).

The data and CRC32 fields are escaped such that an END byte is replaced by [ESC ESC_END] and an ESC byte is replaced by [ESC ESC_ESC].

Hex value	Abbreviation	Description
0xC0	END	Datagram End
0xDB	ESC	Escape
0xDC	ESC_END	Transposed End
0xDD	ESC_ESC	Transposed Escape

serial-datagram's Issues

call send function with length 0

I suggest not calling the send function in serial_datagram_send if the buffer length is zero.

for example here insert:

if (b - a > 0) {
    send_fn(sendarg, &dtgrm_byte[a], b - a);
}

Change signature of send callback

Currently the signature of the send callback is :

void (*send_fn)(void *arg, const void *p, size_t len);

Since the length is given in bytes, it would make more sense to give p such that sizeeof(*p) == 1. I suggest changing the type to :

void (*send_fn)(void *arg, const uint8_t *p, size_t len);

This is by no mean an emergency, but I think it would be neater.