Labor-Octet-Protocol/en

Throughout this document a byte is considered an bit-octed, a dataword of 8 bit length.

About

The Labor-Octet-Protocol (LOP) allows you to communicate in a message and stream oriented way.

The protocol builds upon a deeper communication layer which is able to transmit bytes.

Structure

Escape-Layer

In order to allow (atomic) commands it is necessary to assign some byte values special meaning. In order to allow this values also appear in normal dataflow we use a technique called escaping.

command byte	meaning
0x42	reset
0x23	escape

escape-sequences	payload data
0x23 0x01	0x42
0x23 0x02	0x23
0x23 0x03	0x11
0x23 0x04	0x13

The two additional escape sequences allow usage of regular software flowcontrol (XON/XOFF) which is often used.

commands

0x23 0x14 message

The sequence 0x23 0x14 starts a new message. The following two bytes represent the length of the message (not including 0x23 0x14 and the length bytes). The length is encoded in big endian, which means that the first byte is the most significant. The messages follows the two length bytes.

0x23 0x15 stream sync

The sequence 0x23 0x15 is a special marker in the data stream which is useful for synchronization.

Implementation

AVR-Microcontroller

An implementation of LOP is available for AVR-microcontrollers [1].

LOP-Kontext

typedef struct lop_ctx {
	lopstates_t rxstate, txstate, msgretstate;
	uint32_t msgidx;
	uint16_t msglength;
	uint8_t* msgbuffer;
	uint8_t escaped;
	void (*sendrawbyte)(uint8_t);           /* pointer to the writing function */
	void (*on_msgrx)(uint16_t, uint8_t*);   /* function called on message recieve */
	void (*on_streamrx)(uint8_t);           /* function called on recieve of a stream byte*/
	void (*on_streamsync)(void);            /* function called on recieve of streamsync */
} lop_ctx_t;