Module msg_queue

Expand description

FIFO queue with a packet-based interface preserving packet boundaries

The MsgQueue is implemented on top of the ByteQueue. It handles variable-sized messages using the following format:

Field	Size
Message Prefix	Fixed size, configurable
Protocol Version	1 byte
Data Size	4 bytes in little endian
Header CRC	4 bytes in little endian
Data	variable-sized - determined by the data size field
Message CRC	4 bytes in little endian

The Message Prefix is a fixed-size field provided by the user to identify the beginning of a new message. If it is guaranteed that the memory will not be written by other processes, it may also be left blank (b"") but a short prefix will also not hurt much and provide more robustness. Theoretically, the prefix could also be used to categorize messages, i.e. to multiplex different message channels over the same memory. But currently, this is not implemented and there are currently no plans to do so and a MsgQueue will consider all bytes preceding the prefix as garbage and remove them.
The Protocol Version is a 1 byte value specifying the version of the communication protocol being used for compatibility checks. It is set to a constant value for each protocol version and guarantees robustness between library versions with protocol changes.
The Data Size specifies the length of the message data.
The Header CRC checks the integrity of the Message Prefix, Protocol Version, and Data Size. This has been introduced to prevent getting stuck when the Data Size field contains garbage which is interpreted as huge message length so that the MsgQueue would wait forever. Since the library is no_std, this approach has been taken instead of a classic timeout.
The Data field contains the actual message data.
The Message CRC ensures the integrity of the entire message packet.

Structs§

MsgQueue: The MsgQueue queue type using ByteQueue as the underlying communication mechanism. Read the crate and module documentation for further information and usage examples.