TinyFrame

TinyFrame is a simple library for building and parsing frames (packets) to be sent over a serial interface (like UART). It's implemented to be compatible with C89 and platform agnostic.

Frames are protected by a checksum and contain a "unique" ID, which can be used for chaining messages. Each peer uses a different value for the first bit of all IDs it generates (the "master flag" or "peer_bit") to ensure there are no clashes. Typically the master (PC, main microcontroller) will use "1" and the surrogate (WiFi module, USB-serial connected gadget, display driver...) uses "0".

The library lets you bind listeners waiting for any frame, or a particular ID. This allows for easy implementation of async communication.

Frame structure

The frame makeup is inspired by that of SBMP (my other, more complicated and advanced UART protocol library).

<SOF><ID><NOB><PAYLOAD><CKSUM>

SOF ... start of frame, 0x01
ID  ... (master_flag | 7-bit counter) - the frame ID
NOB ... nr of payload bytes in the frame (1..256)
PAYLOAD ... NOB bytes of data, can contain any byte values 1..256
CKSUM ... checksum, implemented as XOR of all preceding bytes in the message

The frame ID (in SBMP called "session ID") can be used to chain multiple related messages and maintain the context this way. For example, a response may copy the frame ID of the request frame, which then triggers a callback bound by the requesting peer. Such behavior is application specific and is thus left to the upper layers of the protocol.

Usage hints

• Both sides of the protocol (slave and master) should include the same TinyFrame code.

• Master inits the lib with TF_Init(1);, while slave uses TF_Init(0);. This is to avoid a message ID conflict.

• Both sides can add Generic and Type listeners (callbacks) using TF_AddGenericListener(func) and TF_AddTypeListener(type, func). The listener is a function as showin in the example file test.c or declared in TinyFrame.h

  bool myListener(unsigned int frame_id, const unsigned char *buff, unsigned int len) { ... }

  The listener returns true if the message was consumed. If it returns false, it can be handled by some other listener (possibly a Generic Listener, if you added one)

• A message is sent using TF_Send(), and to use it, the TF_WriteImpl() stub must be implemented in the application code. See test.c for an example.

  There are also helper functions TF_Send1() and TF_Send2() which send one or two bytes.

• To reply, use TF_Respond() with ID same as in the received message (the listener gets this as it's argument). A listener provided as the last parameter to TF_Send() will be called after receiving the response.

• To remove a listener, use TF_RemoveListener(). Always remove your ID listeners after handling the response! There's a limit to the number of listeners.

• The function TF_Accept() is used to handle received chars. Call this in your UART Rx interrupt handler or a similar place.