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An implementation of the ISO-TP (ISO15765-2) CAN protocol in C

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ISO-TP (ISO 15765-2) Support Library in C

This is a platform agnostic C library that implements the ISO 15765-2 (also known as ISO-TP) protocol, which runs over a CAN bus. Quoting Wikipedia:

ISO 15765-2, or ISO-TP, is an international standard for sending data packets over a CAN-Bus. The protocol allows for the transport of messages that exceed the eight byte maximum payload of CAN frames. ISO-TP segments longer messages into multiple frames, adding metadata that allows the interpretation of individual frames and reassembly into a complete message packet by the recipient. It can carry up to 4095 bytes of payload per message packet.

This library doesn't assume anything about the source of the ISO-TP messages or the underlying interface to CAN. It uses dependency injection to give you complete control.

The current version supports only single frame ISO-TP messages. This is fine for OBD-II diagnostic messages, for example, but this library needs some additional work before it can support sending larger messages.


First, create some shim functions to let this library use your lower level system:

// required, this must send a single CAN message with the given arbitration
// ID (i.e. the CAN message ID) and data. The size will never be more than 8
// bytes.
bool send_can(const uint32_t arbitration_id, const uint8_t* data,
        const uint8_t size) {

// optional, provide to receive debugging log messages void debug(const char* format, ...) { ... }

// not used in the current version bool set_timer(uint16_t time_ms, void (*callback)) { ... }

With your shims in place, create an IsoTpShims object to pass them around:

IsoTpShims shims = isotp_init_shims(debug, send_can, set_timer);


With your shims in hand, send an ISO-TP message:

// Optional: This is your callback that will be called when the message is
// completely sent. If it was single frame (the only type supported right
// now), this will be called immediately.
void message_sent(const IsoTpMessage* message, const bool success) {
    // You received the message! Do something with it.

IsoTpSendHandle handle = isotp_send(&shims, 0x100, NULL, 0, message_sent);

if(handle.completed) { if(!handle.success) { // something happened and it already failed - possibly we aren't able to // send CAN messages return; } else { // If the message fit in a single frame, it's already been sent // and you're done } } else { while(true) { // Continue to read from CAN, passing off each message to the handle // this will return true when the message is completely sent (which // may take more than one call if it was multi frame and we're waiting // on flow control responses from the receiver) bool complete = isotp_continue_send(&shims, &handle, 0x100, data, size);

    if(complete && handle.completed) {
        if(handle.success) {
            // All frames of the message have now been sent, following
            // whatever flow control feedback it got from the receiver
        } else {
            // the message was unable to be sent and we bailed - fatal
            // error!


Finally, receive an ISO-TP message:

// Optional: This is your callback for when a complete ISO-TP message is
// received at the arbitration ID you specify. The completed message is
// also returned by isotp_continue_receive, which can sometimes be more
// useful since you have more context.
void message_received(const IsoTpMessage* message) {

IsoTpReceiveHandle handle = isotp_receive(&shims, 0x100, message_received); if(!handle.success) { // something happened and it already failed - possibly we aren't able to // send CAN messages } else { while(true) { // Continue to read from CAN, passing off each message to the handle IsoTpMessage message = isotp_continue_receive(&shims, &handle, 0x100, data, size);

    if(message.completed && handle.completed) {
        if(handle.success) {
            // A message has been received successfully
        } else {
            // Fatal error - we weren't able to receive a message and
            // gave up trying. A message using flow control may have
            // timed out.



The library includes a test suite that uses the

C unit test library.
$ make test

You can also see the test coverage if you have

installed and the
environment variable set to your choice of web browsers:
$ BROWSER=google-chrome-stable make coverage



Copyright (c) 2013 Ford Motor Company

Licensed under the BSD license.

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