isotp-c/README.mkd

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.

## Usage

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.
    void send_can(const uint16_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
    void set_timer(uint16_t time_ms, void (*callback)) {
        ...
    }

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

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

### API

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

    // Optiona: 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.
                }
            }
        }
    }

## Testing

The library includes a test suite that uses the `check` C unit test library.

    $ make test

You can also see the test coverage if you have `lcov` installed and the
`BROWSER` environment variable set to your choice of web browsers:

    $ BROWSER=google-chrome-stable make coverage

## Authors

Chris Peplin cpeplin@ford.com

## License

Copyright (c) 2013 Ford Motor Company

Licensed under the BSD license.