OBD-II Support Library in C
=============================

TODO isotp needs to accept responses on an ID other that the request's arb id -
or maybe we have 2 isotp instances, for rx and tx.

* Response's arb id is assigned ID plus 0x8
* Functional daignostic request (Broadcast), 0x7df arb id
* Standard ECU requests to 0x7e0 - 0x7e7

* Some requests don't need PIDs - e.g. mode 3
    * some responses don't have PIDs, just payload - e.g. mode 3

* Service ID + 0x40 == positive response
* Response includes PID echo - use this to match up request/response
* Response ID, ISO-TP PCI, ISO-TP length, service response ID, PID echo, data

I send the request and give a callback
when the response arrives for the matchin service and PID - on any arb id, since
this may be a broadcast - call my callback.


TODO do you want to provide the callback to the Handler, or to each
individual send?o
ok, what are the use cases here.

you're going to request a few PIDs over and over again at some frequency
you're going to request DTCs once and read the response
you're going to clear DTCs once

i'd rather use the same diagnostic handler to send all of the differet messages
rather than create one for each use. that way ai can

but that does complicate the memory management because it'll need to create
some internal data structures.

at the simplest, what does this handler have to do?

* store the request arb id, mode, pid, and payload locally
* send a can message
* get all new can messages passed to it
* Check the incoming can message to see if it matches one of the standard ECU
  response IDs, or our arb ID + 0x8
* if it matches, parse the diagnostic response and call the callback

that seems pretty simple and not worth greatly increasing the internal state to
handle multiple requests

what we need is another layer on top of that to handle the repeated requests.

## API

    void my_callback(const DiagnosticResponse* response) {
    }

    DiagnosticRequestHandle handle = diagnostic_init(my_callback);
    DiagnosticRequest request = {
        arbitratin_id: 0x7df,
        mode: OBD2_MODE_POWERTRAIN_DIAGNOSTIC_REQUEST,
        pid: 3
    };

    diagnostic_send(&handle, &request);
    while(true) {
        diagnostic_handle_can_frame(&handle, 42, data, 8);
    }

    diagnostic_request_pid(&handle, DIAGNOSTIC_STANDARD_PID, 42

    diagnostic_destroy(&handle);

## Testing

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

    $ make test

## Authors

Chris Peplin cpeplin@ford.com

## License

Copyright (c) 2013 Ford Motor Company

Licensed under the BSD license.