MegaCAN

Library for interacting with Megasquirt CAN Protocol on Arduino-compatible hardware (Arduino, Teensy, Feather, etc.). Hopefully this makes it relatively easy to:

• Receive and store 11-bit advanced broadcast data from Megasquirt. ** Simple dash broadcasting not currently supported, will be added later.
• Receive and interpret 29-bit (extended) requests for data from a Megasquirt.
• Prepare a response to the Megasquirt's request for data.

Installation and Adding to a Sketch

Simply download a zip of this respository, add a "MegaCAN" directory to your Arduino/Libraries director and extract the zip contents there.

Usage

Including in your Arduino sketch

To use the library in a sketch, add the following to your Arduino sketch: #include <MegaCAN.h>

Limitations of the library

Note that this library does not actually handle CAN communications! However, it should be compatible with most CAN communication libraries. It has been tested primarily with FlexCAN_T4, but also on a limited basis with SparkFun's CAN-Bus library. If your library can separate out an 11-bit CAN ID and the corresponding data buffer in a CAN message, the CAN broadcasting function will work. If the library can handle extended 29-bit CAN IDs, flags, and data buffer in both read and write, then you'll be able to send data back to Megasquirt!

Using the library's structures and functions

Although you can access all structures/objects, classes, functions, etc. from your Arduino sketch, unless you have a reason, you probably only ever need to interact with the following:

• MegaCAN_message_t: a structure that stores the parameters of 29-bit proprietary Megasquirt CAN protocol.
  • This is only needed if you're looking to send data to your Megasquirt's GPIO ADCs.
  • Currently, you'll want to create one of these for requests from Megasquirt and another for responses to Megasquirt.
  • You shouldn't need to interact directly with all of the objects in a MegaCAN_message_t, but you might need the following:
    • If you intend to use more than one of the sets of GPIO ADCs, you'll need to check which one MS is asking about: this is in the core.toOffset object within the request MegaCAN_message_t, and corresponds to the "offset" setting in the "CAN bus/Testmodes > CAN Parameters" dialog in TunerStudio.
• MegaCAN_broadcast_message_t: a structure that stores any and all of the parameters that Megasquirt can send with its "Advanced Real-time Data Broadcast". Currently, simple dash broadcasting is not supported, but will be added in the future.
  • To access the data, if for example you store the broadcast data in a MegaCAN_broadcast_message_t called bCastMsg, you get the data by simply calling bCastMsg.<dataName>, where <dataName> corresponds to the names in the 2016-02-17 version of the Megasquirt CAN Broadcasting Manual Advanced Broadcasting Field List. I.e. if you want engine speed, simply call bCastMsg.rpm.
• MegaCAN: a class with the few functions needed for all of this to work:
  • MegaCAN(): The constructor for this class requires the following argument:
    • baseID: A constant uint32 that matches the base CAN identifier value in your megasquirt settings
  • processMSreq(): Processes a 29-bit extended CAN message received from Megasquirt, requiring the following arguments:
    • msgCore: A uint32_t that contains the ID parameter of the request message, which Megasquirt encodes with:
      • The table on the remote device that Megasquirt is requesting data from (see TunerStudio settings)
      • The offset within that table where Megasquirt is requesting data from (see TunerStudio settings)
      • The message type (this library currently only supports requests and responses)
      • The "From ID", i.e. the Megasquirt's CAN address/ID
      • The "To ID", i.e. the address/ID Megasquirt is looking to receive data from
    • msgData[3]: The three uint8_t bytes of the request message's data buffer, which Megasquirt encodes with:
      • The table in the Megasquirt where the response data from the remote device will be stored.
      • The offset within that table where Megasquirt will store the response data
      • The number of bytes of data Megasquirt is requesting
    • &msg: A MegaCAN_message_t where the above request message parameters will be stored.
  • setMSresp(): Encodes the response to a Megasquirt CAN data request into a CAN ID and data buffer, requiring the following arguments:
    • recMsg: The MegaCAN_message_t where the request message parameters were stored by processMSreq().
    • &respMsg: A MegaCAN_message_t where the response message parameters will be stored.
    • var0, var1, var2, var3: uint16_t encoded data variables; the actual data that you want to send to each of the four GPIO ADC channels in the Megasquirt.
  • getBCastData(): Processes an 11-bit Megasquirt Advanced Data Broadcast CAN message into the values shown in the Megasquirt CAN broadcasting manual.
    • You'll need to call this function every time you get a CAN broadcast message from Megasquirt if you don't want to miss data!
    • This function uses the baseID value you passed into the constructor.
    • Requires the following arguments:
      • id: The uint32_t CAN message ID parameter of the received broadcast message.
      • data[8]: The eight uint8_t bytes of CAN message data buffer of the received broadcast message.
      • &msg: The MegaCAN_broadcast_message_t where you want to store the processed data.
• Temperature unit conversion:
  • Add "#define CELSIUS" to the precompiler code in your Arduino sketch to automatically convert any temperature-unit broadcast data from the Megasquirt to celsius; if you don't include that in your code, the default of Fahrenheit will be used.
  • This is implemented in the getBCastData() function, and will happen automatically any time you process a broadcast message received from the Megasquirt.

Disclaimer, Issues, Contributing, Requests

I am using it on my own car to simultaneously process broadcast messages, and send data back to a Megasquirt 2 with the Extra 3.4.3 firmware using the 29-bit extended request/response protocol for datalogging extra channels. With roughly 1000 miles of driving, it has worked flawlessly. That said, I am by no means a professional developer, and since this is my first library, I am sure there is room for improvement. I'll do my best to help if you encounter problems, and if you have suggestions for improvement, bug fixes, feature requests, by all means let me know what should be changed!

To Do

• Include examples.
• Add simple dash broadcasting support.
• Add a config file to make it easier to turn features on/off to save memory and improve usability.