RomRaider

Hi guys,

I'm currently playing with the concept of reading in SSM2 via CAN using a microcontroller. I have an MCP2515 working with some demo arduino code, reading on standard OBDII stuff.

The MCP2515 seems to have only 8 bytes of data buffer per message - which appears to be a problem, as some of the messages in SSM2 via CAN are greater than 8 bytes long. For instance, the ECU init process is huge.

I've looked at other CAN controllers, such as the AVR-CAN series of microcontrollers, they too seem to only support 8 bytes.

Am I interpreting the data-sheets in correctly, or am I right in my understanding that these 8-byte controllers are not sufficient for SSM ?

Thanks,

Adrian

You will need to double buffer on the receive side. Your code should read the 8 byte CAN message, extract the payload and then buffer it some where appending the remaining parts of the message until it's complete. The SSM protocol will tell you how many bytes to expect after the header has been detected.

okay..

so i'm a little confused. i've done some more reading since my original post, and read all about iso-tp/iso15765-2 being required for segmentation across multiple can messages.

Do I effectively need to code my own iso-tp "middleware" that sits in between my SSM send/receive routines, and the lower layer MCP2515 driver ?

Or does the SSM protocol sit directly above the CAN physical/data-link layer protocols ?

SSM -> ISO15765-2 -> CAN.
Here's a bit of info you can digest:
http://subdiesel.wordpress.com/generic/ ... 2-via-can/

Yes - you do need to implement the iso15765-2 protocol (multi frame messages). SSM2 or OBD-II sits on top.

Are you using the arduino can bus shield ? The example code that comes with that basically implements the simple single frame case of iso15765-2. Extending it to handle the multi frame case is a bit of work, but not too hard.

I have done this using the MPC2515 (can bus shield) on an arduino and it works perfectly - used http://en.wikipedia.org/wiki/ISO_15765-2 as a reference.

care to share your source code?

PM me if you want the code..

Its a hacked version of the canbus shield code, its not really in a state where I want to "release" it as I got seriously side tracked and have not worked on that project for a few months, but happy to share.