MS3 board USB to UART converter/CAN Passthrough

[thomas505]

Hello again,
Hopefully this should be an easy one this time . I'm finishing up the firmware for an MS3 dash display that i've been working on (to complement my MS3 card - which is another topic). And a few things have cropped up that I wouldn't mind changing, one of these being the ability to use CAN passthrough to tune the MS3 remotely. Now i've pretty much got my head around the CAN side of things, and the documentation for the serial protocol definately seems detailed enough but I still need to actually hook a laptop up to my PIC18F4580 (which has a hardware USART port - just like about every PIC i've ever seen ) and would rather use USB than a serial port (as my laptop doesn't have a serial port ).

Now, my question , what is the chip that the MS3 uses as a USB - serial converter? I am 99% sure its from FTDI and I *think* its an FT232 or something along those lines? If anyone can help me out it would be greatly appreciated.

Thanks again, Thomas.

EDIT: Looks like an FTDI FT232R will do what I want? (Although I definitely wouldn't mind the EXACT same chip )

[WestfieldMX5]

Definitely a FTDI FT232R, drivers here.

[thomas505]

Awesome, thanks for the prompt reply.

[thomas505]

Next question,
In the CAN technical documentation, it mentions the following:

Older code versions were limited to only sending or receiving data in 8 byte blocks and required the specification of a “blockingFactor” However, this limit has been removed as the Megasquirt-3 (and MS2/Extra) codes automatically buffer the requests so the tuning software may send or request larger blocks of data. Without this automatic buffering the overhead of the serial commands was large and transfer rates were very low. So the tuning software MUST know if this is a local or remote request and if it is dealing with an older firmware it must only ask or send a maximum of eight data bytes at one time for the remote transfers.

Now, how large is this buffer? I think I remember reading 1000 bytes somewhere? But I can't seem to find it again... Also, does the MS3 make use of the hardware handshaking/FIFO buffer in the FT232RL at all? Or does it simply accept all data and return buffer full if the buffer has overrun (this is what I think is the case).

Any help appreciated.

[jsmcortina]

MS3 handles the FT232 just the same as the MAX232. The CPU serial module TX and RX (ONLY) are connected.

James

[thomas505]

Awesome, from here the only thing I need is buffer information. Was I correct in saying the MS3 uses a 1024 byte buffer for serial? And if so, is it possible to use a smaller buffer (preferably 256 bytes, though I could do 512) or will tunerstudio keep trying to send 1024 byte messages?

Thanks, Thomas.

[jsmcortina]

I need more context to understand your question. It sounds like it more for Phil to answer though. The MS3 (1.1) can handle packets of up to 1k.

James

[racingmini_mtl]

If I understand what you want to do correctly, the buffer size is not critical. Even if TS sends a 1024-byte packet, since the CAN bus speed is much higher than the serial port speed you shouldn't need to buffer much more than one CAN packet (8 bytes). I don't think you want to buffer the complete packet and then send it over CAN because that will slow down communications a lot.

Jean

[thomas505]

I need more context to understand your question. It sounds like it more for Phil to answer though. The MS3 (1.1) can handle packets of up to 1k.

James

I want to implement CAN passthrough for the new serial format (as everything else so far seems to be working fine).

If I understand what you want to do correctly, the buffer size is not critical. Even if TS sends a 1024-byte packet, since the CAN bus speed is much higher than the serial port speed you shouldn't need to buffer much more than one CAN packet (8 bytes). I don't think you want to buffer the complete packet and then send it over CAN because that will slow down communications a lot.

Jean

But then how would you check CRC? From my understanding you require the entire packet to be stored to verify its contents.

[racingmini_mtl]

In CAN passthrough, any CRC verification should be done by either the PC or the MS3 not the passthrough device. But that's my opinion and I don't know if that works with the current implementation of TS or MS3. James and Phil will have to chime in. If that's not the case then it's a problem because the communications are being slowed down uselessly. And there is also the need to buffer every packet in full.

I should add that the CAN protocol is reliable so a CRC check is not needed for that part of the comm link.

Jean