Re: [RFC] K-Line protocol via SocketCAN

[Patrick Menschel <menschel.p@posteo.de>]

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>> I remember a K-Line implementation for Linux where we had a MPC5200 UART
>> which we programmed with bit-banging of some control line to do the
>> 5bit/s opening pattern.
>> After that we went to 10400 bit/s and did some K-Line communication.
>> All this was done by a user space application on /dev/ttyS0.
> 
> Yes, and this does make perfect sense until you start dealing with
> faster modes and need more precise timing. The K-Line is limited by
> 250kBaud/s bus speed.
> 

Hello Marek,

Afaik there is no ECU left that actually needs the "5 Baud INIT".
Most ECUs use the "FAST INIT" procedure, means 25ms low, 25ms high, then
start communication with 10400Baud.

The nasty part are the 25ms low, 25ms high , that is also prior to the 5
Baud Init pattern.

After that, everything on the K-Line is pure serial communication.

I've done a few test myself with an FT232RL based KKL-Interface and
these 25ms low, 25ms high are very hard to realize. No Success at my end.

From my point of view, the 25ms low, 25ms high are the only reason to
move into kernel space and possibly switch the Tx Pin to GPIO and pull
it low/high for 25ms, then switch it back to UART.

Regards,
Patrick



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