I2C Bus Sniffing

[devnull]

Has anybody done anything on this that could help me from reinventing the wheel ??

I can do this with bus-pirate but I would like to be able to do it with uPython.

I guess the only way would be bit-banging using an interrupt pin ?

[deshipu]

What are you trying to do exactly?

[devnull]

Listen to a battery talking to it's parent device.

[deshipu]

To collect raw clocked data, you can use the SPI peripheral, but you will still need to find some way to get the start and stop conditions somehow — probably with a pin interrupt, as you wrote. There is one more problem — you won't know which of the devices is pulling the line at any given moment — for that, your board would have to act as a man-in-the-middle, having each device connected to a separate set of pins and repeating what they do to the other device.

[dhylands]

Using the SPI interface will only work if a device doesn't stretch the clock.

You probably want to create a new I2C-sniffer module based on the software I2C code, or add a mode to the software I2C module to allow it to be a sniffer.

To be a sniffer the SDA and SCL signals will always be inputs and would never be driven.

[deshipu]

Why won't SPI work with clock stretching? The clock line will remain low until the new bit is sent, whether it's stretched or not, so I think it should work?

[dhylands]

You're right. I wasn't thinking about this in the right context. I think that the issue would be detecting start & stop bits and dealing with the ack/nack.

[devnull]

Thanks but writing a module is beyond my capabilities, I was hoping to be able to do this within Python.