snooping an external 400kHz+ i2cbus

Karin Willers karin at
Wed Sep 17 06:30:57 UTC 2008


you can have a look at the Beagle I2C/SPI/MDIO Protocol Analyzer at

Although I never used that thingie myself, I would consider buying it
when the need arises.

Greetings,  Karin
On Wed, 2008-09-17 at 03:06 +1000, Ian Smith wrote:
> Hi,
> Maybe off topic here, being about using i386 laptop/s to both monitor 
> and configure custom embedded devices that are programmed in assembler, 
> but if anyone can help with this, I figure they're most likely here ..
> An engineer friend and I have designed a little system that has one AVR 
> Tiny processor on either side of an electrically-isolated board, 
> communicating over an optically-isolated i2c-(hardware)compatible bus.
> The bulk of the traffic is small packets of feedback data about once per 
> ms.  Eventually using some multiplexing of i2c addressing to encode some 
> commands for compressed packets, but that's later; happy to run regular 
> I2C protocol during development and tuning.
> What we need is a device that can a) snoop and log bus traffic, from one 
> or the other side of the board, b) run in master mode for configuring 
> and dumping the AVRs while debugging and c) run in slave mode for 
> periodic data acquisition and monitoring, at 400Khz bursts at least.
> I dived into looking at iicbus system and drivers a couple of years ago, 
> thinking there must be a way to use lpbb at 400kHz, but the only master 
> and slave implementation found was then pcf for isabus at only 100kHz. I 
> know nowhere near enough about FreeBSD drivers (or even C) to write one, 
> though I may be able to hack on some existing code, with guidance.
> Are there perhaps now any pccard/cardbus or maybe USB adaptors that can 
> talk 400kHz or better I2C, that could conceivably be used for this job?  
> And more to the point, has anyone got it/them to work with FreeBSD?
> I'd be thankful for any pointers, or crumbs ..
> cheers, Ian
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