Slow I2C bus

I've got a couple of I2C devices that I want to drive from the
BeagleBoard, but they can only cope with I2C at 100kHZ. I could change
the speed of i2c-2 by tweaking the kernel, but

1) It's a lot of work for a small change
2) I have other stuff I want to run at 400 kHz.

Is it safe to use the SDA/SCL on the LCD header, as that appears to
run at 100kHz? And if so, are they level-shifted? I've seen at least
one post here that says they are, but the xM manual says they are 1.8
v.

Romilly

I've got a couple of I2C devices that I want to drive from the
BeagleBoard, but they can only cope with I2C at 100kHZ. I could change
the speed of i2c-2 by tweaking the kernel, but

1) It's a lot of work for a small change
2) I have other stuff I want to run at 400 kHz.

Same problem here. I tweak the kernel. Works for me. What I really would
like to have however would be a way to switch the I�C speed on the fly
using a user-space API. (this is possible for SPI btw..).

Is it safe to use the SDA/SCL on the LCD header, as that appears to
run at 100kHz? And if so, are they level-shifted? I've seen at least
one post here that says they are, but the xM manual says they are 1.8
v.

I can only comment for the BeagleBoard Classic (not XM). On this system
the SDA/SCL of the LCD header are level-shifted and run at 100Khz. The
are however connected to the hdmi output, so if you plug in a monitor
you will see the monitor on the I�C-bus. That may or may not be a
problem for your application.

For the Beagleboard XM you should take a look at the schematic and see
if a level-shifter is there and at what voltage it shifts. You can also
measure the voltage between ground and SDA or SCL for a quick check. The
voltage on these lines will float up to the shifted voltage if no I�C
transaction is in progress.

Cheers,
  Nils

Thanks, Nils.

I'm used to looking up the source for Open Source Software. I forgot I
could do that for OS hardware as well!

Cheers, Romilly