Got i2c working ? Can you answer this ?

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    I'm trying to get an i2c interface going, and I'm not quite sure
where my problems lie. Suffice to say, it doesn't work.

    I have built an Philips style adaptor. The software modules appear
to load OK, and I have this in /proc

# ls -l /proc/bus
-r--r--r--    1 root     root            0 Jun 29 18:18 i2c
-r--r--r--    1 root     root            0 Jun 29 18:18 i2c-0
dr-xr-xr-x    3 root     root            0 Jun 29 18:18 isapnp
# cat /proc/bus/i2c
i2c-0   i2c             Philips Parallel port adapter
Bit-shift algorithm
# cat /proc/bus/i2c-0
cat: read: Invalid argument

    What I don't understand is this problem with /proc/bus/i2c-0.

    Am I right in thinking that this file should contain the addresses
of all the devices on the i2c-0 bus ? and I should be able to read the
file shouldn't I ?

    Ignoring that problem for a moment - if I try to set the slave
address with something like

        if( ( r = ioctl(fd, I2C_SLAVE, addr)) < 0)
                fprintf(stderr, "Error eeprom_open: %s\n",
                return -1;

    then it errors out. This code snippet is from 'eeprog' which is a
simple program to access 24Cxx EEPROM devices available at so I guess should work OK. I assume it
fails because it can't read the file /proc/bus/i2c-0

    So the problem is either with the adaptor I have built or the way
the modules have loaded.

    If I disconnect my adaptor, then I still get problems typing the
contents of /proc/bus/i2c-0 as above.

    Can someone with i2c working please confirm that I should be able to
type out the contents of /proc/bus/i2c-0 and that it contains addresses
of devices on the i2c bus

Re: Got i2c working ? Can you answer this ?
I'll answer my own question here in case someone else comes across the

Basically, it's a bug in the 2.4 kernel.

The bug is in module i2c-core.c and a patch is available. I found it by
using Google and searching for "cat: read: Invalid argument"

I hope this helps someone in the future.


Mike wrote:

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