Re: Raspberry Pi & i2c bus

["Jonathan A. Kollasch" <jakllsch%kollasch.net@localhost>]

On Tue, Jan 15, 2013 at 11:37:05PM +0000, Dave Tyson wrote:
> Very impressed with progress so on the Raspberry Pi so I though I would try 
> some more challenging tests :-)
> 
> I have been trying to couple up a BMP085 pressure sensor to the I2C bus on 
> the 
> RPI. I have tested it under raspian and it seems to work OK, but I am having 
> a 
> few issues with NetBSD (latest kernel 6.99.16 compiled yesterday)
> 
> First problem is i2cscan reports rather more devices on the bus than actually 
> exist:
> 
>  /usr/sbin/i2cscan /dev/iic0
> /dev/iic0: found device at 0x09
> /dev/iic0: found device at 0x0a
> /dev/iic0: found device at 0x0b
> /dev/iic0: found device at 0x0d
> /dev/iic0: found device at 0x0e
> /dev/iic0: found device at 0x0f
> ...
> /dev/iic0: found device at 0x71
> /dev/iic0: found device at 0x72
> /dev/iic0: found device at 0x73
> /dev/iic0: found device at 0x74
> /dev/iic0: found device at 0x75
> /dev/iic0: found device at 0x76
> /dev/iic0: found device at 0x77
> /dev/iic0: 80 devices found
> 
> The same thing happens on /dev/iic1 which has nothing attached...
> 
> The BMP085 transducer is hard wired at addr 0x77 and under raspian that's all 
> that is reported on iic0. C code to read the device just failed EIO, so I 
> simplified it to just try and read just the top byte of the first calibration 
> register. That failed EIO. Turning on debugging in bcm2835_bsc.c showed that 
> the actual error was CLKT and the slave is clock stretching longer that 
> specified. 
> 
> The 9 pages of publically available Broadcom documentation on this part of 
> the 
> BSC controller is a complete joke. Has anyone had any success with devices on 
> this bus? Is there any more sensible documentation with maybe some state 
> diagrams or timing :-)

I only tested bcmbsc(4) with a PCF8583.  I never tried anything via the
/dev/iic interface.  I agree, the docs are lacking, I had to fall back
to the Linux implementation for clues.

        Jonathan Kollasch