Interesting.  In a separate email, it was suggested I use MCP23017.  I was unaware that there wouldn't be a linux driver for it.

I don't deal with the hardware side of things here, so I'm not sure what voltages things will be run at.  The chart I am going by here lists the MCP23017 connected to GPIO184 (I2C CLK) and GPIO185 (I2C DATA).  Then a separate listing of some buttons that will be on that bus listed as GPA0 - GPA5.  I don't know what GPIOs those GPA numbers would use.  So I'm a bit confused myself.

On Wed, Mar 24, 2010 at 10:20 AM, Dave Hylands <> wrote:

On Wed, Mar 24, 2010 at 7:03 AM,  <> wrote:
> How do I determine if the chip is supported by kernel drivers?  I'm told
> we'll be using the MCP23017.  This is on Gumstix Overo.

I did some googling and there doesn't appear to even be a linux driver
for this chip.

> The pins we were told to use on the expansion board are GPA# instead of
> GPIO### (e.g., GPA0 vs. GPIO171).  If these are exposed in
> /sys/class/gpio/GPA# similarly to GPIOs, that would be great.

I'm confused. Since this is an i2c bus, shouldn't you be connecting it
to the i2c bus on the expansion board? The interrupt line(s) should go
to a GPIO pin, but the SDA and SCL signals on the chip should connect
to the SDA and SCL signals on the board.

Will you be running the part at 1.8v? If so then you won't need any
voltage converters between the chip and the expansion board.

The GPIO pins are exposed in /sys/class only using their GPIO numbers.
You won't see GPA0. You'll see GPIO171.

Dave Hylands
Shuswap, BC, Canada

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