Add dualcam and pin configuration documentation

[XECDesign]

No description provided.

[lurch]

AFAICT (it's a bit of an educated guess) the GPIOs listed under the instructions for connecting the second camera in cmio-camera.md are wrong, and should in fact be GPIO30 and GPIO31 rather than GPIO5 and GPIO 21 ?

[XECDesign]

Yup, well spotted. Fixed

[lurch]

Hmm, just noticed that the device-tree stuff allows you to configure the drive strength on a per-pin basis, whereas everything else I've seen says that the drive strength is only configurable per-bank. Does the firmware simply set the bank drive strength to the max-requested drive strength from all the pins in that bank?

Is there any (pending) documentation for what the valid values for the 'function' strings in the device-tree are?

[popcornmix]

The firmware sets the drive strength to the max of all drive strengths within the bank.

It may make more sense to pull the drive strength attribute out to a per bank setting, but per-pin is how gpioman works on other platforms, so that's how it currently behaves.

[XECDesign]

There's definitely more documentation coming, but for what it's worth, here are the valid function values:
input output sdcard i2c0 i2c1 spi spi1 spi2 smi dpi pcm pwm uart0 uart1 gp_clk te ring_osc emmc arm_jtag flash dvi spi_slave. Some of these are a little 'strange' and not worth worrying about, but I've included them for the sake of it.

[lurch]

Thanks for the info! I've just added a DeviceTree 'function' column to the second table on http://elinux.org/RPi_BCM2835_GPIOs