Rpi Low-level peripherals

The Rpi allows peripherals to access the CPU by exposing the in and outputs. The production board has a 26-pin 1.27mm (50mil) expansion header, arranged in a 2x13 strip. They provide 8 GPIO pins plus access to I2C, SPI, UART), as well as +3V3, +5V and GND supply lines. Pin one is column 0 on the bottom row.

Voltage levels are 3v3. There is no over-voltage protection on the board - the intention is that people interested in serious interfacing will use an external board with buffers, level conversion and analog I/O rather than soldering directly onto the main board.

It is also possible to reconfigure some of the pins to provide a second I2C interface. [no-ref]

Kernel boot messages go to the UART at 115200bps.

Pinout:

Colour-coded Image: https://sites.google.com/site/burngatehouse/home/drawings/GPIOs.gif

Power pins
Maximum permitted current draw from the 3v3 pin is 50mA. Maximum permitted current draw from the 5v pin is the USB input current (usually 1A) minus any current draw from the rest of the board, or about 500mA for model A, or 700mA for B.

General Purpose Input/Output (GPIO)
General Purpose Input/Output (a.k.a. GPIO) is a generic pin on a chip whose behavior (including whether it is an input or output pin) can be controlled (programmed) through software. For more information see:the wikipedia article.

On the production board, all the UART, SPI and I2C pins can be reconfigured as GPIO pins, to provide a total of 17 GPIO pins.

At least some of the GPIO pins support PWM.

Each GPIO can interrupt, high/low/rise/fall/change.

It is also possible to reconfigure some of the pins to provide an ARM JTAG interface.

It is also possible to reconfigure some of the pins to provide an I2S or PCM interface.

Driver support
The Foundation will not include a GPIO driver in the initial release, standard linux GPIO drivers should work with minimal modification. The Foundation will not include a SPI driver in the initial release, we hope the community might write one. The Foundation will not include an I2C driver in the initial release, we hope the community might provide one, standard linux I2C drivers should work with minimal modification.

Code examples
Here, some code examples should be shown.

MIPI CSI-2
On the production board, we bring out the MIPI CSI-2 interface to pads for an unpopulated 15-way flat flex connector

DSI
On the production board, we bring out the DSI interface to pads for an unpopulated 15-way flat flex connector

CEC
HDMI-CEC is supported by hardware but some driver work will be needed and currently isn't exposed into Linux userland. Eben notes that he has seen CEC demos on the Broadcom SoC they are using.