User Tools

Site Tools


Raspberry Pi

The Raspberry Pi is single-board computer without an Ethernet Network Switch. There are many more Single-board computers without one.

OpenWrt for Raspberry Pi is compiled with the ARM soft-float kernel ABI. This means that non-integer math is done in software instead of in hardware. Soft float (armel) is slower than hard float (armhf).

Supported Versions

The Raspberry Pi is supported in the brcm2708 target. Releases with support for this target are:

Release Date Version Download
2014-10-02 14.07 Barrier Breaker
2013-04-25 12.09 Attitude Adjustment
2012-07-24 Trunk r32825 - Add support for Raspberry Pi / brcm2708 / 2835

If you are not sure which file to get, download openwrt-brcm2708-sdcard-vfat-ext4.img

Hardware Specifications

All Versions

System-on-Chip CPU Serial JTag Power Connector
Broadcom BCM2835 700 MHz ARM11 ARM1176JZF-S via GPIO via GPIO MicroUSB A

Model Specific Differences

RPi Model RAM Network USB Memory Card Video Audio Power Requirements GPIO Pins
A 256 MB None 1 USB port SD Card HDMI and Composite RCA 3.5mm Stereo 5V 300mA (see below) 8
B 256 or 512 MB 10M/100M Ethernet RJ45 2 USB ports SD Card HDMI and Composite RCA 3.5mm Stereo 5V 700mA (see below) 8
B+ 512 MB 10M/100M Ethernet RJ45 4 USB ports MicroSD HDMI and shared TRSS 3.5mm Shared TRSS 3.5mm 5V 600mA (see below) 17

Power Notes

The power figures quoted are the bare minimum to run the SoC with no peripherals. Most people find at least a solid 1A is required, especially if adding USB peripherals like keyboard, mouse, or wifi.

A popular power supply is the Apple 12W iPad charger, supplying 5V 2.4A. Similar high-powered mobile phone and tablet chargers should suffice. Using cheap power supplies off eBay is not recommended, as they provide a very uneven and noisy current which can lead to unreliable operation.

It is possible to back-power some Raspberry Pi models from the USB ports, however this is not recommended, as the power in from the USB ports is not protected against surges whereas the main power supply is protected.

It is also possible to supply the required power via the GPIO pins.


Serial is available via GPIO.

Pin 6 Pin 8 Pin 10
Ground TX RX

Connect via RS232 at 3.3 Volts (not older 12V). 115200 bps 8N1.

How to flash OpenWrt to an SD card

On a Linux desktop, insert your SD card and run:


to see the latest kernel messages.

The most recent message should give you the SD card's device name, such as sdb or sdf or similar.

Download the relevant openwrt-brcm2708-sdcard-vfat-ext4.img image.

As the root user, use dd to copy the image file to the device you identified previously, for example:

dd if=/home/username/Downloads/openwrt-brcm2708-sdcard-vfat-ext4.img of=/dev/sdX bs=2M conv=fsync

Replace the sdX with your device name, such as sdb or sdf.

On a Windows desktop, use Win32DiskImager to copy the img file to your SD card's drive letter.

There are many more complex guides around the internet to flashing images to SD cards,



toh/raspberry_pi.txt · Last modified: 2014/10/20 03:55 by gslurp