Raspberry Pi
Setup
Arch Linux
Download ArchLinux's Raspberry Pi tarball.
- Raspberry Pi: http://archlinuxarm.org/os/ArchLinuxARM-rpi-latest.tar.gz
- Raspberry Pi 2: http://archlinuxarm.org/os/ArchLinuxARM-rpi-2-latest.tar.gz
Setup the SD card to contain two partitions using fdisk:
- 100MB (W95 FAT32 (LBA))
- Rest: OS / Data
# fdisk /dev/sdcard
## Set up the SD card partitions
## Commands are: o, n, p, [enter], +100M, t, c, n, p, 2, [enter], [enter], w
# mkfs.vfat /dev/sdcard1
# mkfs.ext4 /dev/sdcard2
# cd /mnt
# mkdir root root/boot
# mount /dev/sdcard2 root
# mount /dev/sdcard1 root/boot
# tar -xpf ArchLinuxARM-rpi-latest.tar.gz -C root
# umount root/boot root
Once the SD card is prepared, insert it to the Pi and power it on. Log in to ArchLinux using the default user alarm using password alarm. The default root password is root.
For more information and to see the latest images see:
- http://archlinuxarm.org/platforms/armv6/raspberry-pi
- http://archlinuxarm.org/platforms/armv7/broadcom/raspberry-pi-2
Configuration
Wi-Fi
Wi-Fi on the Raspberry pi is basically the same as on a linux desktop. See the main page on Wifi.
GPIO
GPIO (General Purpose Input/Output) pins can be interfaced using the GPIO Sysfs on the Linux kernel.
Without going into details, you can interface with GPIO at /sys/class/gpio with these common commands:
| Command | Description |
|---|---|
cat /sys/class/gpio/gpiochip0/ngpio
|
Returns the number of GPIOs managed by this device.
Eg. RPi 1 has More precisely, this device handles GPIOs 0 through 53 (N to N + ngpio - 1). |
cat /sys/class/gpio/gpiochip0/base
|
Returns the first GPIO number. (This should be the same as the number after gpiochipN).
|
echo 11 > /sys/class/gpio/export
|
Exports GPIO 11. Creates a device /sys/class/gpio/gpio11
|
echo in > /sys/class/gpio/gpio11/direction
|
Sets the GPIO to either in or out |
echo 0 > /sys/class/gpio/gpio11/value
|
Writes a binary value to the GPIO |
echo 11 > /sys/class/gpio/unexport
|
Removes GPIO 11. |
If you plan on doing something advance with the GIOs, you probably should use a library instead.
See also:
- https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/Documentation/gpio/gpio.txt
- https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/Documentation/gpio/sysfs.txt
Miscellaneous
Control Status LEDs
The Raspberry Pi 2 (and higher) LEDs are driven by the kernel's led-GPIO drivers. This allows for the LEDs to be controlled by software rather than hardware as is the case with the older first generation Pi's. The two LEDs on the Raspberry Pi 2 are the green status light (led0) and the red power light (led1).
To see the available triggers that are in use and available for a particular LED:
# cat /sys/class/leds/led1/trigger
none usb-gadget usb-host [mmc0] timer oneshot heartbeat backlight gpio cpu0 cpu1 cpu2 cpu3 default-on transient flash torch input
The active trigger is in [ ] and can be changed by writing to the file. For example, to turn off the LED entirely:
# echo none > /sys/class/leds/led1/trigger
# cat /sys/class/leds/led1/trigger
[none] usb-gadget usb-host mmc0 timer oneshot heartbeat backlight gpio cpu0 cpu1 cpu2 cpu3 default-on transient flash torch input
You may also edit the config.txt file to change the behavior on startup.
# Disable the ACT LED.
dtparam=act_led_trigger=none
dtparam=act_led_activelow=off
# Disable the PWR LED.
dtparam=pwr_led_trigger=none
dtparam=pwr_led_activelow=off
See Also: http://www.armadeus.com/wiki/index.php?title=GPIO_LEDS
Mounting /var/log as tmpfs
Append to the /etc/fstab with the following line.
tmpfs /var/log tmpfs nodev,nosuid,mode=0755,size=50m 0 0
This will mount /var/log as a 50MB ramdisk. If your system is using systemd, this will break systemd-journald. To fix it, you will need to create a startup script after the mount has completed that creates the journald's directory in /var/log/journal/.
Reboot the Pi for the changes to take affect, or run mount -a which will mount the ramdisk to /var/log immediately, though you'll need to restart any services that has handles to any files there.
Why would you want to do this? To limit the amount of writes that is made to the SD card to prevent premature wearing.
UART Serial
By default, ArchLinux on the Raspberry Pi will start a getty on the UART serial port. To make use of the port, you will have to disable the getty first.
Edit /boot/cmdline.txt and remove all instances of ttyAMA0. Mine ended up looking like:
root=/dev/mmcblk0p2 rw rootwait console=tty1 selinux=0 plymouth.enable=0 smsc95xx.turbo_mode=N dwc_otg.lpm_enable=0 elevator=noop
Then, run:
systemctl disable serial-getty@ttyAMA0.service
Reboot.
If everything is working, you should be able to talk with /dev/ttyAMA0.
# stty < /dev/ttyAMA0
speed 9600 baud; line = 0;
kill = ^H; min = 100; time = 2;
-icrnl -imaxbel
-opost -onlcr
-isig -icanon -echo
# cat /dev/ttyAMA0 &
# echo hello > /dev/ttyAMA0
If you need to change the baud rate, run stty -F /dev/ttyAMA0 115200