7.5 KiB
Audio
alsa-utils should supply the needed programs to use onboard sound. Default
volume can be adjusted using alsamixer.
A key change with Linux kernel version 4.4.x for ARM related to ALSA and to the
needed sound module: in order to use tools such as alsamixer with the current
kernel, users must modify /boot/config.txt to contain the following line:
dtparam=audio=on
Caveats for Audio
To force audio over HDMI, add this to /boot/config.txt:
hdmi_drive=2
If you experience distortion using the 3.5mm analogue output:
audio_pwm_mode=2
Video
The X.org driver for Raspberry Pi can be installed with the xf86-video-fbdev
or xf86-video-fbturbo-git package.
CPU/GPU RAM split
Memory split between the CPU and GPU can be set in boot/config.txt
by adjusting the parameter gpu_mem which stands for the amount of RAM in MB
that is available to the GPU (minimum 16, default 64) and the rest is available
to the ARM CPU.
HDMI/Analogue TV-Out
With the default configuration, the Raspberry Pi uses HDMI video if a HDMI
monitor is connected. Otherwise, it uses analog TV-Out (also known as composite
output or RCA) To turn the HDMI or analog TV-Out on or off, have a look at
/opt/vc/bin/tvservice
Use the -s parameter to check the status; the -o
parameter to turn the display off and -p parameter to power on HDMI with
preferred settings.
Adjustments are likely required to correct proper
overscan/underscan and are easily achieved in /boot/config.txt in which many
tweaks are set. To fix, simply uncomment the corresponding lines and setup per
the commented instructions:
# uncomment the following to adjust overscan. Use positive numbers if console
# goes off screen, and negative if there is too much border
#overscan_left=16
overscan_right=8
overscan_top=-16
overscan_bottom=-16
Or simply disable overscan if the TV/monitor has a "fit to screen" option.
disable_overscan=1
Users wishing to use the analog video out should consult this config file which contains options for non-NTSC outputs.
Camera
The commands for the camera module are included as part of the raspberrypi-firmware package:
$ /opt/vc/bin/raspistill
$ /opt/vc/bin/raspivid
Append to /boot/config.txt:
gpu_mem=128
start_file=start_x.elf
fixup_file=fixup_x.dat
Optionally
disable_camera_led=1
The following is a common error:
mmal: mmal_vc_component_enable: failed to enable component: ENOSPC
mmal: camera component couldn't be enabled
mmal: main: Failed to create camera component
mmal: Failed to run camera app. Please check for firmware updates
which can be corrected by setting these values in /boot/config.txt:
cma_lwm=
cma_hwm=
cma_offline_start=
Another common error:
mmal: mmal_vc_component_create: failed to create component 'vc.ril.camera' (1:ENOMEM)
mmal: mmal_component_create_core: could not create component 'vc.ril.camera' (1)
mmal: Failed to create camera component
mmal: main: Failed to create camera component
mmal: Only 64M of gpu_mem is configured. Try running "sudo raspi-config" and ensure that "memory_split" has a value of 128 or greater
can be corrected by adding the following line to /etc/modprobe.d/blacklist.conf:
blacklist i2c_bcm2708
In order to use standard applications (those that look for /dev/video0) the
V4L2 driver must be loaded. This can be done automatically at boot by creating
an autoload file, /etc/modules-load.d/rpi-camera.conf:
bcm2835-v4l2
The V4L2 driver by default only allows video recording up to 1280x720, else it
glues together consecutive still screens resulting in videos of 4 fps or lower.
Adding the following options removes this limitation, /etc/modprobe.d/rpi-camera.conf:
options bcm2835-v4l2 max_video_width=3240 max_video_height=2464
Onboard Hardware Sensors
Temperature
Temperatures sensors can be queried with utils in the raspberrypi-firmware package.
$ /opt/vc/bin/vcgencmd measure_temp
temp=49.8'C
Voltage
Four different voltages can be monitored via /opt/vc/bin/vcgencmd:
$ /opt/vc/bin/vcgencmd measure_volts <id>
Where <id> is:
- core for core voltage
- sdram_c for sdram Core voltage
- sdram_i for sdram I/O voltage
- sdram_p for sdram PHY voltage
Watchdog
BCM2708 has a hardware watchdog which can be utilized by enabling the
bcm2708_wdog kernel module.
For proper operation the watchdog daemon also has to be installed, configured
(by uncommenting the "watchdog-device" line in /etc/watchdog.conf) and
enabled.
This should also apply for Raspberry Pi 2 by using the bcm2709_wdog module
and Raspberry Pi 3 by using the bcm2835_wdt module.
Hardware Random Number Generator
Arch Linux ARM for the Raspberry Pi had the bcm2708-rng module set to load at
boot; starting with kernel 4.4.7 the bcm2835_rng module replaces the
former on Raspberry Pi 2 and Raspberry Pi 3 units.
Install rng-tools and
tell the Hardware RNG Entropy Gatherer Daemon (rngd) where to find the hardware
random number generator. This can be done by editing /etc/conf.d/rngd:
RNGD_OPTS="-o /dev/random -r /dev/hwrng"
and enabling and starting the rngd service.
If haveged is running, it should be stopped and disabled, as it might
compete with rngd and is only preferred when there is no hardware random number
generator available.
Once completed, this change ensures that data from the
hardware random number generator is fed into the kernel's entropy pool at
/dev/random. To check the available entropy, run:
# cat /proc/sys/kernel/random/entropy_avail
The number it reports should be around 3000, whereas before setting up rngd it would have been closer to 1000.
I/O Pins
GPIO
To be able to use the GPIO pins from Python, use the RPi.GPIO library. Install the python-raspberry-gpio package from the AUR.
SPI
To enable the /dev/spidev* devices, uncomment the following line in
/boot/config.txt:
device_tree_param=spi=on
I2C
Install i2c-tools and lm_sensors packages.
Configure the bootloader to enable the i2c hardware by appending to /boot/config.txt:
dtparam=i2c_arm=on
Configure the i2c-dev and i2c-bcm2708 (if not blacklisted for the camera) modules to be loaded at boot in
/etc/modules-load.d/raspberrypi.conf:
i2c-dev i2c-bcm2708
Reboot the Raspberry Pi and issue the following command to get the hardware address:
i2cdetect -y 0
Note: When using the I2C1 port instead of I2C0, one will need to run i2cdetect -y 1 instead and replace i2c-0 with i2c-1 in the following steps.
Now instantiate the device. Change the hardware address to the address found in the previous step with '0x' as prefix (e.g. 0x48) and choose a device name:
echo <devicename> <hardware address> >/sys/class/i2c-adapter/i2c-0/new_device
Check dmesg for a new entry:
i2c-0: new_device: Instantiated device ds1621 at 0x48
Finally, read the sensor output: sensors
1-WIRE
To enable the 1-wire interface add this line to /boot/config.txt and reboot.
dtoverlay=w1-gpio
See Also
- Raspberry Pi - Official website
- RPi Config - Excellent source of info relating to under-the-hood tweaks.
- RPi vcgencmd usage - Overview of firmware command vcgencmd.
- Arch Linux ARM on Raspberry Pi - A FAQ style site with hints and tips for running Arch Linux on the RPi