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