All that is left is to configure your WiFi connection. You can edit this file using the following command:. This will open the file in an editor called nano it is a very simple text editor that is easy to approach and use; even for users not familiar to a linux based operating systems just use the arrow keys. To configure you wireless network you want to modify the file such that it looks like the following:. You will need to put your own SSID and password into the appropriate places.
If nano asks if you want to Save modified buffer? At this point everything is configured — all we need to do is reload the network interfaces.
This can be done by running the following command warning: if you are connected using a remote connection it will disconnect now :. After reloading the network interface and re-connecting to the pi if you are using a remote connection — you can now check the status of our WiFi connection by running:. I think the wireless adapter is not working. You can switch between these modes at any time. If your HDMI monitor or TV has built-in speakers, the audio can be played over the HDMI cable, but you can switch it to a set of headphones or other speakers plugged into the headphone jack.
If your display claims to have speakers, sound is output via HDMI by default; if not, it is output via the headphone jack. This may not be the desired output setup, or the auto-detection is inaccurate, in which case you can manually switch the output.
There are two ways of setting the audio output; using the Desktop volume control, or using raspi-config command line tool. Right-clicking the volume icon on the desktop taskbar brings up the audio output selector; this allows you to select between the internal audio outputs. It also allows you to select any external audio devices, such as USB sound cards and Bluetooth audio devices. The volume control and mute operate on the currently selected device.
Open up raspi-config by entering the following into the command line:. Select System Options Currently option 1, but yours may be different and press Enter. Now select the Option named, Audio Currently option S2, but yours may be different and press Enter :. Select your required mode, press Enter and press the right arrow key to exit the options list, then select Finish to exit the configuration tool.
After you have finished modifying your audio settings, you need to restart your Raspberry Pi in order for your changes to take effect.
In some rare cases, it is necessary to edit config. To set up your storage device so that it always mounts to a specific location of your choice, you must mount it manually. You can mount your storage device at a specific folder location.
Note that the folder must be empty. Your storage device will show up in this list, along with any other connected storage. For example, sda1. If your storage device uses an NTFS file system, you will have read-only access to it.
If you want to write to the device, you can install the ntfs-3g driver:. Create a target folder to be the mount point of the storage device. The mount point name used in this case is mydisk. You can specify a name of your choice:. You can modify the fstab file to define the location where the storage device will be automatically mounted when the Raspberry Pi starts up. In the fstab file, the disk partition is identified by the universally unique identifier UUID.
Replace fstype with the type of your file system, which you found in step 2 of 'Mounting a storage device' above, for example: ntfs. Now that you have set an entry in fstab , you can start up your Raspberry Pi with or without the storage device attached. Before you unplug the device you must either shut down the Pi, or manually unmount it using the steps in 'Unmounting a storage device' below. For more information on each Linux command, refer to the specific manual page using the man command.
For example, man fstab. When the Raspberry Pi shuts down, the system takes care of unmounting the storage device so that it is safe to unplug it.
If you want to manually unmount a device, you can use the following command:. If you receive an error that the 'target is busy', this means that the storage device was not unmounted. If no error was displayed, you can now safely unplug the device. The 'target is busy' message means there are files on the storage device that are in use by a program. To close the files, use the following procedure. If you have a terminal open, make sure that you are not in the folder where the storage device is mounted, or in a sub-folder of it.
If you are still unable to unmount the storage device, you can use the lsof tool to check which program has files open on the device. You need to first install lsof using apt :. If you want to select a different keyboard use raspi-config. Once again, this is something you can change using the raspi-config tool. As of July , the Raspberry Pi firmware supports custom default pin configurations through a user-provided Device Tree blob file.
To find out whether your firmware is recent enough, please run vcgencmd version. Setting by the GPIO command in config. On a soft reset, the same procedure applies, except for default pulls, which are only applied on a power-on reset. Note that it may take a few seconds to get from stage 1 to stage 4. During that time, the GPIO pins may not be in the state expected by attached peripherals as defined in dtblob.
Since different GPIO pins have different default pulls, you should do one of the following for your peripheral:. In order to compile a Device Tree source. The dtc command can then be used as follows:. Similarly, a. The dt-blob. It is not currently used by the Linux kernel, but a kernel section will be added at a later stage, when we reconfigure the Raspberry Pi kernel to use a dt-blob for configuration. The dt-blob can configure all versions of the Raspberry Pi, including the Compute Module, to use the alternative settings.
The following sections are valid in the dt-blob:. This section contains all of the VideoCore blob information. All subsequent sections must be enclosed within this section. There are some differences because of the moved I2C pins.
Each item in this section must be a named pin section, such as pin p32 , meaning GPIO Please note that you can only specify a single drive strength for the bank. This section is used to set specific VideoCore functionality to particular pins. This enables the user to move the camera power enable pin to somewhere different, or move the HDMI hotplug position: things that Linux does not control.
Please refer to the example DTS file below. It is possible to change the configuration of the clocks through this interface, although it can be difficult to predict the results! The configuration of the clocking system is very complex. Each of the clock destinations can be configured to come from one of the clock channels, although there is a restricted mapping of source to destination, so not all channels can be routed to all clock destinations.
Here are a couple of example configurations that you can use to alter specific clocks. We will add to this resource when requests for clock configurations are made. This is used to give an audio codec the Hz it needs to produce the range of frequencies. This is the master Raspberry Pi blob, from which others are usually derived. These Device Trees may include DT parameters that provide a degree of control over some onboard features.
DT overlays allow optional external hardware to be described and configured, and they also support parameters for more control. The firmware loader start. It chooses which one to load based on the board revision number, and makes certain modifications to further tailor it memory size, Ethernet addresses etc.
This runtime customisation avoids the need for lots of DTBs with only minor differences. The loader examines the result to learn for example which UART, if any, is to be used for the console.
Finally it launches the kernel, passing a pointer to the merged DTB. A Device Tree DT is a description of the hardware in a system. It should include the name of the base CPU, its memory configuration, and any peripherals internal and external. A DT should not be used to describe the software, although by listing the hardware modules it does usually cause driver modules to be loaded.
A Device Tree represents the hardware configuration as a hierarchy of nodes. Each node may contain properties and subnodes. Properties are named arrays of bytes, which may contain strings, numbers big-endian , arbitrary sequences of bytes, and any combination thereof. By analogy to a filesystem, nodes are directories and properties are files. DTS syntax is C-like, with braces for grouping and semicolons at the end of each line. Note that DTS requires semicolons after closing braces: think of C struct s rather than functions.
Properties are simple key-value pairs where the value can either be empty or contain an arbitrary byte stream. While data types are not encoded in the data structure, there are a few fundamental data representations that can be expressed in a Device Tree source file. Given that nodes are named, potentially with absolute paths, it is possible for the same node to appear twice in a DTS file and its inclusions. When this happens, the nodes and properties are combined, interleaving and overwriting properties as required later values override earlier ones.
It is thus possible for one. It is often necessary for one part of the tree to refer to another, and there are four ways to do this:. A phandle is a unique bit integer assigned to a node in its phandle property. For historical reasons, you may also see a redundant, matching linux,phandle. They are usually allocated by the DT compiler when it encounters a reference to a node in an integer context, usually in the form of a label see below. References to nodes using phandles are simply encoded as the corresponding integer cell values; there is no markup to indicate that they should be interpreted as phandles, as that is application-defined.
Just as a label in C gives a name to a place in the code, a DT label assigns a name to a node in the hierarchy. Note that labels contain no structure; they are just tokens in a flat, global namespace. Aliases are similar to labels, except that they do appear in the FDT output as a form of index. How to construct a Device Tree, and how best to use it to capture the configuration of some hardware, is a large and complex subject.
There are many resources available, some of which are listed below, but several points deserve mentioning in this document:. When an OS encounters a node with a compatible property, it looks it up in its database of device drivers to find the best match. In Linux, this usually results in the driver module being automatically loaded, provided it has been appropriately labelled and not blacklisted.
The status property indicates whether a device is enabled or disabled. If the status is ok , okay or absent, then the device is enabled. Otherwise, status should be disabled , so that the device is disabled. It can be useful to place devices in a. A derived configuration can then include that. Taking that one step further and placing the SoC on a board with other components only makes matters worse. To keep that manageable, particularly if there are related devices that share components, it makes sense to put the common elements in.
When a system like Raspberry Pi also supports optional plug-in accessories such as HATs, the problem grows. Ultimately, each possible configuration requires a Device Tree to describe it, but once you factor in all the different base models and the large number of available accessories, the number of combinations starts to multiply rapidly.
What is needed is a way to describe these optional components using a partial Device Tree, and then to be able to build a complete tree by taking a base DT and adding a number of optional elements. You can do this, and these optional elements are called "overlays". A DT overlay comprises a number of fragments, each of which targets one node and its subnodes. Although the concept sounds simple enough, the syntax seems rather strange at first:. The compatible string identifies this as being for BCM, which is the base architecture for the Raspberry Pi SoCs; if the overlay makes use of features of a Pi 4 then brcm,bcm is the correct value to use, otherwise brcm,bcm can be used for all Pi overlays.
Then comes the first and in this case only fragment. Fragments should be numbered sequentially from zero. Failure to adhere to this may cause some or all of your fragments to be missed. The example above can be interpreted as if it were written like this:. The effect of merging that overlay with a standard Raspberry Pi base Device Tree e. But if you try to compile this overlay using:. Trying again, this time using the original example and adding the - option to allow unresolved references and -Hepapr to remove some clutter :.
Run sudo apt install device-tree-compiler and try again - this time, compilation should complete successfully.
After the verbose description of the file structure there is our fragment. The compiler has also added a phandle property containing a unique to this overlay small integer to indicate that the node has a label, and replaced all references to the label with the same small integer. This node is the key to how unresolved symbols are dealt with.
In this case, the path is to the 0xffffffff value of target , but fragments can contain other unresolved references which would require additional fixes. This is required because the program performing the merge will have to ensure that phandle numbers are sequential and unique.
Back in section 1. This was useful at one time because providing sufficient aliases allowed very old versions of dtc to be used to build the base DTB files, but fortunately that is ancient history now. To avoid the need for lots of Device Tree overlays, and to reduce the need for users of peripherals to modify DTS files, the Raspberry Pi loader supports a new feature - Device Tree parameters. This permits small changes to the DT using named parameters, similar to the way kernel modules receive parameters from modprobe and the kernel command line.
It contains properties whose names are the chosen parameter names, and whose values are a sequence comprising a phandle reference to a label for the target node, and a string indicating the target property; string, integer cell and boolean properties are supported. String parameters can cause their target properties to grow, shrink, or be created.
In a change from earlier implementations, integer parameters may refer to non-existent properties or to offsets beyond the end of an existing property. Device Tree encodes boolean values as zero-length properties; if present then the property is true, otherwise it is false. They are defined like this:. Note that a property is assigned the value false by not defining it. Boolean parameters are declared like this:. Inverted booleans invert the input value before applying it in the same was as a regular boolean; they are declared similarly, but use!
Byte string properties are arbitrary sequences of bytes, e. MAC addresses. They accept strings of hexadecimal bytes, with or without colons between the bytes. There are some situations where it is convenient to be able to set the same value in multiple locations within the Device Tree.
Rather than the ungainly approach of creating multiple parameters, it is possible to add multiple targets to a single parameter by concatenating them, like this:. As seen in 2. The addition of embedded literal assignments allows a parameter to write arbitrary values, regardless of the parameter value supplied by the user. Lines 1, 2 and 4 are fairly obvious, but line 3 is more interesting because the value appears as an integer cell value.
The DT compiler evaluates integer expressions at compile time, which might be convenient particularly if macro values are used , but the cell can also contain a reference to a label:. When the overlay is applied, the label will be resolved against the base DTB in the usual way. Note that it is a good idea to split multi-part parameters over multiple lines like this to make them easier to read - something that becomes more necessary with the addition of cell value assignments like this.
Bear in mind that parameters do nothing unless they are applied - a default value in a lookup table is ignored unless the parameter name is used without assigning a value. Lookup tables allow parameter input values to be transformed before they are used. The DT parameter mechanism as described has a number of limitations, including no easy way to create arrays of integers and the inability to create new nodes.
One way to overcome some of these limitations is to conditionally include or exclude certain fragments. The parameter declaration syntax has been extended to allow the otherwise illegal zero target phandle to indicate that the following string contains operations at fragment or overlay scope.
So far, four operations have been implemented:. A few property names, when targeted by a parameter, get special handling. One you may have noticed already - status - which will convert a boolean to either okay for true and disabled for false. Assigning to the bootargs property appends to it rather than overwriting it - this is how settings can be added to the kernel command line. The reg property is used to specify device addresses - the location of a memory-mapped hardware block, the address on an I2C bus, etc.
The names of child nodes should be qualified with their addresses in hexadecimal, using as a separator:. When assigning to the reg property, the address portion of the parent node name will be replaced with the assigned value. This can be used to prevent a node name clash when using the same overlay multiple times - a technique used by the i2c-gpio overlay. Like the reg property, this can be used to give nodes unique names.
The introduction of the Pi 4, built around the BCM SoC, brought with it many changes; some of these changes are additional interfaces, and some are modifications to or removals of existing interfaces. There is therefore a need for a method of tailoring an overlay to multiple platforms with differing hardware. Supporting them all in a single. A simpler solution is to add a facility to map an overlay name to one of several implementation files depending on the current platform.
The overlay map, which is rolling out with the switch to Linux 5. This is an edited version of the current map file see the full version :. Each node has the name of an overlay that requires special handling. The properties of each node are either platform names or one of a small number of special directives.
A platform name with no value an empty property indicates that the current overlay is compatible with the platform; for example, vc4-kms-v3d is compatible with the bcm platform. A non-empty value for a platform is the name of an alternative overlay to use in place of the requested one; asking for vc4-kms-v3d on BCM results in vc4-kms-v3d-pi4 being loaded instead.
The second example node - vc4-kms-v3d-pi4 - could be inferred from the content of vc4-kms-v3d , but that intelligence goes into the construction of the file, not its interpretation.
In the event that a platform is not listed for an overlay, one of the special directives may apply:. The renamed directive indicates the new name of the overlay which should be largely compatible with the original , but also logs a warning about the rename. The deprecated directive contains a brief explanatory error message which will be logged after the common prefix overlay ' Remember: only exceptions need to be listed - the absence of a node for an overlay means that the default file should be used for all platforms.
The dtoverlay and dtmerge utilities have been extended to support the map file:. For further examples, there is a large collection of overlay source files hosted in the Raspberry Pi Linux GitHub repository.
The overlay handling in the firmware and the run-time overlay application using the dtoverlay utility treat labels defined in an overlay as being private to that overlay. This avoids the need to invent globally unique names for labels which keeps them short , and it allows the same overlay to be used multiple times without clashing provided some tricks are used - see Special properties. Sometimes, however, it is very useful to be able to create a label with one overlay and use it from another.
When this overlay is applied, the loader strips out all symbols except those that have been exported, in this case public , and rewrites the path to make it relative to the target of the fragment containing the label. In older firmware, fragments are applied strictly in order, top to bottom. With firmware released since 14th February , fragments are applied in two passes:.
On a Raspberry Pi it is the job of the loader one of the start. The base Device Trees are located alongside start. This selection is automatic, and allows the same SD card image to be used in a variety of devices. This configuration will cause bcmrpi-b. If these files are copied with the kernel, then the loader will attempt to load one of those DTBs by default. In order to manage Device Tree and overlays, the loader supports a number of config.
It will then search for parameters foo and level , and assign the indicated values to them. The loader will also search for an attached HAT with a programmed EEPROM, and load the supporting overlay from there - either directly or by name from the "overlays" directory; this happens without any user intervention. With a Device Tree, the kernel will automatically search for and load modules that support the indicated enabled devices. Note, however, that layered modules such as i2c-dev still need to be loaded explicitly.
In use, parameters look like this:. If you have an overlay that defines some parameters, they can be specified either on subsequent lines like this:. Overlay parameters are only in scope until the next overlay is loaded. To expose the parameter exported by the base DTB instead, end the current overlay scope using:. Raspberry Pi boards have two I2C interfaces.
However, there are two early revisions of the Model B that have those roles reversed. To make it possible to use one set of overlays and parameters with all Pis, the firmware creates some board-specific DT parameters. These are:. For people writing overlays, the same aliasing has been applied to the labels on the I2C DT nodes. Thus, you should write:.
The EEPROM includes any DT overlay required to enable the board or the name of an overlay to load from the filing system , and this overlay can also expose parameters. As of Linux 4. Compatible kernels manage a stack of overlays that are applied on top of the base DTB. The use of the word "stack" above is important - overlays can only be added and removed at the top of the stack; changing something further down the stack requires that anything on top of it must first be removed.
Use dtoverlay -h to get usage information:. Unlike the config. Command variants that change kernel state adding and removing things require root privilege, so you may need to prefix the command with sudo.
In usage it is largely equivalent to dtoverlay with an overlay name of - , but there are a few differences:. Help on the dtparam command is still available using dtparam -h. The creation or deletion of a device object is triggered by a node being added or removed, or by the status of a node changing from disabled to enabled or vice versa. Beware - the absence of a "status" property means the node is enabled. If you want to change the properties of an existing node, create a fragment that targets it.
Removing an overlay can cause a kernel exception if it deletes a codec that is still being used by a sound card. Experimentation found that devices are deleted in the reverse of fragment order in the overlay, so placing the node for the card after the nodes for the components allows an orderly shutdown. The loading of overlays at runtime is a recent addition to the kernel, and so far there is no accepted way to do this from userspace.
By hiding the details of this mechanism behind commands the aim is to insulate users from changes in the event that a different kernel interface becomes standardised. Some overlays work better at run-time than others. Parts of the Device Tree are only used at boot time - changing them using an overlay will not have any effect.
Applying or removing some overlays may cause unexpected behaviour, so it should be done with caution. This is one of the reasons it requires sudo. To enable overlays for sound cards to be removed, the lxpanelctl utility has been given two new options - alsastop and alsastart - and these are called from the auxiliary scripts dtoverlay-pre and dtoverlay-post before and after overlays are loaded or unloaded, respectively.
Removing an overlay will not cause a loaded module to be unloaded, but it may cause the reference count of some modules to drop to zero. Running rmmod -a twice will cause unused modules to be unloaded. Overlays have to be removed in reverse order. The commands will allow you to remove an earlier one, but all the intermediate ones will be removed and re-applied, which may have unintended consequences. Only Device Tree nodes at the top level of the tree and children of a bus node will be probed.
For nodes added at run-time there is the further limitation that the bus must register for notifications of the addition and removal of children. It is therefore recommended for overlays to place fixed-clock nodes in the root of the tree unless it is guaranteed that the overlay will not be used at run-time. As it is too time-consuming to document the individual overlays here, please refer to the README file found alongside the overlay.
It is kept up-to-date with additions and changes. The loader will skip over missing overlays and bad parameters, but if there are serious errors, such as a missing or corrupt base DTB or a failed overlay merge, then the loader will fall back to a non-DT boot. Otherwise, your driver is probably missing either:. Alongside the dtoverlay and dtparam commands is a utility for applying an overlay to a DTB - dtmerge. To use it you first need to obtain your base DTB, which can be obtained in one of two ways:.
This will include any overlays and parameters you have applied so far, either in config. The solution to this is to use dtmerge to make the copy:.
The Utils repo includes another DT utility - ovmerge. Unlike dtmerge , ovmerge combines file and applies overlays in source form. Because the overlay is never compiled, labels are preserved and the result is usually more readable. It also has a number of other tricks, such as the ability to list the order of file inclusion.
Since the switch to the 4. However, for bare metal and other OSs, the method of disabling DT usage is to add:. By default the firmware will choose a suitable place. By default the device tree can grow to the end of usable memory, which is almost certainly what is required. In some cases this is a performance hit, so it is off by default.
The author can usually be found on Raspberry Pi forums, particularly the Device Tree forum. The Linux kernel accepts a command line of parameters during boot. On the Raspberry Pi, this command line is defined in a file in the boot partition, called cmdline. This is a simple text file that can be edited using any text editor, e. It will not be exactly the same as that in cmdline. There are many kernel command line parameters, some of which are defined by the kernel.
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