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doc/driver-guide.md : Fix typo, punctuations and sentences
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@ -25,27 +25,26 @@ However, please avoid the use of `float` or `double`. Instead, multiply to the
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next SI (or appropriate) unit. E.g. if an ADC would return values like `1.23 V`,
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next SI (or appropriate) unit. E.g. if an ADC would return values like `1.23 V`,
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chose to return `1230 mV` instead.
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chose to return `1230 mV` instead.
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Additionally towards ease of use, all device drivers in RIOT should provide a
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Additionally, towards ease of use, all device drivers in RIOT should provide a
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similar 'look and feel'. They should behave similar concerning things like their
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similar 'look and feel'. They should behave similarly in terms of their state
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state after initialization, like their used data representation and so on.
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after initialization, like their used data representation and so on.
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Secondly, all device drivers should be optimized for minimal RAM/ROM usage, as
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Secondly, all device drivers should be optimized for minimal RAM/ROM usage, as
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RIOT targets (very) constrained devices. This implies, that instead of exposing
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RIOT targets (very) constrained devices. This implies that instead of exposing
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all thinkable functionality, the drivers should focus on exporting and
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all thinkable functionality, the drivers should focus on exporting and
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implementing a device's core functionality, thus covering ~95% of the use cases.
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implementing a device's core functionality, thus covering ~95% of the use cases.
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Furthermore great care should be put into ...(?)
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Third, it should always be possible, to handle more than a single device of one
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Third, it should always be possible to handle more than a single device of the
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kind. Drivers and their interfaces are thus designed to keep their state
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same kind. Drivers and their interfaces are thus designed to keep their state
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information in a parameterized location instead of driver defined global
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information in a parameterized location instead of driver defined global
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variables.
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variables.
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Fourth, RIOT defines high-level interfaces for certain groups of devices (i.e.
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Fourth, RIOT defines high-level interfaces for certain groups of devices (i.e.
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netdev for network devices, SAUL for sensors and actuators), which enable users
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netdev for network devices, SAUL for sensors and actuators), which enable users
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to work with a wide variety of devices without having to know anything about the
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to work with a wide variety of devices without having to know much about the
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actual device that is mapped.
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actual device that is mapped.
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Fifth, during initialization we make sure that we can communicate with a device.
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Fifth, during initialization, we make sure that we can communicate with a device.
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Other functions should check the dev pointer is not void, and should also handle
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Other functions should check the dev pointer is not void, and should also handle
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error return values from the lower layer peripheral driver implementations,
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error return values from the lower layer peripheral driver implementations,
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where there are some.
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where there are some.
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@ -59,8 +58,8 @@ platform independent interfaces as the peripheral drivers, xtimer, etc.
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## Documentation {#driver-guide-doc}
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## Documentation {#driver-guide-doc}
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Document what your driver does! Most devices come with a very large number of
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Document what your driver does! Most devices come with a very large number of
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features, while the corresponding device driver only supports a sub-set of them.
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features, while the corresponding device driver only supports a subset of them.
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This should be clearly stated in the device driver's documentation, so that
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This should be clearly stated in the device driver's documentation so that
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anyone wanting to use the driver can find out the supported features without
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anyone wanting to use the driver can find out the supported features without
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having to scan through the code.
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having to scan through the code.
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@ -72,7 +71,7 @@ configuration, using the naming scheme of `DEVNAME_t` (e.g. `dht_t`, or
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descriptor.
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descriptor.
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This device descriptor MUST contain all the state data of a device. By this, we
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This device descriptor MUST contain all the state data of a device. By this, we
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are not limited on the number of instances of the driver we can run
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are not limited to the number of instances of the driver we can run
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concurrently. The descriptor is hereby used for identifying the device we want
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concurrently. The descriptor is hereby used for identifying the device we want
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to interact with, and SHOULD always be the first parameter for all device driver
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to interact with, and SHOULD always be the first parameter for all device driver
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related functions.
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related functions.
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@ -87,7 +86,7 @@ is `DEVNAME_params_t`. In contrary to the device descriptor, this data structure
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should only contain static information, that is needed for the device
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should only contain static information, that is needed for the device
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initialization as it is preferably allocated in ROM.
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initialization as it is preferably allocated in ROM.
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A simple I2C temperature sensors's device descriptor could look like this:
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A simple I2C temperature sensors' device descriptor could look like this:
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@code{.c}
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@code{.c}
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typedef struct {
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typedef struct {
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@ -103,8 +102,8 @@ typedef struct {
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@endcode
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@endcode
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**NOTE:** In many cases it makes sense, to copy the `xxx_params` data into the
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**NOTE:** In many cases it makes sense, to copy the `xxx_params` data into the
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device descriptor during initialization. In some cases, it is however better to
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device descriptor during initialization. In some cases, it is, however, better
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just link the `params` data via pointer and only copy selected data. This way,
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to just link the `params` data via pointer and only copy selected data. This way,
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configuration data that is only used once can be read directly from ROM, while
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configuration data that is only used once can be read directly from ROM, while
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often used fields (e.g. used peripherals) are stored directly in the device
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often used fields (e.g. used peripherals) are stored directly in the device
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descriptor and one saves hereby one de-referencing step when accessing them.
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descriptor and one saves hereby one de-referencing step when accessing them.
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@ -113,7 +112,7 @@ descriptor and one saves hereby one de-referencing step when accessing them.
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Each device driver in RIOT MUST supply a default configuration file, named
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Each device driver in RIOT MUST supply a default configuration file, named
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`DEVNAME_params.h`. This file should be located in the `RIOT/drivers/...`. The
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`DEVNAME_params.h`. This file should be located in the `RIOT/drivers/...`. The
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idea is, that this file can be overridden by an application or a board, by
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idea is that this file can be overridden by an application or a board, by
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simply putting a file with the same name in the application's or the board's
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simply putting a file with the same name in the application's or the board's
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include folders, while RIOT's build system takes care of preferring those files
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include folders, while RIOT's build system takes care of preferring those files
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instead of the default params file.
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instead of the default params file.
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@ -233,19 +232,19 @@ Sub-groups defined for different types of drivers can be found in
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## Initialization {#driver-guide-initialization}
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## Initialization {#driver-guide-initialization}
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In general, the initialization functions should to the following:
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In general, the initialization functions should do the following:
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- initialize the device descriptor
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- initialize the device descriptor
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- initialize non-shared peripherals they use, e.g. GPIO pins
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- initialize non-shared peripherals they use, e.g. GPIO pins
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- test for device connectivity, e.g. does a SPI/I2C slave react
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- test for device connectivity, e.g. does an SPI/I2C slave react
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- reset the device to a well defined state, e.g. use external reset lines or do
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- reset the device to a well-defined state, e.g. use external reset lines or do
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a software rest
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a software rest
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- do the actual device initialization
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- do the actual device initialization
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For testing a device's connectivity, it is recommended to read certain
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For testing a device's connectivity, it is recommended to read certain
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configuration data with a defined value from the device. Some devices offer
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configuration data with a defined value from the device. Some devices offer
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`WHO_AM_I` or `DEVICE_ID` registers for this purpose. Writing and reading back
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`WHO_AM_I` or `DEVICE_ID` registers for this purpose. Writing and reading back
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some data to the device is another valid option for testing it's responsiveness.
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some data to the device is another valid option for testing its responsiveness.
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For more detailed information on how the signature of the init functions should
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For more detailed information on how the signature of the init functions should
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look like, please refer below to the specific requirements for network devices
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look like, please refer below to the specific requirements for network devices
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@ -253,10 +252,10 @@ and sensors.
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## Return values {#driver-guide-return-values}
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## Return values {#driver-guide-return-values}
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As stated above, we check communication of a device during initialization, and
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As stated above, we check communication of a device during initialization and
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handle error return values from the lower layers, where they exist. To prevent
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handle error return values from the lower layers, where they exist. To prevent
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subsequent misuse by passing NULL pointers and similar to the subsequent
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subsequent misuse by passing NULL pointers and similar to the subsequent
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functions, the recommended way is to check parameter using `assert`, e.g.:
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functions, the recommended way is to check the parameter using `assert`, e.g.:
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@code{.c}
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@code{.c}
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int16_t tmpabc_read(const tmpabc_t *dev)
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int16_t tmpabc_read(const tmpabc_t *dev)
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@ -267,7 +266,7 @@ int16_t tmpabc_read(const tmpabc_t *dev)
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}
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}
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@endcode
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@endcode
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Whenever status/error return values are implemented by you in your driver, they
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Whenever you implement status/error return values in your driver, they
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should be named, meaning that the driver MUST define an enum assigning names to
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should be named, meaning that the driver MUST define an enum assigning names to
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the actual used value, e.g.
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the actual used value, e.g.
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@ -311,7 +310,7 @@ Then answer a few questions about the driver:
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- Driver name: enter a name for your driver. It will be used as both the name
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- Driver name: enter a name for your driver. It will be used as both the name
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of the driver directory where the source files are created and the build
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of the driver directory where the source files are created and the build
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system module.
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system module.
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- Driver doxygen group name: Enter the name of driver, as displayed in the
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- Driver doxygen group name: Enter the name of the driver, as displayed in the
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Doxygen documentation.
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Doxygen documentation.
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- Brief doxygen description: Describe in one line what is this driver about.
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- Brief doxygen description: Describe in one line what is this driver about.
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- Parent driver Doxygen group: Enter the Doxygen group the driver belongs to.
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- Parent driver Doxygen group: Enter the Doxygen group the driver belongs to.
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@ -379,7 +378,7 @@ preferred type where applicable.
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In many situations, the physical values cannot be mapped directly to integer
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In many situations, the physical values cannot be mapped directly to integer
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values. For example, we do not want to map temperature values to integers
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values. For example, we do not want to map temperature values to integers
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directly while using their fraction. The recommended way to solve this is by
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directly while using their fraction. The recommended way to solve this is by
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scaling the result value using decimal fixed point arithmetic, in other words
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scaling the result value using decimal fixed point arithmetic, in other words,
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just return centi-degree instead of degree (e.g. 2372c°C instead of 23.72°C).
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just return centi-degree instead of degree (e.g. 2372c°C instead of 23.72°C).
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## Additional Sensor Driver Checklist {#driver-guide-sensor-checklist}
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## Additional Sensor Driver Checklist {#driver-guide-sensor-checklist}
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@ -404,7 +403,7 @@ just return centi-degree instead of degree (e.g. 2372c°C instead of 23.72°C).
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## Initialization {#driver-guide-netdev-init}
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## Initialization {#driver-guide-netdev-init}
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The initialization process MUST be split into 2 steps: first initialize the
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The initialization process MUST be split into 2 steps: first, initialize the
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device descriptor and if applicable the used peripherals, and secondly do the
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device descriptor and if applicable the used peripherals, and secondly do the
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actual device initialization. The reason for this is, that before a device is
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actual device initialization. The reason for this is, that before a device is
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actually activated and can start to process data, the network stack for the
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actually activated and can start to process data, the network stack for the
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