302 lines
8.0 KiB
ReStructuredText
302 lines
8.0 KiB
ReStructuredText
==============
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Device Drivers
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==============
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NuttX supports a variety of device drivers, which can be broadly
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divided in three classes:
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.. toctree::
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:maxdepth: 1
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character/index.rst
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block/index.rst
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special/index.rst
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.. note::
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Device driver support depends on the *in-memory*, *pseudo*
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file system that is enabled by default.
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Lower-half and upper-half
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=========================
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Drivers in NuttX generally work in two distinct layers:
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* An *upper half* which registers itself to NuttX using
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a call such as :c:func:`register_driver` or
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:c:func:`register_blockdriver` and implements the corresponding
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high-level interface (`read`, `write`, `close`, etc.).
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implements the interface. This *upper half* calls into
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the *lower half* via callbacks.
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* A "lower half" which is typically hardware-specific. This is
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usually implemented at the architecture or board level.
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Subdirectories of ``nuttx/drivers``
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===================================
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* ``1wire/`` :doc:`character/1wire`
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1wire device drivers.
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* ``analog/`` :doc:`character/analog/index`
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This directory holds implementations of analog device drivers.
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This includes drivers for Analog to Digital Conversion (ADC) as
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well as drivers for Digital to Analog Conversion (DAC).
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* ``audio/`` :doc:`special/audio`
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Audio device drivers.
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* ``bch/`` :doc:`character/bch`
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Contains logic that may be used to convert a block driver into
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a character driver. This is the complementary conversion as that
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performed by loop.c.
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* ``can/`` :doc:`character/can`
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This is the CAN drivers and logic support.
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* ``clk/``:doc:`special/clk`
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Clock management (CLK) device drivers.
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* ``contactless/`` :doc:`character/contactless`
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Contactless devices are related to wireless devices. They are not
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communication devices with other similar peers, but couplers/interfaces
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to contactless cards and tags.
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* ``crypto/`` :doc:`character/crypto/index`
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Contains crypto drivers and support logic, including the
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``/dev/urandom`` device.
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* ``devicetree/`` :doc:`special/devicetree`
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Device Tree support.
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* ``dma/`` :doc:`special/dma`
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DMA drivers support.
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* ``eeprom/`` :doc:`block/eeprom`
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An EEPROM is a form of Memory Technology Device (see ``drivers/mtd``).
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EEPROMs are non-volatile memory like FLASH, but differ in underlying
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memory technology and differ in usage in many respects: They may not
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be organized into blocks (at least from the standpoint of the user)
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and it is not necessary to erase the EEPROM memory before re-writing
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it. In addition, EEPROMs tend to be much smaller than FLASH parts,
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usually only a few kilobytes vs megabytes for FLASH. EEPROM tends to
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be used to retain a small amount of device configuration information;
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FLASH tends to be used for program or massive data storage. For these
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reasons, it may not be convenient to use the more complex MTD
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interface but instead use the simple character interface provided by
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the EEPROM drivers.
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* ``efuse/`` :doc:`character/efuse`
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EFUSE drivers support.
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* ``i2c/`` :doc:`special/i2c`
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I2C drivers and support logic.
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* ``i2s/`` :doc:`character/i2s`
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I2S drivers and support logic.
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* ``input/`` :doc:`character/input/index`
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This directory holds implementations of human input device (HID) drivers.
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This includes such things as mouse, touchscreen, joystick,
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keyboard and keypad drivers.
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Note that USB HID devices are treated differently. These can be found under
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``usbdev/`` or ``usbhost/``.
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* ``ioexpander/`` :doc:`special/ioexpander`
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IO Expander drivers.
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* ``ipcc/`` :doc:`character/ipcc`
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IPCC (Inter Processor Communication Controller) driver.
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* ``lcd/`` :doc:`special/lcd`
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Drivers for parallel and serial LCD and OLED type devices.
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* ``leds/`` :doc:`character/leds/index`
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Various LED-related drivers including discrete as well as PWM- driven LEDs.
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* ``loop/`` :doc:`character/loop`
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Supports the standard loop device that can be used to export a
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file (or character device) as a block device.
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See ``losetup()`` and ``loteardown()`` in ``include/nuttx/fs/fs.h``.
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* ``math/`` :doc:`character/math`
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MATH Acceleration drivers.
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* ``misc/`` :doc:`character/nullzero` :doc:`special/rwbuffer` :doc:`block/ramdisk`
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Various drivers that don't fit elsewhere.
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* ``mmcsd/`` :doc:`special/sdio` :doc:`special/mmcsd`
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Support for MMC/SD block drivers. MMC/SD block drivers based on
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SPI and SDIO/MCI interfaces are supported.
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* ``modem/`` :doc:`character/modem`
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Modem Support.
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* ``motor/`` :doc:`character/motor/index`
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Motor control drivers.
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* ``mtd/`` :doc:`special/mtd`
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Memory Technology Device (MTD) drivers. Some simple drivers for
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memory technologies like FLASH, EEPROM, NVRAM, etc.
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(Note: This is a simple memory interface and should not be
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confused with the "real" MTD developed at infradead.org. This
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logic is unrelated; I just used the name MTD because I am not
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aware of any other common way to refer to this class of devices).
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* ``net/`` :doc:`special/net/index`
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Network interface drivers.
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* ``notes/`` :doc:`character/note`
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Note Driver Support.
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* ``pinctrl/`` :doc:`special/pinctrl`
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Configure and manage pin.
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* ``pipes/`` :doc:`special/pipes`
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FIFO and named pipe drivers.
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Standard interfaces are declared in ``include/unistd.h``
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* ``power/`` :doc:`special/power/index`
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Various drivers related to power management.
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* ``rc/`` :doc:`character/rc`
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Remote Control Device Support.
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* ``regmap/`` :doc:`special/regmap`
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Regmap Subsystems Support.
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* ``reset/`` :doc:`special/reset`
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Reset Driver Support.
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* ``rf/`` :doc:`character/rf`
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RF Device Support.
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* ``rptun/`` :doc:`special/rptun`
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Remote Proc Tunnel Driver Support.
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* ``segger/`` :doc:`special/segger`
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Segger RTT drivers.
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* ``sensors/`` :doc:`special/sensors`
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Drivers for various sensors. A sensor driver differs little from
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other types of drivers other than they are use to provide measurements
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of things in environment like temperature, orientation, acceleration,
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altitude, direction, position, etc.
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DACs might fit this definition of a sensor driver as well since they
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measure and convert voltage levels. DACs, however, are retained in
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the ``analog/`` sub-directory.
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* ``serial/``:doc:`character/serial`
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Front-end character drivers for chip-specific UARTs.
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This provide some TTY-like functionality and are commonly used (but
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not required for) the NuttX system console.
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* ``spi/`` :doc:`special/spi`
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SPI drivers and support logic.
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* ``syslog/`` :doc:`special/syslog`
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System logging devices.
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* ``timers/`` :doc:`character/timers/index`
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Includes support for various timer devices.
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* ``usbdev/`` :doc:`special/usbdev`
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USB device drivers.
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* ``usbhost/`` :doc:`special/usbhost`
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USB host drivers.
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* ``usbmisc/`` :doc:`special/usbmisc`
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USB Miscellaneous drivers.
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* ``usbmonitor/`` :doc:`special/usbmonitor`
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USB Monitor support.
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* ``usrsock/`` :doc:`special/usrsock`
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Usrsock Driver Support.
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* ``video/`` :doc:`special/video`
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Video-related drivers.
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* ``virtio/`` :doc:`special/virtio`
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Virtio Device Support.
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* ``wireless/`` :doc:`special/wireless`
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Drivers for various wireless devices.
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Skeleton Files
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==============
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Skeleton files are "empty" frameworks for NuttX drivers. They are provided to
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give you a good starting point if you want to create a new NuttX driver.
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The following skeleton files are available:
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* ``drivers/lcd/skeleton.c`` Skeleton LCD driver
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* ``drivers/mtd/skeleton.c`` Skeleton memory technology device drivers
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* ``drivers/net/skeleton.c`` Skeleton network/Ethernet drivers
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* ``drivers/usbhost/usbhost_skeleton.c`` Skeleton USB host class driver
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Drivers Early Initialization
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============================
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To initialize drivers early in the boot process, the :c:func:`drivers_early_initialize`
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function is introduced. This is particularly beneficial for certain drivers,
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such as SEGGER SystemView, or others that require initialization before the
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system is fully operational.
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It is important to note that during this early initialization phase,
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system resources are not yet available for use. This includes memory allocation,
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file systems, and any other system resources.
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