24.8. Device Driver Configuration — RTEMS Classic API Guide 5.4-rc2 (21st August 2026) documentation

# 24.8. Device Driver Configuration

This section describes configuration options related to the device drivers. Note that network device drivers are not covered by the following options.

## 24.8.1. CONFIGURE_APPLICATION_DOES_NOT_NEED_CLOCK_DRIVER

CONSTANT:

  `CONFIGURE_APPLICATION_DOES_NOT_NEED_CLOCK_DRIVER`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then a Clock Driver may be initialized during system initialization.

DESCRIPTION:

  In case this configuration option is defined, then no Clock Driver is initialized during system initialization.

NOTES:

  This configuration parameter is intended to prevent the common user error of using the Hello World example as the baseline for an application and leaving out a clock tick source.

  The application shall define exactly one of the following configuration options

  - CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER,

  - CONFIGURE_APPLICATION_DOES_NOT_NEED_CLOCK_DRIVER, or

  - CONFIGURE_APPLICATION_NEEDS_TIMER_DRIVER,

  otherwise a compile time error in the configuration file will occur.

## 24.8.2. CONFIGURE_APPLICATION_EXTRA_DRIVERS

CONSTANT:

  `CONFIGURE_APPLICATION_EXTRA_DRIVERS`

OPTION TYPE:

  This configuration option is an initializer define.

DEFAULT VALUE:

  The default value is the empty list.

VALUE CONSTRAINTS:

  The value of this configuration option shall be a list of initializers for structures of type `rtems_driver_address_table`.

DESCRIPTION:

  The value of this configuration option is used to initialize the Device Driver Table.

NOTES:

  The value of this configuration option is placed after the entries of other device driver configuration options.

  See CONFIGURE_APPLICATION_PREREQUISITE_DRIVERS for an alternative placement of application device driver initializers.

## 24.8.3. CONFIGURE_APPLICATION_NEEDS_ATA_DRIVER

CONSTANT:

  `CONFIGURE_APPLICATION_NEEDS_ATA_DRIVER`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then the ATA Driver is initialized during system initialization.

NOTES:

  Most BSPs do not include support for an ATA Driver.

  If this option is defined and the BSP does not have this device driver, then the user will get a link time error for an undefined symbol.

## 24.8.4. CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER

CONSTANT:

  `CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then the Clock Driver is initialized during system initialization.

NOTES:

  The Clock Driver is responsible for providing a regular interrupt which invokes a clock tick directive.

  The application shall define exactly one of the following configuration options

  - CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER,

  - CONFIGURE_APPLICATION_DOES_NOT_NEED_CLOCK_DRIVER, or

  - CONFIGURE_APPLICATION_NEEDS_TIMER_DRIVER,

  otherwise a compile time error in the configuration file will occur.

## 24.8.5. CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER

CONSTANT:

  `CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then the Console Driver is initialized during system initialization.

NOTES:

  The Console Driver is responsible for providing the `/dev/console` device file. This device is used to initialize the standard input, output, and error file descriptors.

  BSPs should be constructed in a manner that allows `printk()` to work properly without the need for the Console Driver to be configured.

  The

  - CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER,

  - CONFIGURE_APPLICATION_NEEDS_SIMPLE_CONSOLE_DRIVER, and

  - CONFIGURE_APPLICATION_NEEDS_SIMPLE_TASK_CONSOLE_DRIVER

  configuration options are mutually exclusive.

## 24.8.6. CONFIGURE_APPLICATION_NEEDS_FRAME_BUFFER_DRIVER

CONSTANT:

  `CONFIGURE_APPLICATION_NEEDS_FRAME_BUFFER_DRIVER`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then the Frame Buffer Driver is initialized during system initialization.

NOTES:

  Most BSPs do not include support for a Frame Buffer Driver. This is because many boards do not include the required hardware.

  If this option is defined and the BSP does not have this device driver, then the user will get a link time error for an undefined symbol.

## 24.8.7. CONFIGURE_APPLICATION_NEEDS_IDE_DRIVER

CONSTANT:

  `CONFIGURE_APPLICATION_NEEDS_IDE_DRIVER`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then the IDE Driver is initialized during system initialization.

NOTES:

  Most BSPs do not include support for an IDE Driver.

  If this option is defined and the BSP does not have this device driver, then the user will get a link time error for an undefined symbol.

## 24.8.8. CONFIGURE_APPLICATION_NEEDS_NULL_DRIVER

CONSTANT:

  `CONFIGURE_APPLICATION_NEEDS_NULL_DRIVER`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then the `/dev/null` Driver is initialized during system initialization.

NOTES:

  This device driver is supported by all BSPs.

## 24.8.9. CONFIGURE_APPLICATION_NEEDS_RTC_DRIVER

CONSTANT:

  `CONFIGURE_APPLICATION_NEEDS_RTC_DRIVER`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then the Real-Time Clock Driver is initialized during system initialization.

NOTES:

  Most BSPs do not include support for a real-time clock (RTC). This is because many boards do not include the required hardware.

  If this is defined and the BSP does not have this device driver, then the user will get a link time error for an undefined symbol.

## 24.8.10. CONFIGURE_APPLICATION_NEEDS_SIMPLE_CONSOLE_DRIVER

CONSTANT:

  `CONFIGURE_APPLICATION_NEEDS_SIMPLE_CONSOLE_DRIVER`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then the Simple Console Driver is initialized during system initialization.

NOTES:

  This device driver is responsible for providing the `/dev/console` device file. This device is used to initialize the standard input, output, and error file descriptors.

  This device driver reads via `getchark()`.

  This device driver writes via `rtems_putc()`.

  The Termios framework is not used. There is no support to change device settings, e.g. baud, stop bits, parity, etc.

  The

  - CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER,

  - CONFIGURE_APPLICATION_NEEDS_SIMPLE_CONSOLE_DRIVER, and

  - CONFIGURE_APPLICATION_NEEDS_SIMPLE_TASK_CONSOLE_DRIVER

  configuration options are mutually exclusive.

## 24.8.11. CONFIGURE_APPLICATION_NEEDS_SIMPLE_TASK_CONSOLE_DRIVER

CONSTANT:

  `CONFIGURE_APPLICATION_NEEDS_SIMPLE_TASK_CONSOLE_DRIVER`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then the Simple Task Console Driver is initialized during system initialization.

NOTES:

  This device driver is responsible for providing the `/dev/console` device file. This device is used to initialize the standard input, output, and error file descriptors.

  This device driver reads via `getchark()`.

  This device driver writes into a write buffer. The count of characters written into the write buffer is returned. It might be less than the requested count, in case the write buffer is full. The write is non-blocking and may be called from interrupt context. A dedicated task reads from the write buffer and outputs the characters via `rtems_putc()`. This task runs with the least important priority. The write buffer size is 2047 characters and it is not configurable.

  Use `fsync(STDOUT_FILENO)` or `fdatasync(STDOUT_FILENO)` to drain the write buffer.

  The Termios framework is not used. There is no support to change device settings, e.g. baud, stop bits, parity, etc.

  The

  - CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER,

  - CONFIGURE_APPLICATION_NEEDS_SIMPLE_CONSOLE_DRIVER, and

  - CONFIGURE_APPLICATION_NEEDS_SIMPLE_TASK_CONSOLE_DRIVER

  configuration options are mutually exclusive.

## 24.8.12. CONFIGURE_APPLICATION_NEEDS_STUB_DRIVER

CONSTANT:

  `CONFIGURE_APPLICATION_NEEDS_STUB_DRIVER`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then the Stub Driver is initialized during system initialization.

NOTES:

  This device driver simply provides entry points that return successful and is primarily a test fixture. It is supported by all BSPs.

## 24.8.13. CONFIGURE_APPLICATION_NEEDS_TIMER_DRIVER

CONSTANT:

  `CONFIGURE_APPLICATION_NEEDS_TIMER_DRIVER`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then the Benchmark Timer Driver is initialized during system initialization.

NOTES:

  The Benchmark Timer Driver is intended for the benchmark tests of the RTEMS Testsuite. Applications should not use this driver.

  The application shall define exactly one of the following configuration options

  - CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER,

  - CONFIGURE_APPLICATION_DOES_NOT_NEED_CLOCK_DRIVER, or

  - CONFIGURE_APPLICATION_NEEDS_TIMER_DRIVER,

  otherwise a compile time error will occur.

## 24.8.14. CONFIGURE_APPLICATION_NEEDS_WATCHDOG_DRIVER

CONSTANT:

  `CONFIGURE_APPLICATION_NEEDS_WATCHDOG_DRIVER`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then the Watchdog Driver is initialized during system initialization.

NOTES:

  Most BSPs do not include support for a watchdog device driver. This is because many boards do not include the required hardware.

  If this is defined and the BSP does not have this device driver, then the user will get a link time error for an undefined symbol.

## 24.8.15. CONFIGURE_APPLICATION_NEEDS_ZERO_DRIVER

CONSTANT:

  `CONFIGURE_APPLICATION_NEEDS_ZERO_DRIVER`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then the `/dev/zero` Driver is initialized during system initialization.

NOTES:

  This device driver is supported by all BSPs.

## 24.8.16. CONFIGURE_APPLICATION_PREREQUISITE_DRIVERS

CONSTANT:

  `CONFIGURE_APPLICATION_PREREQUISITE_DRIVERS`

OPTION TYPE:

  This configuration option is an initializer define.

DEFAULT VALUE:

  The default value is the empty list.

VALUE CONSTRAINTS:

  The value of this configuration option shall be a list of initializers for structures of type `rtems_driver_address_table`.

DESCRIPTION:

  The value of this configuration option is used to initialize the Device Driver Table.

NOTES:

  The value of this configuration option is placed after the entries defined by CONFIGURE_BSP_PREREQUISITE_DRIVERS and before all other device driver configuration options.

  See CONFIGURE_APPLICATION_EXTRA_DRIVERS for an alternative placement of application device driver initializers.

## 24.8.17. CONFIGURE_ATA_DRIVER_TASK_PRIORITY

CONSTANT:

  `CONFIGURE_ATA_DRIVER_TASK_PRIORITY`

OPTION TYPE:

  This configuration option is an integer define.

DEFAULT VALUE:

  The default value is 140.

VALUE CONSTRAINTS:

  The value of this configuration option shall be a valid Classic API task priority. The set of valid task priorities is scheduler-specific.

DESCRIPTION:

  The value of this configuration option defines the ATA task priority.

NOTES:

  This configuration option is only evaluated if the configuration option CONFIGURE_APPLICATION_NEEDS_ATA_DRIVER is defined.

## 24.8.18. CONFIGURE_MAXIMUM_DRIVERS

CONSTANT:

  `CONFIGURE_MAXIMUM_DRIVERS`

OPTION TYPE:

  This configuration option is an integer define.

DEFAULT VALUE:

  This is computed by default, and is set to the number of device drivers configured using the `CONFIGURE_APPLICATIONS_NEEDS_XXX_DRIVER` configuration options.

VALUE CONSTRAINTS:

  The value of this configuration option shall satisfy all of the following constraints:

  - It shall be less than or equal to `SIZE_MAX`.

  - It shall be greater than or equal than the number of statically configured device drivers.

  - It shall be less than or equal to a BSP-specific and application-specific value which depends on the size of the memory available to the application.

DESCRIPTION:

  The value of this configuration option defines the number of device drivers.

NOTES:

  If the application will dynamically install device drivers, then this configuration parameter shall be larger than the number of statically configured device drivers. Drivers configured using the `CONFIGURE_APPLICATIONS_NEEDS_XXX_DRIVER` configuration options are statically installed.