Commit 65fd21c8 authored by Tom Rix's avatar Tom Rix Committed by Wolfgang Denk

LED Add documentation describing the status_led and colour led API.

This document describes the u-boot status LED API.
This allows common u-boot commands to use a board's leds to
provide status for activities like booting and downloading files.
Signed-off-by: default avatarTom Rix <>
parent 7cdf804f
Status LED
This README describes the status LED API.
The API is defined by the include file include/status_led.h
The first step is to define CONFIG_STATUS_LED in the board config file.
If the LED support is only for a single board, define CONFIG_BOARD_SPECIFIC_LED
in the board config file.
At a minimum, these macros must be defined at
If there are multiple status LED's define
Where <n> can a integer 1 through 3.
STATUS_LED_BIT is passed into the __led_* functions to identify which LED is
being acted on. As such, the value choose must be unique with with respect to
the other STATUS_LED_BIT's. Mapping the value to a physical LED is the
reponsiblity of the __led_* function.
STATUS_LED_STATE is the initial state of the LED. It should be set to one of
these values: STATUS_LED_OFF or STATUS_LED_ON.
STATUS_LED_PERIOD is how long is the LED blink period. This usually set to
(CONFIG_SYS_HZ / <N>) where <N> is the frequency of the blink. Typical values
range from 2 to 10.
Some other LED macros
STATUS_LED_BOOT is the LED to light when the board is booting. This must be a
valid STATUS_LED_BIT value.
STATUS_LED_RED is the red LED. It is used signal errors. This must be a valid
STATUS_LED_BIT value. Other similar color LED's are STATUS_LED_YELLOW and
These board must define these functions
__led_init is called once to initialize the LED to STATUS_LED_STATE. One time
start up code should be placed here.
__led_set is called to change the state of the LED.
__led_toggle is called to toggle the current state of the LED.
Colour LED
Colour LED's are at present only used by ARM.
The functions names explain their purpose.
These are weakly defined in lib_arm/board.c to noops. Where applicable, define
these functions in the board specific source.
TBD : Describe older board dependent macros similar to what is done for
TBD : Describe general support via asm/status_led.h
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