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LED Add documentation describing the status_led and colour led API.

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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: Tom Rix <Tom.Rix@windriver.com>
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Tom Rix 2009-05-15 23:47:12 +02:00 committed by Wolfgang Denk
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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
STATUS_LED_BIT
STATUS_LED_STATE
STATUS_LED_PERIOD
If there are multiple status LED's define
STATUS_LED_BIT<n>
STATUS_LED_STATE<n>
STATUS_LED_PERIOD<n>
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
STATUS_LED_BLUE.
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.
coloured_LED_init
red_LED_on
red_LED_off
green_LED_on
green_LED_off
yellow_LED_on
yellow_LED_off
blue_LED_on
blue_LED_off
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
CONFIG_TQM8xxL.
TBD : Describe general support via asm/status_led.h