LEDs

Numbered LEDs, their /dev/ledN files, and the driver interface. More...

Collaboration diagram for LEDs:

Data Structures
struct	led_ops_t
	Operations an LED driver provides; every one is required. More...
struct	led_t
	An LED: driver operations bound to one device instance. More...
struct	led_table_t
	Every LED in index order; generated in devicetree.c. More...

Driver interface
const led_table_t	dt_led_table
	The board's LEDs; generated in devicetree.c.
void	led_register_node (vfs_node_t *node, const char *path, const led_t *led)
	Register the device file of an LED.

Using LEDs
unsigned	led_count (void)
	Report how many LEDs the board describes.
int	led_set (unsigned index, bool on)
	Turn an LED on or off.
int	led_get (unsigned index, bool *on)
	Read whether an LED is lit.
int	led_toggle (unsigned index)
	Invert an LED.

Detailed Description

Numbered LEDs, their /dev/ledN files, and the driver interface.

Every enabled device whose binding has led: true is an LED. They are numbered in description order, and each registers a device file, by default /dev/ plus its node name, so boards name the nodes led0, led1, and so on. The generated dt_led_table lists them.

Driver	Compatible	Use
GPIO LED	homecore,gpio-led	An LED on a GPIO pin, optionally active-low
Console LED	homecore,console-led	A stand-in for emulators without LEDs: prints each

change on the console |

Device files

Reading a /dev/ledN file returns its state captured at open, 0\n or 1\n, then end of file. Each write sets the LED: 1 or on lights it, 0 or off turns it off, and toggle inverts it. Surrounding whitespace, such as a trailing newline, is ignored; anything else fails with EINVAL. The file accepts O_CREAT, O_TRUNC, and O_APPEND, so fopen(path, "w") works.

write /dev/led0 on
cat /dev/led0

The functions below are for thread context, like the VFS.

See also

LEDs for the Drivers, their configuration, and tests.

Function Documentation

led_count()

unsigned led_count

(

void

)

Report how many LEDs the board describes.

Returns

The number of LEDs; valid indices are 0 to one less.

led_set()

int led_set	(	unsigned	index,
		bool	on
	)

Turn an LED on or off.

Parameters

index	LED number.
on	true to light the LED.

Return values

0	The LED was set.
-1	errno is ENODEV for an index without an LED, or set by the driver.

led_get()

int led_get	(	unsigned	index,
		bool *	on
	)

Read whether an LED is lit.

Parameters

	index	LED number.
[out]	on	true if the LED is lit. Must not be NULL.

Return values

0	on holds the state.
-1	errno is ENODEV for an index without an LED, or set by the driver.

led_toggle()

int led_toggle

(

unsigned

index

)

Invert an LED.

Parameters

index

LED number.

Return values

0	The LED was inverted.
-1	errno as for led_get() and led_set().

led_register_node()

void led_register_node	(	vfs_node_t *	node,
		const char *	path,
		const led_t *	led
	)

Register the device file of an LED.

Called by LED drivers from their init function. Sets up node as a readable and writable device file for led and registers it.

Parameters

node	Node storage owned by the driver instance; must remain valid for the rest of the program.
path	Device file path, such as /dev/led0; must remain valid.
led	The LED; must remain valid for the rest of the program.