# PM_SetBackLight*

## Syntax

      #include <nitro/spi.h>

      u32 PM_SetBackLight( PMLCDTarget target, PMBackLightSwitch sw );

      u32 PM_SetBackLightAsync( PMLCDTarget target, PMBackLightSwitch sw, PMCallback callback, void* arg );

## Arguments

target | Screen that is the target of operation.
sw | Backlight switch.
callback | Callback that is called when the command finishes.
arg | Argument that is used when calling the callback.

## Return Values

If `PM_RESULT_SUCCESS`, the command execution has succeeded (for synchronous functions), or the command was successfully sent to the ARM7 processor (for asynchronous functions).

If `PM_INVALID_COMMAND`, the argument that was passed is invalid.

If `PM_RESULT_BUSY`, the SPI was occupied by other processing and unable to process this function.

## Description

Toggles the specified screen's backlight switch.

The target argument is a `PMLCDTarget` enumerator type that can contain either one of the following values.

Value of target | Targeted LCD
--- | ---
`PM_LCD_TOP` | top screen
`PM_LCD_BOTTOM` | bottom screen
`PM_LCD_ALL` | top and bottom screens

The sw argument is a `PMBackLightSwitch` enumerator type value that specifies one of the following values.

Value of sw | Backlight Operation
--- | ---
`PM_BACKLIGHT_OFF` | Turns the backlight OFF.
`PM_BACKLIGHT_ON` | Turns the backlight ON.

This function performs the operation that is specified by sw on the screen that is specified by the target argument.

Before you use this function, initialize the PM library with the `PM_Init` function. The `PM_Init` function has to be called only once. Also, when you call the `OS_Init` function, there is no need to call the `PM_Init` function separately because it is called from within the `OS_Init` function.

This function can be used from an interrupt handler. This function cannot be used in interrupt-prohibited states other than interrupt handlers.

Asynchronous Functions

This function uses PXI to send the command that performs the corresponding operation in the ARM7 processor. The ARM7 side that receives that command is executed by operating the PMIC. Therefore, this function may not operate instantly after you call it. A synchronous function that waits for the operation to finish, as well as an asynchronous function that only sends commands to the ARM7, are provided. Use either of the functions depending on your operational requirements. (The asynchronous function has "Async" appended to the function name.)

When an asynchronous function is called, the specified `callback` is called when processing on the ARM7 side finishes. The callback type `PMCallback` is defined by:

> ``typedef void ( *PMCallback )( u32 result, void* arg )`;`

This callback is called from within the PXI interrupt handler.

The callback's first argument, `result`, indicates the result of the command. This is either `PM_RESULT_SUCCESS` or `PM_RESULT_BUSY`. The second argument in the callback returns the value `arg`.

About `PM_RESULT_BUSY`

The SPI is used for various other processes besides power management. If you call this function while another process is using it, this function sends a command to the ARM7; there, the SPI is determined to be BUSY, and `PM_RESULT_BUSY` is notified to the ARM9 without actually processing this function. Likewise, if you call this function while another PM process is running, that fact is determined on the ARM9 side and this function returns `PM_RESULT_BUSY`. (In this case, the determination is made before notification is sent to the ARM7.)

Accordingly, if you want to make certain that this function will succeed, make it loop until it succeeds as shown below. (This example does not take into account mistakes such as wrong arguments.)

> Example
> `while( PPM_SetBackLight( ... ) != PM_RESULT_SUCCESS )
> {
> }`

When using the `Async` version of this function, you could do this with code similar to the following.

> Example`
> void setResult( u32 result, void* arg )
> {
> if ( arg )
> {
> *(u32*)arg = result;
> }
> }
> while(1)
> {
> volatile u32 result = PM_RESULT_NONE; //A value that will not be returned
> while ( PM_SetBackLightAsync(..., setResult, (void*)&result ) != PM_RESULT_SUCCESS )
> {
> }
> // Some other process
> otherProcess();
> // Wait for completion
> while( result == PM_RESULT_NONE )
> {
> }
> // Exit the loop on success
> if ( result == PM_RESULT_SUCCESS )
> {
> break;
> }
> }`

## Internal Operation

Operates the `PMIC_CTL` value of the PMIC register.

## See Also

`PM_Init`
`PM_GetBackLight`

## Revision History

2008/08/23 Ended the use of `PM_RESULT_ERROR` and elaborated on `PM_RESULT_BUSY`.
2005/07/07 Elaborated on the `PM_RESULT_ERROR` return value.
2005/06/02 Clarified the origin of the call to the callback.
2004/08/04 Initial version.

CONFIDENTIAL