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# Power saving support

## Name

Power saving support -- Extensions for saving power

## Overview

There is support in the AT91RM9200 processor HAL for a simple power saving mechanism. This is provided by two functions:

    #include <cyg/hal/hal_intr.h>

    __externC void cyg_hal_at91rm9200_powersave_init( cyg_uint32 ip_addr );

    __externC void cyg_hal_at91rm9200_powerdown( void );

The powersaving system is initialized by calling `cyg_hal_at91rm9200_powersave_init()`. The argument should be the IP address of this machine in network order. This can usually be fetched from the bootp data for an interface after completion of the call to `init_all_network_interfaces()`. e.g. eth0_bootp_data.bp_ciaddr.s_addr.

A call to `cyg_hal_at91rm9200_powerdown()` will put the machine into a low power mode. This will involve switching to a slower system clock speed, disabling all peripherals except those that are defined to cause the system to wake up and return from this function.

## Configuration

The exact behaviour of the power saving system is controlled by the following configuration options:

CYGPKG_HAL_ARM_ARM9_AT91RM9200_POWERSAVE

  This option controls the overall inclusion of the power saving system.

  Default value: on

CYGSEM_HAL_ARM_ARM9_AT91RM9200_POWERSAVE_POLL_ETHERNET

  This option enables polling of the ethernet interface for relevant ARP packets and unicast IP packets. It is necessary for the CPU to run at a higher CPU speed for this option to work.

  Default value: off

CYGSEM_HAL_ARM_ARM9_AT91RM9200_POWERSAVE_IDLE

  If this option is set, the CPU will go into idle mode, which will cause it to halt until an interrupt is delivered.

  Default value: off

CYGVAR_HAL_ARM_ARM9_AT91RM9200_POWERSAVE_ACTIVE_DEVICES

  This option defines the devices that are to be kept running during power down mode. An interrupt from one of these devices is usually the only way of bringing the system out of idle mode. The value of this option is a bit mask with bits set for each device that is to be kept active. The bits correspond to the peripheral identifiers described in the AT91RM9200 documentation.

  Default value: 0x00000000

CYGSEM_HAL_ARM_ARM9_AT91RM9200_POWERSAVE_POLL_GPIO

  This option control whether the power saving system will poll GPIO pins during power saving. For this to work the CPU cannot be put into idle mode.

  Default value: on

CYGVAR_HAL_ARM_ARM9_AT91RM9200_POWERSAVE_PIO_HI

  This is an array of bitmasks of the bits in the PIO PDSR registers. Within the array, index 0 corresponds to PIOA, index 1 to PIOB and so on. For each set bit in these masks, if the value is seen to be 1, then the low power mode will be terminated.

  Default value: 0, 0, 0, 0

CYGVAR_HAL_ARM_ARM9_AT91RM9200_POWERSAVE_PIO_LO

  This is an array of bitmasks of the bits in the PIO PDSR registers. Within the array, index 0 corresponds to PIOA, index 1 to PIOB and so on. For each set bit in these masks, if the value is seen to be 0, then the low power mode will be terminated.

  Default value: 0, 0, 0, 0

CYGVAR_HAL_ARM_ARM9_AT91RM9200_POWERSAVE_PIO_CHANGE

  This is an array of bitmasks of the bits in the PIO PDSR registers. Within the array, index 0 corresponds to PIOA, index 1 to PIOB and so on. For each set bit in these masks, if the value is seen to change between successive polls, then the low power mode will be terminated.

  Default value: 0, 0, 0, 0

CYGBLD_HAL_ARM_ARM9_AT91RM9200_TEST_POWERSAVE

  This option controls whether a simple test is built to exercise power saving support. The test is not built by default as an external means is required to wake the processor up by one of the above configured mechanisms.

  Default value: 0

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