UM0851 datasheet(228/245 Pages) STMICROELECTRONICS

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Power management section

UM0851

228/245

Doc ID 16604 Rev 2

The architecture specific code puts the system into low power mode. The architecture

specific code uses the following algorithm.

●

provides the functions for entering suspend-to-RAM state and then waking-up from

sleep.

●

Each device's driver is asked to suspend the device by putting it into a state compatible

with the target system state.

●

The DDR is put into self-refresh mode. The system enters a low power state,

depending on the mode.

●

Wake-up-enabled devices usually stay partly functional in order to wake the system.

●

The wake-up is normally triggered by a GPIO/Ethernet/RTC interrupt. This trigger

generates the interrupt to wake up the system. The DDR is then moved back from Self

Refresh mode and the system is put back into Normal mode.

●

When the system leaves this low power state, the device's driver is asked to resume.

●

The suspend and resume operations always go together, and both are multi-phase

operations.

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The SPEAr architecture driver (arch/arm/mach-spearxxx/pm.c) registers into the kernel

PM framework using the suspend_set_ops() call. The arch code provides the function

pointers to a set of suspend resume operations to be performed by the SPEAr-specific

code.

The data structure used for the this is:

struct platform_suspend_ops {

int (*valid)(suspend_state_t state);

int (*begin)(suspend_state_t state);

int (*prepare)(void);

int (*enter)(suspend_state_t state);

void (*finish)(void);

void (*end)(void);

}

/*Below is a section of the code demonstrating the registration into the PM framework

from the architecture specific driver */

static int __init spear_pm_init(void) {

…

suspend_pm_ops(&spear_pm_ops);

…

}

/* The device driver which need to act as wakeup source should set up the wakeup

event via following system calls*/

int set_irq_wake(irq, state);

int disable_irq_wake(unsigned int irq)

/* refer drivers/net/arm/spr_eth_syn.c for details */

10.3.2

Clock framework API

The Linux 2.6 kernel provides a clock framework to be used by the drivers in the kernel

space.

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