UM0851 datasheet(29/245 Pages) STMICROELECTRONICS

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UM0851

Platform section

Doc ID 16604 Rev 2

29/245

/* Clear the match interrupt status

value must be GPT_STATUS_MATCH

void spear_timer_write_status(struct spear_timer *timer, u16 value)

GPT operation

The following APIs can be used to start/stop the GPT timer in single-shot or auto-reload

mode.

/* This shall load the timer with "load" count value and start the timer */

void spear_timer_set_load_start(struct spear_timer *timer, int autoreload, u16

load);

/* These APIs separately load, start and stop the timer */

void spear_timer_set_load(struct spear_timer *timer, int autoreload, u16 load);

void spear_timer_start(struct spear_timer *timer);

void spear_timer_stop(struct spear_timer *timer);

GPT counter value

The 16-bit GPT counter value can be read any time through the following API. Please note

that in case of an asynchronous operation, when the GPT runs on PLL3 and AHB is fed by

PLL1, due to different clock domains, the value reported by this API may not be valid.

Please refer to the GPT application note for more details on this.

/* This shall return the count value of the timer */

unsigned int spear_timer_read_counter(struct spear_timer *timer);

3.1.3

GPT driver usage

Two of these timers are used by the clock keeping and event generation framework of Linux

to maintain Linux time and generation of timer tick. They are defined using the GPT APIs to

configure, program and use the hardware timers. For details please refer to arch/arm/plat-

spear/time.c.

Clock source

One of the GPT timers acts as a free running timer used by Linux to maintain the time of

day. The clock source for Linux is a monotonic increasing timer used by the kernel to get

timer value at any time. For this, it needs to provide a callback to the kernel

(clocksource_read_cycles()) for reading the count value.

static cycle_t clocksource_read_cycles(void)

{

return (cycle_t)spear_timer_read_counter(clk_clksrc_tmr);

}

struct clocksource clocksource_gpt = {

.name

= "clock source",

.rating

= 200,

.read

= clocksource_read_cycles,

.mask

= 0xFFFF,

/* 16 bits */

.mult

= 0,

/* to be computed */

.shift = 20,

.flags

= CLOCK_SOURCE_IS_CONTINUOUS,

};

void hrt_clocksource_init(void)

{

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