初次使用RT~Thread，请多指教！

发布于 2011-02-19 23:11:21 浏览：4076 订阅该版

4 个回答

weety 2011-02-23

这家伙很懒，什么也没写！

下面是我驱动at91sam9260的pit代码，你可以参考一下。

```

#define PIT_CPIV(x)	((x) & AT91_PIT_CPIV)
#define PIT_PICNT(x)	(((x) & AT91_PIT_PICNT) >> 20)

static rt_uint32_t pit_cycle;		/* write-once */
static rt_uint32_t pit_cnt;		/* access only w/system irq blocked */

/**
 * This function will handle rtos timer
 */
void rt_timer_handler(int vector)
{
	if (at91_sys_read(AT91_PIT_SR) & AT91_PIT_PITS) {
		unsigned nr_ticks;

/* Get number of ticks performed before irq, and ack it */
		nr_ticks = PIT_PICNT(at91_sys_read(AT91_PIT_PIVR));
		do {
			pit_cnt += pit_cycle;
			rt_tick_increase();
			nr_ticks--;
		} while (nr_ticks);
	}
}

static void at91sam926x_pit_reset(void)
{
	/* Disable timer and irqs */
	at91_sys_write(AT91_PIT_MR, 0);

/* Clear any pending interrupts, wait for PIT to stop counting */
	while (PIT_CPIV(at91_sys_read(AT91_PIT_PIVR)) != 0)
		;

/* Start PIT but don't enable IRQ */
	pit_cnt += pit_cycle * PIT_PICNT(at91_sys_read(AT91_PIT_PIVR));
	at91_sys_write(AT91_PIT_MR, (pit_cycle - 1) | AT91_PIT_PITEN
			| AT91_PIT_PITIEN);
}

/*
 * Set up both clocksource and clockevent support.
 */
static void at91sam926x_pit_init(void)
{
	rt_uint32_t	pit_rate;
	rt_uint32_t	bits;

/*
	 * Use our actual MCK to figure out how many MCK/16 ticks per
	 * 1/HZ period (instead of a compile-time constant LATCH).
	 */
	pit_rate = clk_get_rate(clk_get("mck")) / 16;
	rt_kprintf("pit_rate=%dHZ
", pit_rate);
	pit_cycle = (pit_rate + RT_TICK_PER_SECOND/2) / RT_TICK_PER_SECOND;

/* Initialize and enable the timer */
	at91sam926x_pit_reset();
}

/**
 * This function will init timer0 for system ticks
 */
 void rt_hw_timer_init()
 {
 	at91sam926x_pit_init();

/* install interrupt handler */
	rt_hw_interrupt_install(AT91_ID_SYS, rt_timer_handler, RT_NULL);
	rt_hw_interrupt_umask(AT91_ID_SYS);

}

```