Let me have question about how to use timer interrupt in case of TI AM335X EVM

Hi,

You can find the dmtimer API inside <linux_dir>/arch/arm/plat-omap/include/plat/dmtimer.h and <linux_dir>/arch/arm/plat-omap/dmtimer.c.

You can find a simple kernel module code here: http://e2e.ti.com/support/arm/sitara_arm/f/791/p/270632/1091601.aspx#1091601

Best regards,
Miroslav

HI.

After i checked your link. i just follow same code like below

#include <linux/module.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/clk.h>
#include <linux/irq.h>
#include <linux/interrupt.h>
#include <asm/io.h>
#include <linux/types.h>
#include <plat/dmtimer.h>

static struct omap_dm_timer *timer_ptr;

static int32_t timer_irq;

MODULE_LICENSE("GPL");

static irqreturn_t timer_irq_handler(int irq, void *dev_id)
{
    static int32_t irq_counter = 0;

    omap_dm_timer_write_status(timer_ptr, OMAP_TIMER_INT_OVERFLOW);
    omap_dm_timer_read_status(timer_ptr);

    printk("Meow Meow Meow %d\n", irq_counter++);
    
    return IRQ_HANDLED;
}

static int __init gptimer_test_init(void)
{
    int ret = 0;
    struct clk *gt_fclk;
    uint32_t gt_rate;

    printk("gptimer test : starting module omot\n");
    
    timer_ptr = omap_dm_timer_request();
    if(timer_ptr == NULL)
    {
        printk("gptimer test : NO more gp timers available, bailing out\n");
        return -1;
    }
    printk("before1\n");
    omap_dm_timer_set_source(timer_ptr, OMAP_TIMER_SRC_SYS_CLK);
    printk("before2\n");
    omap_dm_timer_set_prescaler(timer_ptr, 0);
    printk("before3\n");
    timer_irq = omap_dm_timer_get_irq(timer_ptr);
    printk("before4\n");
    ret = request_irq(timer_irq, timer_irq_handler, IRQF_DISABLED | IRQF_TIMER, "gptimer test", timer_irq_handler);
    
    if(ret)
    {
        printk("gptimer test : request failed (on irq %d), bailing out\n", timer_irq);
        return ret;    
    }

    printk("before5\n");
    gt_fclk = omap_dm_timer_get_fclk(timer_ptr);    
    printk("after\n");
    gt_rate = clk_get_rate(gt_fclk);
    printk("after2\n");
    
    omap_dm_timer_set_load(timer_ptr, 1, 0xFFFFFFFF - (3 * gt_rate));
    printk("after3\n");
    omap_dm_timer_start(timer_ptr);
    printk("after4\n");
    return 0;
}

static void __exit gptimer_test_exit(void)
{
    printk("gptimer test: cleanup called\n");
    
    omap_dm_timer_stop(timer_ptr);

    free_irq(timer_irq, timer_irq_handler);

    omap_dm_timer_free(timer_ptr);
}

module_init(gptimer_test_init);
module_exit(gptimer_test_exit);

when i tried "insmod", it has problem.

error message showed "omap_timer omap_timer.0: omap2_dm_timer_set_src: 518: clk_get() sys_ck FAILED"

After i was looking for where the problem from, i found the location in kernel.

it came from "int omap_dm_timer_set_source" function.

int omap_dm_timer_set_source(struct omap_dm_timer *timer, int source)
{
    int ret;
    struct dmtimer_platform_data *pdata;

    if (unlikely(!timer))
        return -EINVAL;

    pdata = timer->pdev->dev.platform_data;
    if (source < 0 || source >= 3)
        return -EINVAL;
    ret = pdata->set_timer_src(timer->pdev, source); // this shows error message when acting.
    return ret;
}

because of it, insmod doesn't work. could you help me what's wrong with my code.

this code is for acting every 3 seconds. actually, i wanna act every 2.5ms.

it's very difficult as a beginner about this programming. also there is few data that i can learn from.

thanks for reading my long writings. i look forward to seeing your anwser again. thank you

Read the manual!

Not all timers are able to use OMAP_TIMER_SRC_SYS_CLK.

Request a specific timer which can switch the clock to OMAP_TIMER_SRC_SYS_CLK.

Or: omit the setting of the clock source, simly using the default clock.

May I ask you why you are not using the hrtimer framework of the linux kernel?

GP timers are hardware timers specific to the AM3xxx.

"hrtimer" ("high resolution timer") is a linux framework. It is available in every linux kernel.

You may use hrtimer if all you want is a simple timer.

You need to use hardware timers if you want to use special hardware features (timer I/O, capture events, etc).

regards

Wolfgang