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HWTIMER Device

Introduction to the Timer

Hardware timers generally have two modes of operation, timer mode and counter mode. No matter which mode is operated, it works by counting the pulse signal counted by the internal counter module. Here are some important concepts of timers.

Timer mode: Counts the internal pulse. Timers are often used as timing clocks for timing detection, timing response, and timing control.

Counter mode: The counter can count up or down. The maximum count value of a 16-bit counter is 65535, and the maximum value of a 32-bit counter is 4 294 967 295.

Counting frequency：Since the input frequency is usually fixed, the time it takes for the counter to reach its desired count number can be calculated from just the given frequency - time = count value / count frequency. For example, if the counting frequency is 1 MHz, the counter counts once every 1 / 1000000 seconds. That is, every 1 microsecond, the counter is incremented by one (or subtracted by one), at this time, the maximum timing capability of the 16-bit counter is 65535 microseconds, or 65.535 milliseconds.

Access Hardware Timer Device

The application accesses the hardware timer device through the I/O device management interface provided by RT-Thread. The related interfaces are as follows:

Function	Description
rt_device_find()	to look up the timer device
rt_device_open()	to open the timer device in read-write mode
rt_device_set_rx_indicate()	to set the timeout callback function
rt_device_control()	to control the timer device, you can set the timing mode (single time /cycle),counting frequency, or stop the timer
rt_device_write()	to set the timeout value of the timer. The timer then starts
rt_device_read()	to get the current value of the timer
rt_device_close()	to turn off the timer device.

Find Timer Device

The application obtains the device handle based on the hardware timer device name, and thus can operate the hardware timer device. The device function is as follows:

rt_device_t rt_device_find(const char* name);

Parameter	Description
name	hardware timer device name
return	——
timer device handle	will return to the corresponding device handle if the corresponding device is found
RT_NULL	No device found

In general, the hardware timer device name registered to the system is timer0, timer1, etc. The usage examples are as follows:

#define HWTIMER_DEV_NAME   "timer0"     /* timer name */
rt_device_t hw_dev;                     /* timer device handle */
/* find timer device */
hw_dev = rt_device_find(HWTIMER_DEV_NAME);

Open Timer Device

With the device handle, the application can open the device. When the device is open, it will detect whether the device has been initialized. If it is not initialized, it will call the initialization interface to initialize the device by default. Open the device with the following function:

rt_err_t rt_device_open(rt_device_t dev, rt_uint16_t oflags);

Parameter	Description
dev	hardware timer device handle
oflags	device open mode, is generally opened in read and write mode, which is to take the value：RT_DEVICE_OFLAG_RDWR
return	——
RT_EOK	device opened successfully
other error code	device fail to open

An example of use is as follows:

#define HWTIMER_DEV_NAME   "timer0"     /* timer name */
rt_device_t hw_dev;                     /* timer device handle */
/* find timer device */
hw_dev = rt_device_find(HWTIMER_DEV_NAME);
/* to open the timer device in read-write mode */
rt_device_open(hw_dev, RT_DEVICE_OFLAG_RDWR);

Set the Timeout Callback Function

Set the timer timeout callback function with the following function - this is the function that will be called when the timer reaches its set count value:

rt_err_t rt_device_set_rx_indicate(rt_device_t dev, rt_err_t (*rx_ind)(rt_device_t dev, rt_size_t size))

Parameter	Description
dev	device handle
rx_ind	timeout callback function, provided by the caller
return	——
RT_EOK	success

An example of use is as follows：

#define HWTIMER_DEV_NAME   "timer0"     /* timer name */
rt_device_t hw_dev;                     /* timer device handle */

/* timer timeout callback function */
static rt_err_t timeout_cb(rt_device_t dev, rt_size_t size)
{
    rt_kprintf("this is hwtimer timeout callback fucntion!\n");
    rt_kprintf("tick is :%d !\n", rt_tick_get());

    return 0;
}

static int hwtimer_sample(int argc, char *argv[])
{
    /* find timer device */
    hw_dev = rt_device_find(HWTIMER_DEV_NAME);
    /* open the device in read and write mode */
    rt_device_open(hw_dev, RT_DEVICE_OFLAG_RDWR);
    /* set the timeout callback function */
    rt_device_set_rx_indicate(hw_dev, timeout_cb);
}

Control the Timer Device

By sending control words, the application can configure the hardware timer device with the following function:

rt_err_t rt_device_control(rt_device_t dev, rt_uint8_t cmd, void* arg);

Parameter	Description
dev	device handle
cmd	command control word
arg	controlled parameter
return	——
RT_EOK	function executed successfully
-RT_ENOSYS	execution failed，dev is null
other error code	execution failed

The command control words available for the hardware timer device are as follows：

Control word	Description
HWTIMER_CTRL_FREQ_SET	set the counting frequency
HWTIMER_CTRL_STOP	stop the timer
HWTIMER_CTRL_INFO_GET	get timer feature information
HWTIMER_CTRL_MODE_SET	set timer mode

Get the timer parameter argument, which is a pointer to the structure struct rt_hwtimer_info, to save the obtained information.

Setting frequency is valid only when the timer hardware and included driver set the counting frequency. Generally, the default frequency of the driving setting can be used.

When setting the timer mode, the parameter argument can take the following values：

HWTIMER_MODE_ONESHOT    /* Single timing */
HWTIMER_MODE_PERIOD     /* Periodic timing */

An example of using the timer count frequency and timing mode is as follows:

#define HWTIMER_DEV_NAME   "timer0"     /* timer name */
rt_device_t hw_dev;                     /* timer device handle */
rt_hwtimer_mode_t mode;                 /* timer mode */
rt_uint32_t freq = 10000;               /* couting frequency */

/* Timer timeout callback function */
static rt_err_t timeout_cb(rt_device_t dev, rt_size_t size)
{
    rt_kprintf("this is hwtimer timeout callback fucntion!\n");
    rt_kprintf("tick is :%d !\n", rt_tick_get());

    return 0;
}

static int hwtimer_sample(int argc, char *argv[])
{
    /* find timer device */
    hw_dev = rt_device_find(HWTIMER_DEV_NAME);
    /* open the device in read and write mode */
    rt_device_open(hw_dev, RT_DEVICE_OFLAG_RDWR);
    /* Set the timeout callback function */
    rt_device_set_rx_indicate(hw_dev, timeout_cb);

    /* Set the counting frequency (1Mhz or the supported minimum counting frequency by default) */
    rt_device_control(hw_dev, HWTIMER_CTRL_FREQ_SET, &freq);
    /* Set the mode to periodic timer */
    mode = HWTIMER_MODE_PERIOD;
    rt_device_control(hw_dev, HWTIMER_CTRL_MODE_SET, &mode);
}

Set the Timer Timeout Value

The timer timeout value can be set by the following function：

rt_size_t rt_device_write(rt_device_t dev, rt_off_t pos, const void* buffer, rt_size_t size);

Parameter	Description
dev	device handle
pos	write data offset, unused now, can set 0 value
buffer	pointer to the timer timeout structure
size	timeout structure size
return	——
The actual size of the written data
0	fail

The prototype of the timeout structure is shown below :

typedef struct rt_hwtimerval
{
    rt_int32_t sec;      /* second */
    rt_int32_t usec;     /* microsecond */
} rt_hwtimerval_t;

An example of using the timer timeout value is as follows:

#define HWTIMER_DEV_NAME   "timer0"     /* timer name */
rt_device_t hw_dev;                     /* timer device handle */
rt_hwtimer_mode_t mode;                 /* timer mode */
rt_hwtimerval_t timeout_s;              /* Timer timeout value */

/* Timer timeout callback function */
static rt_err_t timeout_cb(rt_device_t dev, rt_size_t size)
{
    rt_kprintf("this is hwtimer timeout callback fucntion!\n");
    rt_kprintf("tick is :%d !\n", rt_tick_get());

    return 0;
}

static int hwtimer_sample(int argc, char *argv[])
{
    /* find timer device */
    hw_dev = rt_device_find(HWTIMER_DEV_NAME);
    /* open the device in read-write mode */
    rt_device_open(hw_dev, RT_DEVICE_OFLAG_RDWR);
    /* set the timeout callback function */
    rt_device_set_rx_indicate(hw_dev, timeout_cb);
    /* set the mode as periodic timer */
    mode = HWTIMER_MODE_PERIOD;
    rt_device_control(hw_dev, HWTIMER_CTRL_MODE_SET, &mode);

    /* Set the timer timeout value to 5s and start the timer */
    timeout_s.sec = 5;      /* second */
    timeout_s.usec = 0;     /* microsecond */
    rt_device_write(hw_dev, 0, &timeout_s, sizeof(timeout_s));
}

Obtain the Current Value of the Timer

The current value of the timer can be obtained by the following function：

rt_size_t rt_device_read(rt_device_t dev, rt_off_t pos, void* buffer, rt_size_t size);

Parameter	Description
dev	timer device handle
pos	write data offset, unused now , can set 0 value
buffer	output parameter, a pointer point to the timeout structure
size	timeout structure size
return	——
Timeout structure size	success
0	fail

An example of use is shown below：

rt_hwtimerval_t timeout_s;      /* Used to save the time the timer has elapsed */
/* Read the elapsed time of the timer  */
rt_device_read(hw_dev, 0, &timeout_s, sizeof(timeout_s));

Close the Timer Device

The timer device can be closed with the following function:

rt_err_t rt_device_close(rt_device_t dev);

Parameter	Description
dev	timer device handle
return	——
RT_EOK	close device successfully
-RT_ERROR	the device has been completely shut down and cannot be closed repeatedly
other error code	fail to close the device

When a timer device has been used and is not necessary anymore, it should be closed, otherwise the device will remain in an open status.