Gpio 测试

Autonomous Machines Jetson & Embedded Systems Jetson Orin Nano
1

您好， 我现在用gpio模拟pwm ，这个频率周期最大支持到多少，现在在内核中使用高精度定时器测试，当频率设置为2微秒时，电平失真，并且达不到需要的2微秒

当使用20微秒周期的时候。信号如下图：

image
image1166×874 83.8 KB

3

hello 550399056,

may I know what’s your approach to simulate PWM?
or… could you please share the code snippets for reference?

4 
 34 static enum hrtimer_restart pwm_timer_callback(struct hrtimer *timer) {
 35     timer_cnt++;
 36     if(timer_cnt == high_cnt){
 37          gpio_set_value(ir_pwm.gpioNum, 0);
 38     }
 39     if(timer_cnt == period_cnt){
 40          gpio_set_value(ir_pwm.gpioNum, 1);
 41          timer_cnt = 0;
 42     }
 43     hrtimer_forward(timer, timer->base->get_time(), pwm_period);
 44 //    state = !state;
 45 //    gpio_set_value(ir_pwm.gpioNum, state);
 46 //    hrtimer_forward_now(timer,pwm_period);
 47 
 48     return HRTIMER_RESTART;
 49 }
5

hello 550399056,

please give it a try by using sleep instead of variable counts to set high/low period.

6

sleep 能到精准到微妙级吗

7

there’re msleep, usleep_range…etc, please give it a try.

8

image
image1166×874 92.6 KB

我使用了 usleep_range ，

 36 static int thread_func(void *data) {
 37 
 38         int i, count;
 39         int step = 2;
 40         int period_us = 1000000 / frequency;              // 计算周期（微秒）                          
 41         int duty_cycle = 30;
 42         int high_time_us = period_us * duty_cycle / 100;  // 高电平时间
 43         int low_time_us = period_us - high_time_us;       // 低电平时间
 44 
 45         while (1){
 46                 usleep_range(high_time_us,high_time_us+step);
 47                 gpio_set_value(ir_pwm.gpioNum, 1);
 48                 usleep_range(low_time_us,low_time_us+step);
 49                 gpio_set_value(ir_pwm.gpioNum, 0);
 50         }
 51         return 0;
 52 }

偶尔会出现上面周期不同步的情况。

9

hello 550399056,

since you’re using an application to toggle GPIO state change, is it related to system process scheduling?
please give it a try by using commands to adjust the process priority (i.e. renice) for specific process,
you may further to assign CPUs individually (i.e. taskset) for the test application.

for instance,

  • To modify the priority
    • please note its ranges from -20 (highest priority) to 19 (lowest priority value), and the default is 0.
    • $ sudo renice -20 -p <pid>
  • To specify CPUs
    • here’s example to assign CPU-2 and CPU-3 for executing application.
    • $ taskset -c -p 2,3 <pid>
10

这是个内核线程，怎么指定优先级呢？

我使用下面方法，效果还是一样：

        thread_body = kthread_create(thread_func, NULL, "thread_pwm");
        if((thread_body))
        {   

            thread_body->prio = 1;
            bind_thread_to_cpu(thread_body,1);
            wake_up_process(thread_body);
        }
11

hello 550399056,

may I know the test results by using constant variable, i.e. usleep_range(10, 20);
and… since it’s a range (i.e. 10~20us) for scheduler to pause the code, would you please also check whether high/low is around 10~20us as well?

12

上面我设置的是：

 45         while (1){
 46                 usleep_range(high_time_us,high_time_us+step);
 47                 gpio_set_value(ir_pwm.gpioNum, 1);
 48                 usleep_range(low_time_us,low_time_us+step);
 49                 gpio_set_value(ir_pwm.gpioNum, 0);
 50         }

具体数值如下：

 45         while (1){
 46                 usleep_range(30,32);
 47                 gpio_set_value(ir_pwm.gpioNum, 1);
 48                 usleep_range(70，72);
 49                 gpio_set_value(ir_pwm.gpioNum, 0);
 50         }

最终效果如示波器上显示的方波一样。不稳定

15

hello 550399056,

may I know which L4T release version you’re working with, did you test on Orin Nano developer kit?

16

我们使用的是orin nx，版本：

JetPack 5.1.4
Linux 35.6.0
Linux Kernel 5.10
Ubuntu 20.04 root file system

17

hello 550399056,

just curious, why you don’t use PWM directly. i.e. $ ls -la /sys/class/pwm/pwmchip*
here’s an example to enable pwm0

cd /sys/class/pwm/pwmchip3
echo 0 > export
cd pwm0
echo 100000000 > period    # i.e. 10Hz
echo 5000 > duty_cycle 
echo 1 > enable