My post [Luckfox RV1106 Linux Development Board Review] link:
1. Unboxing and testing
2. SDK acquisition and image compilation
3. GPIO lighting
4. Access the Internet through PC shared network and light up Python in Ubuntu
5. Compile the Buildroot system and test the camera
After testing the Luckfox Pro Max with camera and RKNN image recognition, I plan to experiment with various interfaces of the board according to the evaluation plan. For this evaluation of PWM, I still refer to the PWM article of Luckfox Wiki: https://wiki.luckfox.com/zh/Luckfox-Pico/Luckfox-Pico-PWM .
1. Preparation for PWM evaluation
First look at the PWM pin distribution of the board. The manual indicates that the system defaults to PWM10, which is the GPIO1_C6_d pin.
Figure 6-1 Pro Max board IO distribution
Then, as in my third GPIO review, connect an LED through a breadboard for a breathing light test. The pin (board pin 5) is connected to the LED cathode, and the LED anode is connected in series with a 1k resistor to 3V3 (board pin 36).
The local Win10 system still logs in to the development board through ADB and uses the echo command to operate PWM. During the test, I personally felt that the execution order of the test commands written in the manual was a bit messy. After several attempts, the commands are summarized as follows:
// 查看PWM设备
# ls -l /sys/class/pwm
total 0
lrwxrwxrwx 1 root root 0 Jan 1 12:00 pwmchip10 -> ../../devices/platform/ff490020.pwm/pwm/pwmchip10
lrwxrwxrwx 1 root root 0 Jan 1 12:00 pwmchip11 -> ../../devices/platform/ff490030.pwm/pwm/pwmchip11
lrwxrwxrwx 1 root root 0 Jan 1 12:00 pwmchip5 -> ../../devices/platform/ff360010.pwm/pwm/pwmchip5
lrwxrwxrwx 1 root root 0 Jan 1 12:00 pwmchip6 -> ../../devices/platform/ff360020.pwm/pwm/pwmchip6
// 将PWM10_M1(GPIO1_C6_d)导出到用户空间
# echo 0 > /sys/class/pwm/pwmchip10/export
// 查看PWM10单个通道的属性文件（不做上一步导出到用户空间，这条命令会失败）
# ls /sys/class/pwm/pwmchip10/pwm0/
capture enable period power
duty_cycle output_type polarity uevent
// 使能PWM10通道，但是会提示参数错误
# echo 1 > /sys/class/pwm/pwmchip10/pwm0/enable
sh: write error: Invalid argument
// 但是如果先设置PWM周期——这里单位ns，1000000ns即1KHz频率
# echo 1000000 > /sys/class/pwm/pwmchip10/pwm0/period
// 然后再使能PWM10就成功了——必须先使能，不然没有PWM输出
# echo 1 > /sys/class/pwm/pwmchip10/pwm0/enable
// 此时输出最高值LED最亮（LED是低电平点亮），输出0 LED完全熄灭
# echo 1000000 > /sys/class/pwm/pwmchip10/pwm0/duty_cycle
# echo 0 > /sys/class/pwm/pwmchip10/pwm0/duty_cycle
// 设置PWM极性正常
# echo "normal" > /sys/class/pwm/pwmchip10/pwm0/polarity
// 结果发现输出0 LED最亮了，这说明PWM初始是inversed状态
# echo 0 > /sys/class/pwm/pwmchip10/pwm0/duty_cycle
// 设置PWM极性翻转
# echo "inversed" > /sys/class/pwm/pwmchip10/pwm0/polarity
// 果然又恢复输出最高值LED最亮
# echo 1000000 > /sys/class/pwm/pwmchip10/pwm0/duty_cycle
2. C program controls PWM
Still using the C code provided in the document, create the pwm.c source file in the virtual machine, and then compile it using the compilation tool chain provided in the luckfox-pico SDK to get the program file pwm. Next, copy it to the local machine, and then push it to the directory app created by the development board through adb. Finally, give pwm execution permission on the development board, and then run the program to get the breathing light experimental effect.
Figure 6-2 Development board executes PWM program
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
// 定义PWM路径
#define PWM_PATH "/sys/class/pwm/pwmchip10"
// 定义周期（纳秒）
#define PERIOD_NS 1000000
// 定义最小占空比（纳秒）
#define MIN_DUTY_CYCLE_NS 0
// 定义最大占空比（纳秒）
#define MAX_DUTY_CYCLE_NS 1000000
int main() {
// 打开PWM的export文件，准备导出PWM通道
FILE *pwm_export = fopen(PWM_PATH "/export", "w");
if (!pwm_export) {
perror("Failed to open PWM export");
return 1;
}
fprintf(pwm_export, "0"); // 导出第一个PWM通道（索引为0）
fclose(pwm_export);
// 打开PWM通道的周期配置文件，设置周期为PERIOD_NS纳秒
FILE *period_file = fopen(PWM_PATH "/pwm0/period", "w");
if (!period_file) {
perror("Failed to open PWM period");
return 1;
}
fprintf(period_file, "%d", PERIOD_NS);
fclose(period_file);
// 打开PWM通道的使能文件，启用PWM通道
FILE *enable_file = fopen(PWM_PATH "/pwm0/enable", "w");
if (!enable_file) {
perror("Failed to open PWM enable");
return 1;
}
fprintf(enable_file, "1"); // 启用PWM通道
fclose(enable_file);
int direction = 1; // 方向，决定占空比是增加还是减少
int duty_cycle_ns = 0; // 当前占空比，初始值为0
while (1) { // 无限循环，使PWM保持持续输出
duty_cycle_ns += 10000 * direction; // 根据方向增加或减少占空比的值
if(duty_cycle_ns == MAX_DUTY_CYCLE_NS) // 如果达到最大占空比
direction = -1; // 改变方向，从增加变为减少
else if(duty_cycle_ns == MIN_DUTY_CYCLE_NS) // 如果达到最小占空比
direction = 1; // 改变方向，从减少变为增加
// 打开PWM通道的占空比配置文件，设置占空比为duty_cycle_ns纳秒
FILE *duty_cycle_file = fopen(PWM_PATH "/pwm0/duty_cycle", "w");
if (!duty_cycle_file) {
perror("Failed to open PWM duty cycle");
return 1;
}
fprintf(duty_cycle_file, "%d", duty_cycle_ns);
fclose(duty_cycle_file);
usleep(50000); // 暂停50000微秒（即0.05秒）再更新占空比，以实现PWM效果
}
// 最后，别忘了在程序结束前取消导出PWM通道，以释放资源
FILE *pwm_unexport = fopen(PWM_PATH "/unexport", "w");
if (!pwm_unexport) {
perror("Failed to open PWM unexport");
return 1;
}
fprintf(pwm_unexport, "0"); // 取消导出第一个PWM通道（索引为0）
fclose(pwm_unexport);
return 0; // 主函数返回0，表示程序正常结束
}
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