总结
很多博客文章都是说树莓派PWM是按19.2M基频率来算的，今天用逻辑分析仪抓了一下波形后发现频率有问题，然后按测得的频率反推，算出来我这里好像是按54M的时钟频率来的，不清楚是什么情况。我这里的环境是wiringpi=2.52+树莓派4B+Linux raspberrypi 5.10.52-v7l+ #1440 SMP Tue Jul 27 09:55:21 BST armv7l GNU/Linux
PWM 19.2M时钟的原文 /miaoxiong/p/10556072.html
源码
思路就是读取cpu温度的文件，根据不同温度来控制PWM控制风扇转停，这个编译下来跑起来htop看cpu占用一直等于0，对比原来python写的温控风扇2% 3%的cpu占用在跳，没想到差距这么大。
#include <stdio.h>#include <stdlib.h>#include <stdint.h>#include <wiringPi.h>#define FAN_PIN 1// Hz#define PWM_FRQ (200ul)// frq = 54M / PWM_RANG / divisor#define PWM_RANG (100ul)// temperature#define TEMP_PATH "/sys/class/thermal/thermal_zone0/temp"//#define BUFF_MAX_SIZE 32u#if 0#define DBG_LOG(format, ...)do{printf(format, ##__VA_ARGS__ ); }while(0)#else#define DBG_LOG(format, ...)#endifstatic void GetTemperature(int *temp);static int GetDuty(int temp);unsigned int Duty = 0;FILE *pFile = NULL;char buff[BUFF_MAX_SIZE] = {0};float fTemperature = 0;int Temperature = 0;int main(void){DBG_LOG("Raspberry Pi wiringPi PWM test program\n");if (wiringPiSetup() == -1){DBG_LOG("GPIO setup error!\n");exit(2);}pinMode(FAN_PIN, PWM_OUTPUT);pwmSetMode(PWM_MODE_MS);pwmSetRange(PWM_RANG); //base frq 54MpwmSetClock(54000000/PWM_RANG/PWM_FRQ);pwmWrite(FAN_PIN, 0);while (1){GetTemperature(&Temperature);Duty = GetDuty(Temperature);pwmWrite(FAN_PIN, Duty);DBG_LOG("Temp=%d Duty=%d\n", Temperature, Duty);delay(1000*10);}return 0;}static void GetTemperature(int *temp){pFile = fopen(TEMP_PATH, "r");if(pFile == NULL){DBG_LOG("file can't open PATH=%s p=%p\n", TEMP_PATH, pFile);exit(1);}fgets(buff, BUFF_MAX_SIZE, pFile);*temp = (int)(atoi(buff)/1000.0+0.5);fclose(pFile);}static int GetDuty(int temp){if(temp >= 60){return 100;}else if(temp >= 55){return 80;}else if(temp >= 53){return 70;}else if(temp >= 50){return 60;}else if(temp >= 49){return 50;}else{return 0;}}
最后编译一下
gcc -Wall -O -o fan fan.c -lwiringPi
再加个开机启动
sudo nano /etc/rc.local# 在文件exit前加上 fan程序sudo ./path/fan &
这个温度控制不是很好，转转停停的，
