uPWM.h

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#ifndef __RPIPWM
#define __RPIPWM
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <string>
#include <iostream>
#include <math.h>
 
class RPI_PWM
{
public:
    int start(int channel, int frequency, float duty_cycle = 0, int chip = 2)
    {
        chippath = "/sys/class/pwm/pwmchip" + std::to_string(chip);
        pwmpath = chippath + "/pwm" + std::to_string(channel);
        std::string p = chippath + "/export";
        FILE *const fp = fopen(p.c_str(), "w");
        if (NULL == fp)
        {
            std::cerr << "PWM device does not exist. Make sure to add 'dtoverlay=pwm-2chan' to /boot/firmware/config.txt.\n";
            return -1;
        }
        const int r = fprintf(fp, "%d", channel);
        fclose(fp);
        if (r < 0)
            return r;
        usleep(100000); // it takes a while till the PWM subdir is created
        per = (int)1E9 / frequency;
        setPeriod(per);
        setDutyCycle(duty_cycle);
        enable();
        return r;
    }
 
    void stop()
    {
        disable();
    }
 
    ~RPI_PWM()
    {
        disable();
    }
 
    inline int setDutyCycle(float v) const
    {
        const int dc = (int)round((float)per * (v / 100.0));
        const int r = setDutyCycleNS(dc);
        return r;
    }
 
private:
 
    void setPeriod(int ns) const
    {
        writeSYS(pwmpath + "/" + "period", ns);
    }
 
    inline int setDutyCycleNS(int ns) const
    {
        const int r = writeSYS(pwmpath + "/" + "duty_cycle", ns);
        return r;
    }
 
    void enable() const
    {
        writeSYS(pwmpath + "/" + "enable", 1);
    }
 
    void disable() const
    {
        writeSYS(pwmpath + "/" + "enable", 0);
    }
 
    int per = 0;
 
    std::string chippath;
    std::string pwmpath;
 
    inline int writeSYS(std::string filename, int value) const
    {
        FILE *const fp = fopen(filename.c_str(), "w");
        if (NULL == fp)
        {
            return -1;
        }
        const int r = fprintf(fp, "%d", value);
        fclose(fp);
        return r;
    }
};
 
#endif