출처 : http://stackoverflow.com/questions/29369616/beaglebone-black-pwm-using-c

비글보드의 PWM이나 GPIO를 컨트롤 하기 위해서는 특정 파일을 접근하여 조작한다.
아래 예제 소스에서는 내 보드와 파일 이름이 달라(OS 버전별로 조금 다른가보다) 작동하지 않을 수 있지만 일단 프로그래밍 기법 참고용으로 저장한다.
내 보드에 맞는 파일은 예제 소스 아래에 기록한다.

<span class="pun">int trigger_pwm_output(unsigned input_no ) {     FILE *pwm,*duty,*period,*run;``     uint16_t input=0;     uint8_t input_no=0,input_state=0;     unsigned int duty_cycle =500000;     pwm = fopen("/sys/devices/bone_capemgr.9/slots", "w");     fseek(pwm,0,SEEK_SET);     fprintf(pwm,"am33xx_pwm");     fflush(pwm);         switch(input_no)     {         case 0:             fprintf(pwm,"bone_pwm_P8_13");             fflush(pwm);             period = fopen("/sys/devices/ocp.3/pwm_test_P8_13.15/period", "w");             fseek(period,0,SEEK_SET);             fprintf(period,"%d",500000);             fflush(period);                         duty = fopen("/sys/devices/ocp.3/pwm_test_P8_13.15/duty", "w");             fseek(duty,0,SEEK_SET);             run = fopen("/sys/devices/ocp.3/pwm_test_P8_13.15/run", "w");             fseek(run,0,SEEK_SET);             fprintf(run,"%d",0);             fflush(run);                         fseek(run,0,SEEK_SET);             count++;                 do                 {                     duty_cycle += 10;                     fprintf(duty,"%d",duty_cycle);                 }while(count > 0) || (count < 10));             fflush(duty);             fprintf(run,"%d",1);             fflush(run);                         fclose(pwm);             fclose(duty);             fclose(period);             fclose(run);             break;         case 1:             fprintf(pwm,"bone_pwm_P8_19");             fflush(pwm);             period = fopen("/sys/devices/ocp.3/pwm_test_P8_19.16/period", "w");             fseek(period,0,SEEK_SET);             fprintf(period,"%d",500000);             fflush(period);                         duty = fopen("/sys/devices/ocp.3/pwm_test_P8_19.16/duty", "w");             fseek(duty,0,SEEK_SET);             run = fopen("/sys/devices/ocp.3/pwm_test_P8_19.16/run", "w");             fseek(run,0,SEEK_SET);             fprintf(run,"%d",0);             fflush(run);                         fseek(run,0,SEEK_SET);             --count;             do             {                 duty_cycle += 10;                 fprintf(duty,"%d",duty_cycle);             }while(count <10);             fflush(duty);             fprintf(run,"%d",1);             fflush(run);                         fclose(pwm);             fclose(duty);             fclose(period);             fclose(run);             break;     }     return 0; }


내 보드에 맞는 파일 이름 및 PWM 컨트롤 순서
cape 등록 echo cape-universaln > /sys/devices/bone_capemgr.*/slots  
핀설정 조회 config-pin -l P9.16  
PWM 설정 config-pin P9.16 pwm  
 echo pwm > /sys/devices/ocp.*/P9_16_pinmux.*/state  
pinmux 상태 확인 cat /sys/devices/ocp.*/P9_16_pinmux.*/state  
export echo 4 > /sys/class/pwm/export  

export    pin
number, name, pins
 0 EHRPWM0A P9.22,P9.31
 1 EHRPWM0B P9.21,P9.29
 2 ECAPPWM0 P9.42
 3 EHRPWM1A P9.14,P8.36
 4 EHRPWM1B P9.16,P8.34
 5 EHRPWM2A P8.19,P8.45
 6 EHRPWM2B P8.13,P8.46
 7 ECAPPWM2 P9.28
   
 echo 500000 > /sys/class/pwm/pwm4/duty_ns  
 echo 1000000 > /sys/class/pwm/pwm4/period_ns  
 echo 1 > /sys/class/pwm/pwm4/polarity  
 echo 1 > /sys/class/pwm/pwm4/run  
run이 1인 상태에서 polarity 값을 바꿀 수 없다.   

참고사항
cape 해제 : echo -cape번호 > /sys/devices/bone_capemgr.*/slots
부팅시 cape 등록 : uEnv.txt에 적으면 되지 않을까?????