I got wiringPi to do it through software bit-banging. I might have tried RPIO but my particular application requires that the audio output works, and I understand that RPIO's DMA makes audio go away. I might have also tried wiringPi's softPwm or even softServo, but I also require to run a DC motor through PWM, and I don't want to bring the whole system down to 50Hz just for the servo.
This program worked as a demonstration, has no jitter (because it doesn't continuously drive the positioning pulses), and lands on its target each time with a visibly indistinguishable error. Granted the Pi isn't doing much else at the time to interfere with the program's timing (except running an X server through SSH, gedit, terminal session, everything in top
, etc.).
// Servo trial 11/15/14 by SLC
#include <wiringPi.h>
#include <stdio.h>
#include <unistd.h>
int main()
{
wiringPiSetup();
pinMode( 6, OUTPUT );
digitalWrite( 6, HIGH );
int idx = 0, tries = 0;
while ( tries++ < 30 )
{
int i;
const int period[] = { 500, 1500, 2500 };
printf( "Setting period to %i ms\n", period[idx] );
for ( i = 0; i < 20; ++i )
{
// Output going through an inverter (to convert 3.3V to 5V)
digitalWrite( 6, LOW );
usleep( period[idx] );
digitalWrite( 6, HIGH );
usleep( 20 * 1000 );
}
++idx;
idx %= 3;
sleep( 2 );
}
}
My servo is a Radio Shack Micro Servo, which appears identical to the other "micro" servos out there. I also found I could ditch the inverter and just drive the signal using the 3.3V GPIO.