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pwm_ppm.ino
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Wed, Apr 16, 00:55

pwm_ppm.ino
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#include <PinChangeInterrupt.h>
#include <ros.h>
#include <std_msgs/Int16MultiArray.h>
#define CHANNEL_NUMBER 6 //number of chanels in DX6i
#define CHANNEL_DEFAULT_VALUE 1500 //default servo value
#define THROTTLE_DEFAULT_VALUE 1100 //default throttle value
#define FRAME_LENGTH 22000 //PPM frame length in microseconds
#define PULSE_LENGTH 300 //pulse length
#define onState 1 //polarity of the pulses: 1 is positive, 0 is negative
#define sigPin 13 //PPM signal output pin on the arduino
/*
* Define pins used to provide RC PWM signal to Arduino
* Pins 8, 9 and 10 are used since they work on both ATMega328 and
* ATMega32u4 board. So this code will work on Uno/Mini/Nano/Micro/Leonardo
* See PinChangeInterrupt documentation for usable pins on other boards
*/
const byte channel_pin[] = {8, 9, 10, 11};
volatile unsigned long rising_start[] = {0, 0, 0, 0};
volatile long channel_length[] = {0, 0, 0, 0};
// store ppm signals
int ppm[CHANNEL_NUMBER];
// ROS environment
ros::NodeHandle nh;
std_msgs::Int16MultiArray pwm_msg;
void controlCallback( const std_msgs::Int16MultiArray& msg)
{
//update first 4 channels in ppm
for (int i = 0; i < 4; ++i)
{
ppm[i] = msg.data[i];
}
}
ros::Publisher pub("chatter", &pwm_msg);
ros::Subscriber<std_msgs::Int16MultiArray> sub("servo_controls", &controlCallback );
void setup()
{
pinMode(channel_pin[0], INPUT);
pinMode(channel_pin[1], INPUT);
pinMode(channel_pin[2], INPUT);
pinMode(channel_pin[3], INPUT);
attachPinChangeInterrupt(digitalPinToPinChangeInterrupt(channel_pin[0]), onRising0, CHANGE);
attachPinChangeInterrupt(digitalPinToPinChangeInterrupt(channel_pin[1]), onRising1, CHANGE);
attachPinChangeInterrupt(digitalPinToPinChangeInterrupt(channel_pin[2]), onRising2, CHANGE);
attachPinChangeInterrupt(digitalPinToPinChangeInterrupt(channel_pin[3]), onRising3, CHANGE);
// PPM generation set up
for(int i=0; i<CHANNEL_NUMBER; i++)
{
ppm[i]= CHANNEL_DEFAULT_VALUE;
}
pinMode(sigPin, OUTPUT);
digitalWrite(sigPin, !onState); //set the PPM signal pin to the default state (off)
noInterrupts();
TCCR1A = 0; // set entire TCCR1 register to 0
TCCR1B = 0;
OCR1A = 100; // compare match register, change this
TCCR1B |= (1 << WGM12); // turn on CTC mode
TCCR1B |= (1 << CS11); // 8 prescaler: 0,5 microseconds at 16mhz
TIMSK1 |= (1 << OCIE1A); // enable timer compare interrupt
interrupts();
//set up ROS
nh.getHardware()->setBaud(250000);
nh.initNode();
//pwm_msg.layout.dim_length = 1;
pwm_msg.layout.dim = (std_msgs::MultiArrayDimension *)
malloc(sizeof(std_msgs::MultiArrayDimension) * 1);
pwm_msg.layout.dim[0].label = "lox";
pwm_msg.layout.dim[0].size = 4;
pwm_msg.layout.dim[0].stride = 4;
pwm_msg.layout.data_offset = 0;
pwm_msg.data = (int *)malloc(sizeof(int)*4);
pwm_msg.data_length = 4;
//initialize pwm_msg channel
for (int i = 0; i < 4; ++i)
{
pwm_msg.data[i] = CHANNEL_DEFAULT_VALUE;
}
nh.advertise(pub);
nh.subscribe(sub);
}
void processPin(byte pin) {
uint8_t trigger = getPinChangeInterruptTrigger(digitalPinToPCINT(channel_pin[pin]));
if(trigger == RISING) {
rising_start[pin] = micros();
} else if(trigger == FALLING) {
channel_length[pin] = micros() - rising_start[pin];
}
}
void onRising0(void) {
processPin(0);
}
void onRising1(void) {
processPin(1);
}
void onRising2(void) {
processPin(2);
}
void onRising3(void) {
processPin(3);
}
byte counter = 0;
void loop()
{
//noInterrupts();
for (int i = 0; i < 4; ++i)
{
pwm_msg.data[i] = channel_length[i];
}
//interrupts();
if (counter > 1)
{
pub.publish( &pwm_msg );
counter = 0;
}
++counter;
nh.spinOnce();
delay(10);
}
ISR(TIMER1_COMPA_vect)
{
static boolean state = true;
TCNT1 = 0;
if (state)
{ //start pulse
digitalWrite(sigPin, onState);
OCR1A = PULSE_LENGTH * 2;
state = false;
}
else
{ //end pulse and calculate when to start the next pulse
static byte cur_chan_numb;
static unsigned int calc_rest;
digitalWrite(sigPin, !onState);
state = true;
if(cur_chan_numb >= CHANNEL_NUMBER)
{
cur_chan_numb = 0;
calc_rest = calc_rest + PULSE_LENGTH;
OCR1A = (FRAME_LENGTH - calc_rest) * 2;
calc_rest = 0;
}
else
{
OCR1A = (ppm[cur_chan_numb] - PULSE_LENGTH) * 2;
calc_rest = calc_rest + ppm[cur_chan_numb];
cur_chan_numb++;
}
}
}

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