PWM examples with multiple architectures

Both of the robot bodies we will provide for the Roboto workshop use servo motors. That means the first task you have in front of you is to set up the PWM with the proper timing for driving servo motors.

My advice is to first use PWM to dim an LED on the board you have chosen. This gives immediate feedback that you have things working.

From there you must implement the following timing:

Period of exactly 20ms
Pulse Widths (the time the pin is high):

1ms moves the servo to its limit in one direction
2ms moves the servo to its limit in the other direction
1.5ms centers the servo motor

In the case of the wheeled robs the 1 and 2 ms widths will move the motors forward or back while the 1.5ms timing will stop the movement.

In the case of the MeARM the settings between 1 and 2ms will position the arm. I suggest writing a function wrapper that can divide up the with into increments of 180 (for positioning in degrees). Moving 1 degree every 15ms results in fairly reliably motion for me.

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Reading from a US-100 Ultrasonic Sensor

Mike Szczys • 11/09/2014 at 19:03 • 0 comments

Reading the US-100 ultrasonic distance sensor is easy:

Make sure the jumper is not in place
Power from 3.3V or 5V to match your logic levels
Pull trigger pin high for 10uS then low
Watch echo pin to go high, measure time before it goes low. This correlates to distance

It would be better to use a hardware timer but this does work. This code example is for the Tiva C Launchpad board.

/*################################################
# Reading US-100 Ultrasonic Sensor using
# the Tiva C Launchpad
#
#
# This example reads from a US-100 ultrasonic sensor
# * Jumper should not be in place
# * VCC to 3.3V
# * GND to GND
# * Trigger to PF2
# * Echo to PF4
#
# It would be much better to use a hardware time
# instead of incrementing "counter" as I've done here
#
# The blue LED is on the same pin as trigger so it
# will flash like crazy
#
# When working correctly the red LED will light up
# when an obstacle is close to the sensor
#
#################################################*/


#include "driverlib/pin_map.h"
#include <stdint.h>
#include <stdbool.h>
#include "inc/hw_gpio.h"
#include "inc/hw_types.h"
#include "inc/hw_memmap.h"
#include "driverlib/sysctl.h"
#include "driverlib/pin_map.h"
#include "driverlib/gpio.h"
#include "driverlib/rom.h"

//Max wait time for reading the sensor:
#define MAX_TIME 7500

void delayMS(int ms) {
    SysCtlDelay( (SysCtlClockGet()/(3*1000))*ms ) ;
}

uint32_t measureD(void) {
    //Pull trigger high
    GPIOPinWrite(GPIO_PORTF_BASE, GPIO_PIN_2, GPIO_PIN_2);
    //wait appropriately
    SysCtlDelay(SysCtlClockGet()/(3*10)) ; //Delay 10uS
    //Pull trigger low
    GPIOPinWrite(GPIO_PORTF_BASE, GPIO_PIN_2, 0);
    //Monitor echo for rising edge
    while (ROM_GPIOPinRead(GPIO_PORTF_BASE, GPIO_PIN_4) == 0) { }
    uint32_t counter = 0;
    
    //loop counter checking for falling edge; MAX_TIME make sure we don't miss it
    while ((ROM_GPIOPinRead(GPIO_PORTF_BASE, GPIO_PIN_4) != 0) && (counter < MAX_TIME)) { counter++; }
    
    //return value
    return counter;
   
}

int main(void)
{
    //Set the clock
    SysCtlClockSet(SYSCTL_SYSDIV_1 | SYSCTL_USE_OSC |   SYSCTL_OSC_MAIN | SYSCTL_XTAL_16MHZ);

    //Enable PortF
    ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);

    //LED Pins as outputs
    ROM_GPIOPinTypeGPIOOutput(GPIO_PORTF_BASE, GPIO_PIN_1 | GPIO_PIN_2 ); //LED on PF1, Trigger on PF2 (there's also an LED there)
    GPIOPinWrite(GPIO_PORTF_BASE, GPIO_PIN_2, 0);
    ROM_GPIOPinTypeGPIOInput(GPIO_PORTF_BASE, GPIO_PIN_4);
    ROM_GPIOPadConfigSet(GPIO_PORTF_BASE, GPIO_PIN_4, GPIO_STRENGTH_2MA, GPIO_PIN_TYPE_STD_WPD);



    while(1)
    {   
        if (measureD() < 750) { GPIOPinWrite(GPIO_PORTF_BASE, GPIO_PIN_1, GPIO_PIN_1); } //LED ON
        else { GPIOPinWrite(GPIO_PORTF_BASE, GPIO_PIN_1, 0); } //LED OFF

        delayMS(20);

    }

}

Atmel SAMD20 Xplained Pro

Mike Szczys • 11/08/2014 at 03:53 • 0 comments

This one's a bit of a kludge but it does work. There's a bit of drift (or something) but I didn't have time to scope the output and fix it. Sorry.

This uses the GCC example for "delay" in the Atmel Software Framework:

http://www.atmel.com/tools/avrsoftwareframework.aspx?tab=overview

There are 3 files you need to edit:

common2/services/delay/example/

/**
 * \file
 *
 * \mainpage
 *
 * \section title Delay service example
 *
 * \section file File(s)
 * - \ref delay_example.c
 *
 * Copyright (c) 2011 - 2014 Atmel Corporation. All rights reserved.
 *
 * \asf_license_start
 *
 * \page License
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * 3. The name of Atmel may not be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 * 4. This software may only be redistributed and used in connection with an
 *    Atmel microcontroller product.
 *
 * THIS SOFTWARE IS PROVIDED BY ATMEL "AS IS" AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT ARE
 * EXPRESSLY AND SPECIFICALLY DISCLAIMED. IN NO EVENT SHALL ATMEL BE LIABLE FOR
 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 * \asf_license_stop
 *
 */
#include <asf.h>

#define PWM_MODULE EXT1_PWM_MODULE
#define PWM_OUT_PIN EXT1_PWM_0_PIN //PB02
#define PWM_OUT_MUX EXT1_PWM_0_MUX

struct tc_module tc_instance;


void configure_tc(void)
{
     struct tc_config config_tc;
     tc_get_config_defaults(&config_tc);
     config_tc.counter_size = TC_COUNTER_SIZE_16BIT;
     config_tc.wave_generation = TC_WAVE_GENERATION_NORMAL_PWM;
     //config_tc.counter_16_bit.compare_capture_channel[0] = (0xFFFF / 2);
     config_tc.counter_32_bit.compare_capture_channel[0] = (8000);
     config_tc.pwm_channel[0].enabled = true;
     config_tc.pwm_channel[0].pin_out = PWM_OUT_PIN;
     config_tc.pwm_channel[0].pin_mux = PWM_OUT_MUX;
     tc_init(&tc_instance, PWM_MODULE, &config_tc);
     tc_set_top_value(&tc_instance,160000);
     tc_enable(&tc_instance);
}

void setDuty(uint32_t duty) {
    tc_set_compare_value(&tc_instance, TC_COMPARE_CAPTURE_CHANNEL_0, duty);
    //Do we need to reset the counter? What if we already passed top?
}

int main(void)
{
	system_init();
	delay_init();

    configure_tc();

	struct port_config pin;
	port_get_config_defaults(&pin);
	pin.direction = PORT_PIN_DIR_OUTPUT;

	port_pin_set_config(LED0_PIN, &pin);
	port_pin_set_output_level(LED0_PIN, LED0_INACTIVE);

	while (true) {

        delay_s(2);
        setDuty(16000);
        
        delay_s(2);
        setDuty(12000);

        delay_s(2);
        setDuty(8000);

	}
}

common2/services/delay/example/samd20_xplained_pro/gcc/asf.h

Just add this before the last #endif:

#include <tc.h>

common2/services/delay/example/samd20_xplained_pro/gcc/config.mk

To this file we're just adding the includes for tc.c and the tc path but I'll paste the entire file:

#
# Copyright (c) 2011 Atmel Corporation. All rights reserved.
#
# \asf_license_start
#
# \page License
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
#
# 1. Redistributions...

Fubarino SD

Mike Szczys • 11/05/2014 at 22:46 • 0 comments

I couldn't find a nice pinout image for the Fubarino SD like I did for the previous 2 boards. If you know of one please leave a comment below.

This board has a silk-screen with the tilde symbol (~) next to some of the pins. I believe these are your options if you are using the Servo library.

The board is programmed using the MPIDE. It's a fork of the Arduino IDE meaning that you can use the Arduino libraries (and code) for this. That makes PWM extremely simple. Here's a servo example:

#include <Servo.h> 
 
//Variable for a Servo object
Servo hobby_servo;
 
// variable to store the servo position
int pos = 0;
 
void setup() 
{ 
  // attaches the servo on pin 7 to the servo object
  hobby_servo.attach(7); 

  // tell servo to go to center position
  hobby_servo.write(90); 
  delay(15);
} 
 
 
void loop() 
{ 
  // tell servo to go to 135 degrees
  hobby_servo.write(135);
  // waits 15ms for the servo to reach the position   
  delay(15);                       

  //Do nothing for 2 seconds
  delay(2000);  

   // tell servo to go to 90 degrees
  hobby_servo.write(90);
  // waits 15ms for the servo to reach the position   
  delay(15);                       

  //Do nothing for 2 seconds
  delay(2000);  
}

Texas Instruments Tiva C Launchpad

Mike Szczys • 11/05/2014 at 16:53 • 1 comment

Use the TivaWare peripheral library to get PWM working on the Tiva C launchpad: http://www.ti.com/tool/sw-tm4c

I made an example of dimming LEDs that can be complied with GCC: https://github.com/szczys/tiva-c-launchpad-hardware-pwm/blob/master/main.c

Specific code for servo timing is found below. The datasheet for the TM4C123GH6PM includes this table which can be used to find out the PWM module, generator, pin, and other values:

/*################################################
# Hardware PWM proof of concept using
# the Tiva C Launchpad
#
# Started with example code by
# lawrence_jeff found here:
# http://forum.stellarisiti.com/topic/707-using-hardware-pwm-on-tiva-launchpad/
# 
# Altered to use code found on section
# 22.3 of the TivaWare Peripheral Driver
# Library User's Guide found here:
# http://www.ti.com/lit/ug/spmu298a/spmu298a.pdf
#
#
# This example drives servo motors on PF1, PF2, and PF3
#
#################################################*/


#include "driverlib/pin_map.h"
#include <stdint.h>
#include <stdbool.h>
#include "inc/hw_gpio.h"
#include "inc/hw_types.h"
#include "inc/hw_memmap.h"
#include "driverlib/sysctl.h"
#include "driverlib/pin_map.h"
#include "driverlib/gpio.h"
#include "driverlib/pwm.h"

void delayMS(int ms) {
    SysCtlDelay( (SysCtlClockGet()/(3*1000))*ms ) ;
}

int
main(void)
{
    uint32_t period = 5000; //20ms (16Mhz / 64pwm_divider / 50)
    uint32_t duty = 250;    //1.5ms pulse width

    //Set the clock
   SysCtlClockSet(SYSCTL_SYSDIV_1 | SYSCTL_USE_OSC |   SYSCTL_OSC_MAIN | SYSCTL_XTAL_16MHZ);

   //Configure PWM Clock divide system clock by 64
   SysCtlPWMClockSet(SYSCTL_PWMDIV_64);

   // Enable the peripherals used by this program.
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);
    SysCtlPeripheralEnable(SYSCTL_PERIPH_PWM1);  //The Tiva Launchpad has two modules (0 and 1). Module 1 covers the LED pins

    //Configure PF1,PF2,PF3 Pins as PWM
    GPIOPinConfigure(GPIO_PF1_M1PWM5);
    GPIOPinConfigure(GPIO_PF2_M1PWM6);
    GPIOPinConfigure(GPIO_PF3_M1PWM7);
    GPIOPinTypePWM(GPIO_PORTF_BASE, GPIO_PIN_1 | GPIO_PIN_2 | GPIO_PIN_3);

    //Configure PWM Options
    //PWM_GEN_2 Covers M1PWM4 and M1PWM5
    //PWM_GEN_3 Covers M1PWM6 and M1PWM7
    PWMGenConfigure(PWM1_BASE, PWM_GEN_2, PWM_GEN_MODE_DOWN | PWM_GEN_MODE_NO_SYNC); 
    PWMGenConfigure(PWM1_BASE, PWM_GEN_3, PWM_GEN_MODE_DOWN | PWM_GEN_MODE_NO_SYNC); 

    //Set the Period (expressed in clock ticks)
    PWMGenPeriodSet(PWM1_BASE, PWM_GEN_2, period);
    PWMGenPeriodSet(PWM1_BASE, PWM_GEN_3, period);

    //Set PWM duty
    PWMPulseWidthSet(PWM1_BASE, PWM_OUT_5,duty);
    PWMPulseWidthSet(PWM1_BASE, PWM_OUT_6,duty);
    PWMPulseWidthSet(PWM1_BASE, PWM_OUT_7,duty);

    // Enable the PWM generator
    PWMGenEnable(PWM1_BASE, PWM_GEN_2);
    PWMGenEnable(PWM1_BASE, PWM_GEN_3);

    // Turn on the Output pins
    PWMOutputState(PWM1_BASE, PWM_OUT_5_BIT | PWM_OUT_6_BIT | PWM_OUT_7_BIT, true);

    while(1)
    {
        delayMS(2000);

        //Drive servo to 135 degrees
        PWMPulseWidthSet(PWM1_BASE, PWM_OUT_5,duty+(duty/2));
        PWMPulseWidthSet(PWM1_BASE, PWM_OUT_6,duty+(duty/2));
        PWMPulseWidthSet(PWM1_BASE, PWM_OUT_7,duty+(duty/2));

        delayMS(2000);

        //Drive servo to 90 degrees
        PWMPulseWidthSet(PWM1_BASE, PWM_OUT_5,duty);
        PWMPulseWidthSet(PWM1_BASE, PWM_OUT_6,duty);
        PWMPulseWidthSet(PWM1_BASE, PWM_OUT_7,duty);

    }

}

Freescale KL25z Freedom Board
Mike Szczys • 11/04/2014 at 22:10 • 0 comments
I used the mbed platform to program PWM on this chip. Links to setup your board for mbed and the mbed pwm api are located here: http://hackaday.io/event/3178/log/10740
You need to use the pins that have PwmOut capability shown in this image:
```
#include "mbed.h"
 
PwmOut servo(PTD4);
 
int main() {
    servo.period_ms(20);
    servo.pulsewidth_ms(2);
    while(1) {
        wait(2);
        servo.pulsewidth_ms(1);
        wait(2);
        servo.pulsewidth_ms(2);
    }
}
```

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PWM examples with multiple architectures

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Reading from a US-100 Ultrasonic Sensor

Atmel SAMD20 Xplained Pro

Fubarino SD

Texas Instruments Tiva C Launchpad

Freescale KL25z Freedom Board

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