Programming

Introducing the MSP430 Development Software

We will use three pieces of software during this workshop:

• Notepad++ is a plain text editor, which we will be using to type C code into a file.
• MSPGCC is a C compiler for the Texas Intruments MSP430 family of microcontrollers.
• MSP430Flasher is another piece of software which we will use to transfer a compiled program from the PC to the MSP430 microcontroller where it will be stored in flash memory.

All of this software is completely free, so if you want to continue experimenting with your robot after the workshop you can copy them onto your own PC. If you want to copy them from the PC you’re working on during the workshop, you’ll need a USB key with about 140 MB of space free.

Download the RoboSlam folder

Download the file RoboSlam.zip and extract it somewhere convenient (e.g. on your desktop). This folder contains Notepad++, the MSPGCC C compiler, MSP430Flasher and the build scripts you will need. It’s also where you will store your own programs.

Now you’re ready to begin writing programs for your robot.

Example 1: Blink an LED on and off

This example program is called “Blink” because it blinks the green LED which is connected to pin P2.0 on the MSP430. Begin by creating a new folder called “blink” inside the RoboSlam folder you extracted from the zip file in the previous step. For example, on my PC the folder is “C:\Users\Ted\Desktop\RoboSlam\blink\”.

Now, open Notepad++ which you will use to edit your C code. You will find a shortcut to start Notepad++ in the RoboSlam folder.

Type in (or copy and paste) the code below and save it as a file called “main.c” in your “blink” folder. For example, on my PC this file is “C:\Users\Ted\Desktop\RoboSlam\blink\main.c”.

//
// RoboSlam Example: Blink an LED
// Code is for MSP430G2452 or MSP430G2553
//

#include <msp430.h>

int main( void )
{
    // Stop watchdog timer to prevent time out reset
    WDTCTL = WDTPW + WDTHOLD;
    
    // Set P2.0-2 as outputs and P2.3-7 as inputs
    // Set P1.0-7 as inputs
    P2DIR = 0b00000111;	
    P1DIR = 0b00000000;
    
    // Infinite loop
    while(1)
    {
        P2OUT = 0b00000100;      // LED on - set P2.2 high
        __delay_cycles(1000000); // 1 second delay
        P2OUT = 0b00000000;      // LED off - set P2.2 low
        __delay_cycles(1000000); // 1 second delay
    }
    
    return 0;
}

In the RoboSlam folder, you will find a file called “build_for_g2553.bat”. Copy this file into your “blink” folder.

Connect your Launchpad to the PC using the mini USB cable. Don’t worry if you see a message saying you need Administrator rights to install it – just click “Cancel”.

Once the build file is in your blink folder and the Launchpad is connected, you’re ready to build you program, which means to convert the C code you typed into binary machine code that the microcontroller understands. Double click “build_for_g2553” to start the build process. A command window will open and you’ll see some messages scrolling past. After a few seconds, the new program should be downloaded onto the microcontroller and you should see the LED flashing.

If it doesn’t work right away, or if you see errors appearing on the screen, don’t panic! It’s probably something simple – just ask one of the facilitators to take a quick look.

You are now ready to try out some more complex programs. The following sections provide a series of basic example programs.

Example 2: Controlling the motors

This program repeats the following steps over and over again: drive forward for 2 seconds, turn left for 1 second, drive forward for 2 seconds, turn right for 1 second. This makes the robot drive in a zigzag pattern.

Create a new folder called “motors” (for example, “C:\Users\Ted\Desktop\RoboSlam\motors\”), then type in (or copy and paste) the code below and save it as a file called “main.c” in that folder. You’ll also need to copy the file “build_for_g2553.bat” into the “motors” folder.

//
// RoboSlam Example: Drives around in a square
// Code is for MSP430G2452 or MSP430G2553
//

#include <msp430.h>

int main( void )
{
    // Stop watchdog timer to prevent time out reset
    WDTCTL = WDTPW + WDTHOLD;
    
    // Set P2.0-2 as outputs and P2.3-7 as inputs
    // Set P1.0-7 as inputs
    P2DIR = 0b00000111;	
    P1DIR = 0b00000000;
    
    while(1)
    {
        P2OUT = 0b00000011;      // both motors forwards, LED off
        __delay_cycles(2000000); // 2 second delay
        P2OUT = 0b00000101;      // one motor forwards, one motor stop, LED on
        __delay_cycles(1000000); // 1 second delay
        P2OUT = 0b00000011;      // both motors forwards, LED off
        __delay_cycles(2000000); // 2 second delay
        P2OUT = 0b00000110;      // one motor stop, one motor forwards, LED on
        __delay_cycles(1000000); // 1 second delay
    }
    
    return 0;
}

Example 3: Responding to the colour sensor

This program demonstrates how the voltage – either high (3V) or low (0V) – on a digital input pin is read as 1 or 0 by the program. In this case, the digital input is pin P1.5 which is connected to the infrared colour sensor.

• When the colour sensor is close to a black surface, the output voltage of the sensor is low, so the program reads P1.5 as 0 and sets P2.2 to 0, which turns off the LED.
• When the colour sensor is close to a white surface, the output voltage of the sensor is high, so the program reads P1.5 as 1 and sets P2.2 to 1, which switches on the LED.

Create a folder called “colour” (for example, “C:\Users\Ted\Desktop\RoboSlam\colour\”), then type in (or copy and paste) the code below and save it as a file called “main.c” in that folder. You’ll also need to copy the file “build_for_g2553.bat” into the “colour” folder.

//
// RoboSlam Example: Test colour sensor
// Code is for MSP430G2452 or MSP430G2553
//

#include <msp430.h>

int main( void )
{
    // Stop watchdog timer to prevent time out reset
    WDTCTL = WDTPW + WDTHOLD;
    
    // Set P2.0-2 as outputs and P2.3-7 as inputs
    // Set P1.0-7 as inputs
    P2DIR = 0b00000111;	
    P1DIR = 0b00000000;
    
    while(1)
    {
        // Light LED when white detected
        if (P1IN & BIT5) P2OUT = 0b00000100; // LED on
        else P2OUT = 0b00000000; // LED off
    }
    
    return 0;
}

Example 4: Using the colour sensor to navigate

As in the previous example, this program reads the voltage from the colour sensor as either 1 or 0 on pin P1.5. In this case though, when white is detected (i.e. pin P1.5 = 1) the robot stops and turns until the sensor is back on black before driving forwards again.

Create a folder called “navigate” (for example, “C:\Users\Ted\Desktop\RoboSlam\navigate\”), then type in (or copy and paste) the code below and save it as a file called “main.c” in that folder. You’ll also need to copy the file “build_for_g2553.bat” into the “navigate” folder.

//
// RoboSlam Example: Navigate by ground colour
// Code is for MSP430G2452 or MSP430G2553
//

#include <msp430.h>

int main( void )
{
    // Stop watchdog timer to prevent time out reset
    WDTCTL = WDTPW + WDTHOLD;
    
    // Set P2.0-2 as outputs and P2.3-7 as inputs
    // Set P1.0-7 as inputs
    P2DIR = 0b00000111;	
    P1DIR = 0b00000000;
    
    while(1)
    {
        // Check if white is detected
        if (P1IN & BIT5)
        {
            // turn by running just one motor, LED on
            P2OUT = 0b00000101;
        }
        else
        {
            // both motors on, LED off
            P2OUT = 0b00000011;
        }
    }
    
    return 0;
}

Build Scripts

For reference, these are the same build scripts that are stored in the RoboSlam folder.

Here’s the one for the MSP430G2452, which should be saved as “build_for_g2452.bat” in the same folder as your C program file “main.c”:

@setlocal
@PATH=..\mspgcc-20120406-p20120911\bin\;..\MSP430Flasher_1.2.1\

@REM Compile the C code
msp430-gcc -mmcu=msp430g2452 main.c
@if errorlevel 1 goto end

@REM Convert compiled program to hex format
msp430-objcopy -O ihex a.out a.hex
@if errorlevel 1 goto end

@REM Copy hex file onto microcontroller
msp430flasher -n MSP430G2452 -w a.hex

:end
@pause

Here’s the one for the MSP430G2553, which should be saved as “build_for_g2553.bat” in the same folder as your C program file “main.c”:

@setlocal
@PATH=..\mspgcc-20120406-p20120911\bin\;..\MSP430Flasher_1.2.1\

@REM Compile the C code
msp430-gcc -mmcu=msp430g2553 main.c
@if errorlevel 1 goto end

@REM Convert compiled program to hex format
msp430-objcopy -O ihex a.out a.hex
@if errorlevel 1 goto end

@REM Copy hex file onto microcontroller
msp430flasher -n MSP430G2553 -w a.hex

:end
@pause