Using the Code::Blocks IDE with SDCC on PIC MCUs

From Code::Blocks

Introduction

I am done with the main items on this, but I may need to expand some sections. Please use this thread for questions. /index.php/topic,8373.msg61848.html

Tim S

This module assumes

  • you, the reader, know a little about programming using C and assembly.
  • you have a Code::Blocks IDE, SDCC, GPUTILS and a PICDEM 2 Plus demo board.
  • The code examples will be using the PIC16F877 and PIC18F452 micro-controllers.

Before getting started,

Getting Started with Simple I/O

We will start with a simple input output program using PORTA and PORTB. Let light some LEDs on the board. We should assign value 0x0A to PORTB. This will light up LEDs at RB3 and RB1. Everytime the switch button at RA4 is pressed, the value will be negated; thus the LEDS will switch between RB3/RB1 and RB2/RB0.

First, start your Code::Blocks IDE. Then use menu "Settings" -> "Compiler and Debugger" to setup the SDCC compiler options.

  1. Select the "SDCC Compiler"
  2. Click on Button "Set as Default"
  3. Click on Tab "Toolchain executables"
  4. Click on Tab "Additional Paths"
  5. Verify the paths for installation and additional directories.
    1. Normal installation directory is "C:\Program Files\SDCC"
    2. Normal additional directories are "C:\Program Files\SDCC\bin" and "C:\Program Files\gputils\bin"
  6. Click on Tab "Search Directories"
  7. Verify the search directories
    1. Normal Compiler search directory of "C:\Program Files\SDCC\include"
    2. PIC Normal Compiler search directory for SDCC 3.0 and later of "C:\Program Files\SDCC\non-free\include"
    3. Normal Linker search directory of "C:\Program Files\SDCC\lib"

Second, create a empty project. In the menu bar, select "File" -> "New" -> "Project". Select "Empty Project" and click on GO. Enter the required information. You will get warning messages that Code::Blocks does not know how to setup somethings; ignore them.

Now change the project so it works with SDCC; In the menu bar, select "Project" -> "Properties"; select the tab "Build Target". Under target options change "Type" to "Native". Note, you need to set all the targets to type "Native". So, select the other target if they exist on the right plane. Set the Project build options; In the menu bar, select "Project" -> "Build Options". Under the "Compiler Settings" Tab and under the tab "Compiler Flag", set either the CPU flag for PIC 16 or 14 bit instructions.

Note: Sometimes it is necessary to use "Compiler Settings" Tab and under the tab "Options" to set the MCU; example is adding "-p18f452" without the double quotes to code for the PIC18F452 MCU.

Once the project is setup, we will create a C file called SimpleIO.c. Add the new file called SimpleIO.c.

Type the following code into the editor. 

#include <pic16/pic18f452.h>

// Configurations
code char at __CONFIG1H conf1 = _OSC_HS_PLL_1H & _OSCS_ON_1H;   // Select HS PLL OSC
code char at __CONFIG2L conf2 = _PUT_ON_2L;
code char at __CONFIG2H conf3 = _WDT_OFF_2H;                    // Disable WDT
code char at __CONFIG4L conf4 = _LVP_OFF_4L;                    // Disable LVP

// Main body
void main() {

    // Initializing ports
    PORTA = 0;
    PORTB = 0;

    // Set RA4 as input and RB3-RB0 as output
    TRISA |= 0x10;
    TRISB &= 0xF0;

    // Set value 0x0A to PORTB
    PORTB = 0x0A;

    // If button is pressed, toggle PORTB
    while(1) {
        if(PORTAbits.RA4 != 0)
            PORTB = ~PORTB;
    }
}

#include <pic/pic16f877.h>

// Configurations
    typedef unsigned int config;
    config at 0x2007 __CONFIG = _HS_OSC & _PWRTE_ON & _BODEN_OFF & _WDT_OFF & _LVP_OFF;

// Main body
void main() {

    // Initializing ports
    PORTA = 0;
    PORTB = 0;

    // Set RA4 as input and RB3-RB0 as output
    TRISA |= 0x10;
    TRISB &= 0xF0;

    // Set value 0x0A to PORTB
    PORTB = 0x0A;

    // If button is pressed, toggle PORTB
    while(1) {
        if(RA4 != 0)
            PORTB = ~PORTB;
    }
}

Hit the save button on the toolbar or from the menu bar, select File → Save. Next, click on Build → Build or Build button at the toolbar at the top. Make sure you have no error or warning at the Output window.

I used the MPLAB to program the demo board. I did it by using "File" -> "Import" of the hex file created by SDCC/gputils. Then, I program the board the way I do under MPLAB.

Now, pressed the switch at RA4 on the demo board a few times. Noticed something wrong? The LEDs do flick, but do not switch between RB3/RB1 and RB2/RB0 all the time. And if you just pressed the switch without releasing it, all the LEDs do light up. This is not something that we want. Let us look at the code again to find out what is the problem. Noticed that in the while loop, as long as RA4 is read 0, value at PORTB will be inverted. With the microcontroller running at 16MHz, a flash push at the switch, which may consume up to 500us, may cause the value in PORTB to invert more than 1000 times. That is why the LEDs appear to be light up in random whenever the switch is pushed. The code has to be modified to detect a push, and a release at the switch.

This program based on code and information from the following

http://en.wikibooks.org/wiki/Embedded_Systems/PIC_Programming

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