GPIOInputOutput.cpp

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#include <stdio.h>
#include <unistd.h>

#include "../hubolib.h"
#include "../hubocfg.h"

using namespace BCM2835;
using namespace HuboLib;


/*
Compile and link: 
    g++ GPIOInputOutput.cpp -O2 -L../ -lhubo -lpthread -lrt -o GPIOInputOutput.out
Run:
    sudo ./GPIOInputOutput.out
Purpose:
    Configure, read from and write to GPIO pins directly.
*/

int main(void)
{
    // While we do not explicitly need to initialize the GPIO interface we still require to check for a correct initialisation.
    if (!IsGPIOInitialized())
    {
        printf ("The GPIO interface could not be initialised - terminating.\n");
        return -1;
    }
    
    // g_bcm2835Config.m_bUseMutexProtection = false;

    // We will use Broadcom pin 22 which is known as GPIO3 and located on pin header number 15.
    unsigned char pin = 22;
    
    // Configure the pin to be an input.
    FunctionSelectPin (pin, Input);
    
    // Read pin.
    printf ("Input pin %d is set to %d\n", pin, ReadPin(pin));
    
    // We set the pull up resistor on the pin.
    SetPullUpDown (pin, PUD_UP);
    printf ("Input pin %d with pull up is set to %d\n", pin, ReadPin(pin));
    
    // We set the pull down resistor on the pin.
    SetPullUpDown (pin, PUD_DOWN);
    printf ("Input pin %d with pull down is set to %d\n", pin, ReadPin(pin));
    
    // Configure the pin to be an output.
    FunctionSelectPin (pin, Output);

    // Let's set the output and read back it's value.
    WritePin (pin, 0);
    printf ("Cleared output pin %d is set to %d\n", pin, ReadPin(pin));
    WritePin (pin, 1);
    printf ("Set output pin %d is set to %d\n", pin, ReadPin(pin));
    
    
    // Some timing measurements.
    unsigned long long tStart, tStop;
    printf ("\n");

    // Lets see how fast we can write a value.
    tStart = GetTime_MicroSeconds();
    for (int i=0; i<1000000; i++)   
    {
        WritePin (pin, 1);
    }
    tStop = GetTime_MicroSeconds();
    printf ("1000000 samples written in %lluµs - thus %fMHz\n", tStop-tStart, 1000000.0/(tStop-tStart));

    // Lets see how fast we can read a value.
    tStart = GetTime_MicroSeconds();
    for (int i=0; i<1000000; i++)   
    {
        ReadPin (pin);
    }
    tStop = GetTime_MicroSeconds();
    printf ("1000000 samples read in %lluµs - thus %fMHz\n", tStop-tStart, 1000000.0/(tStop-tStart));

    
    // Precision of µsleep() vs. Delay_MicroSeconds().
    unsigned long long delay;
    printf ("\n");
    
    // Compare for short delays.
    delay = 30;
    tStart = GetTime_MicroSeconds();
    usleep (delay);
    tStop = GetTime_MicroSeconds();
    printf ("usleep(%lluµs) took %lluµs\n", delay, tStop-tStart);

    tStart = GetTime_MicroSeconds();
    Delay_MicroSeconds (delay);
    tStop = GetTime_MicroSeconds();
    printf ("Delay_MicroSeconds(%lluµs) took %lluµs\n", delay, tStop-tStart);

    // Compare for long delays.
    delay = 1000000;
    tStart = GetTime_MicroSeconds();
    usleep (delay);
    tStop = GetTime_MicroSeconds();
    printf ("usleep(%lluµs) took %lluµs\n", delay, tStop-tStart);

    tStart = GetTime_MicroSeconds();
    Delay_MicroSeconds (delay);
    tStop = GetTime_MicroSeconds();
    printf ("Delay_MicroSeconds(%lluµs) took %lluµs\n", delay, tStop-tStart);

    // Output of the above.
    /*
    Input pin 22 is set to 0
    Input pin 22 with pull up is set to 1
    Input pin 22 with pull down is set to 0
    Cleared output pin 22 is set to 0
    Set output pin 22 is set to 1

    1000000 samples written in 362509µs - thus 2.758552MHz
    1000000 samples read in 412230µs - thus 2.425830MHz

    usleep(30µs) took 129µs
    Delay_MicroSeconds(30µs) took 41µs
    usleep(1000000µs) took 1000077µs
    Delay_MicroSeconds(1000000µs) took 1000004µs
    */  
    
    // If mutex protection is bypassed (g_bcm2835Config.m_bUseMutexProtection = false;) reading and writing 
    // to the GPIO's further increases in speed.
    /*
    Input pin 22 is set to 0
    Input pin 22 with pull up is set to 1
    Input pin 22 with pull down is set to 0
    Cleared output pin 22 is set to 0
    Set output pin 22 is set to 1

    1000000 samples written in 129636µs - thus 7.713907MHz
    1000000 samples read in 193106µs - thus 5.178503MHz

    usleep(30µs) took 207µs
    Delay_MicroSeconds(30µs) took 39µs
    usleep(1000000µs) took 1000078µs
    Delay_MicroSeconds(1000000µs) took 1000003µs
    */
    
    return 0;
}