DigitalOutput2.cpp

Go to the documentation of this file.

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

#include "../hubolib.h"
#include "../hubocfg.h" // Required for changing default I2C device.

using namespace HuboLib;

/*
Compile and link: 
    g++ DigitalOutput2.cpp -L../ -lhubo -lpthread -lrt -o DigitalOutput2.out
Run:
    sudo ./DigitalOutput2.out
Purpose:
    The setting of digital outputs is done with a slight delay.
    Use Readback_DO_Channels() to check what the hardware outputs are really set to.
    Thus double check the values as requested by calls to Set_DO_Channel() and Set_DO_Channels().
*/

int main(void)
{
    // If required - set the I2C device to work with. The Raspberry Pi uses "/dev/i2c-1" which is default, the Banana Pi uses "/dev/i2c-0"
    #ifdef BPI
        g_I2CConfig.m_sI2CDevice = "/dev/i2c-0";
    #endif

    // Initialize the library once in your program.
    if (!Initialize())
    {
        printf ("Error: Initialize\n");
        return 1;
    }
    
    // Reset all channels.
    printf ("Clearing all channels, then setting channels 1, 2 and 3.\n");
    Set_DO_Channels(0x00);
    usleep(1000000);
    Set_DO_Channels(0x07);

    // Read back the digital output values as requested by the Set_DO_Channel(s) function. 
    // We'd expect a 0x07 as the three lower channels are set.
    unsigned char digitalOutputs = 0;
    Get_DO_Channels(digitalOutputs);
    assert (digitalOutputs == 0x07);
    
    // But infact - the outputs might not yet be set to 0x07 in the hardware 
    // but still show 0x00 for a while.
    unsigned char currentDigitalOutputs = 0;
    do 
    {
        Readback_DO_Channels(currentDigitalOutputs);
        printf ("Hardware outputs are 0x%02X\n", currentDigitalOutputs);
    } while (currentDigitalOutputs != digitalOutputs);
    
    // The answer to this is that setting digital outputs is an asynchronous operation.
    // A value set by a call to Set_DO_Channel() or Set_DO_Channels() gets buffered and transmitted
    // in the next cycle time slot. Until then the hardware might still be showing the former state 
    // of the outputs. 
    // So if you really need to stop your execution until the outputs are set then use 
    // Readback_DO_Channels() to double check until the hardware has switched to the required state.
    
    // Free library resources.
    Uninitialize();
    
    return 0;
}