DigitalSlaveOutput2.cpp

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#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++ DigitalSlaveOutput2.cpp -L../ -lhubo -lpthread -lrt -o DigitalSlaveOutput2.out
Run:
    sudo ./DigitalSlaveOutput2.out
Purpose:
    The setting of digital outputs (this includes I2C slaves too) is done with a slight delay.
    Use Readback_Slave_DO_Channels() to check what the hardware outputs are really set to.
    Thus double check the values as requested by calls to Set_Slave_DO_Channel() and Set_Slave_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;
    }
    
    int slaveNo = 0; // ... resulting in i2c address 0x21.
    
    // Reset all channels.
    printf ("Clearing all channels on slave %d, then setting channels 1, 2 and 3.\n", slaveNo);
    Set_Slave_DO_Channels(slaveNo, 0x00);
    usleep(1000000);
    Set_Slave_DO_Channels(slaveNo, 0x07);

    // Read back the digital output values as requested by the Set_Slave_DO_Channel(s) function. 
    // We'd expect a 0x07 as the three lower channels are set.
    unsigned char digitalOutputs = 0;
    Get_Slave_DO_Channels(slaveNo, 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_Slave_DO_Channels(slaveNo, currentDigitalOutputs);
        printf ("Hardware outputs of slave %d are 0x%02X\n", slaveNo, 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_Slave_DO_Channel() or Set_Slave_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_Slave_DO_Channels() to double check until the hardware has switched to the required state.
    
    // Free library resources.
    Uninitialize();
    
    return 0;
}