// Rapsberry Pi: SPI con wiring Pi - Versione 1.1 - Marzo 2017
// Copyright (c) 2013-2017, Vincenzo Villa
// Creative Commons | Attribuzione - Condividi allo stesso modo 4.0 Internazionale (CC BY-SA 4.0)
// Creative Commons | Attribution-Share Alike 4.0 Unported
// https://www.vincenzov.net/tutorial/RaspberryPi/spi-wpi.htm

#define SPI_SPEED 2000000                       // SPI frequency clock (2 MHz)
#define SPI_CH 0 // SPI channel: 0 or 1
#define VREF 2.500    // MAX146 voltage reference
#define MAX146_CONTROL_BYTE 0x8F  // 1000 1111 = Unipolar, single ended, external clock (see datasheet)
#define MAX146_CH 0 // ADC channel to read: 0...7
#define MAX146_BUFFER_SIZE 3 // Read and write buffer size

#include <stdint.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <getopt.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/types.h>
#include <wiringPi.h>
#include <wiringPiSPI.h>

int main(int argc, char *argv[]) {

    int fd; // Output file for post-analisys
    double volt; // Sample
    uint16_t data;
    uint8_t rtx[MAX146_BUFFER_SIZE]; // RX/TX buffer (3 byte)

    wiringPiSPISetup(SPI_CH, SPI_SPEED); // Set channel and speed

    switch (MAX146_CH) // See data sheet
    {
        case 0: rtx[0] = MAX146_CONTROL_BYTE | 0x00;
            break;
        case 1: rtx[0] = MAX146_CONTROL_BYTE | 0x40;
            break;
        case 2: rtx[0] = MAX146_CONTROL_BYTE | 0x10;
            break;
        case 3: rtx[0] = MAX146_CONTROL_BYTE | 0x50;
            break;
        case 4: rtx[0] = MAX146_CONTROL_BYTE | 0x20;
            break;
        case 5: rtx[0] = MAX146_CONTROL_BYTE | 0x60;
            break;
        case 6: rtx[0] = MAX146_CONTROL_BYTE | 0x30;
            break;
        case 7: rtx[0] = MAX146_CONTROL_BYTE | 0x70;
            break;

        default: printf("Unknow error\n\n");
            exit(-1);
    }

    rtx[1] = 0;
    rtx[2] = 0;

    wiringPiSPIDataRW(SPI_CH, rtx, MAX146_BUFFER_SIZE); // Read fron SPI

    // Adjust bit order from buffer (see datasheet)
    data = rtx[1];
    data = data << 5;
    data = data | (rtx[2] >> 3);

    // Convert to voltage
    volt = VREF * data / 4096;

    printf("Voltage applied to CH%i = %f V\n", MAX146_CH, volt);

    return (0);
}