// Rapsberry Pi: SPI in C - Versione 0.56 - Luglio 2013
// Copyright (c) 2013, Vincenzo Villa (https://www.vincenzov.net)
// Creative Commons | Attribuzione-Condividi allo stesso modo 3.0 Unported.
// Creative Commons | Attribution-Share Alike 3.0 Unported
// https://www.vincenzov.net/tutorial/elettronica-di-base/RaspberryPi/spi-c.htm

// Compile:  gcc max146.c -std=c99 -o max146
// Run as user with R&W right on /dev/spidev0.* (NOT ROOT!)
// vv@vvrpi ~ $ ./max146 4 
// Using MAX146 - Read a single voltage

#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 <linux/spi/spidev.h>

#define SPI_SPEED 2000000                       // SPI frequency clock
#define VREF 2.500				// MAX146 voltage reference
#define MAX146_CONTROL_BYTE 0x8F		// 1000 1111 = Unipolar, single ended, external clock (see datasheet)

static const char *device = "/dev/spidev0.0";	// MAX146 CS to RPi CE0
static uint8_t mode = SPI_MODE_0;		// Set SPI mode 

static void exit_on_error (const char *s)	// Exit and print error code
{ 	perror(s);
  	abort();
} 

int main(int argc, char *argv[])
{
	int fd;
	double volt;
        uint16_t data;	
        
      	uint8_t rx[3];    	// RX buffer (3 byte)
      	uint8_t tx[3];          // TX buffer (3 byte)

      	struct spi_ioc_transfer tr = 
      	{	.tx_buf = (unsigned long)tx,         
          	.rx_buf = (unsigned long)rx,        
          	.len = 3,             
          	.delay_usecs = 0,
          	.speed_hz = SPI_SPEED,   
          	.bits_per_word = 8,
          	.cs_change = 0,
       	};

        if (argc != 2) 
        { 
           printf ( "Usage: \n rpi ~ $ ./max146 CH\n CH is channel number, from 0 to 7\n\n");
           exit(-1);        
        }

        switch(argv[1][0])  				// See data sheet
        {
           case '0': tx[0] = MAX146_CONTROL_BYTE | 0x00;  break;
           case '1': tx[0] = MAX146_CONTROL_BYTE | 0x40;  break;
           case '2': tx[0] = MAX146_CONTROL_BYTE | 0x10;  break;
           case '3': tx[0] = MAX146_CONTROL_BYTE | 0x50;  break;
           case '4': tx[0] = MAX146_CONTROL_BYTE | 0x20;  break;
           case '5': tx[0] = MAX146_CONTROL_BYTE | 0x60;  break;
           case '6': tx[0] = MAX146_CONTROL_BYTE | 0x30;  break;
           case '7': tx[0] = MAX146_CONTROL_BYTE | 0x70;  break;
           
           default: printf ( "Usage: \n rpi ~ $ ./max146 CH\n CH is channel number, from 0 to 7\n\n"); exit(-2);
        }   
        
        tx[1]=0;
        tx[2]=0;
                        
       	// Open SPI device
       	if ((fd = open(device, O_RDWR)) < 0) exit_on_error ("Can't open SPI device");

	// Set SPI mode
	if (ioctl(fd, SPI_IOC_WR_MODE, &mode) == -1) exit_on_error ("Can't set SPI mode");

       	// Read data
       	if (ioctl(fd, SPI_IOC_MESSAGE(1), &tr) < 1) exit_on_error ("Can't send SPI message");
                
        // Adjust bit order from buffer (see datasheet)
        data = rx[1];
        data = data << 5;
        data = data | (rx[2] >> 3);
       
       	// Convert to voltage
       	volt = VREF * data / 4096;

       	printf("Rapsberry Pi: SPI in C - Versione 0.56 - Luglio 2013\n");
       	printf("Copyright (c) 2013, Vincenzo Villa (https://www.vincenzov.net)\n");
        printf("Creative Commons | Attribuzione-Condividi allo stesso modo 3.0 Unported.\n");
        printf("Creative Commons | Attribution-Share Alike 3.0 Unported\n");
        printf("https://www.vincenzov.net/tutorial/elettronica-di-base/RaspberryPi/spi-c.htm\n\n");

        printf("Reading data from MAX146 on %s\n\n", device);
        
        printf("Control byte sent to MAX146: 0x%X\n", tx[0]);
        printf("Raw data recived from MAX146: 0x%02X 0x%02X\n\n", rx[1], rx[2] );
        
        printf("Voltage applied to CH%s = %f V\n\n", argv[1], volt);
                                                                   
	close(fd);

	return (0);
}