// Rapsberry Pi: SPI in C - Versione 0.57 - 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/RaspberryPi/spi-c.htm

// Compile:  gcc max146-8.c -std=c99 -o max146-8
// Run as user with R&W right on /dev/spidev0.* (NOT ROOT!)
// vv@vvrpi ~ $ ./max146-8
// Using MAX146 - Read all channel in 16 clocks/conversion  mode

#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)
#define SAMPLES 8

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[SAMPLES];
        uint16_t data;	
        
      	uint8_t rx[SAMPLES * 2 + 1];    	// RX buffer 
      	uint8_t tx[SAMPLES * 2 + 1];            // TX buffer 
       
      	struct spi_ioc_transfer tr = 
      	{	.tx_buf = (unsigned long)tx,         
          	.rx_buf = (unsigned long)rx,        
          	.len = SAMPLES * 2 + 1,             
          	.delay_usecs = 0,
          	.speed_hz = SPI_SPEED,   
          	.bits_per_word = 8,
          	.cs_change = 0,
       	};

       for (int i = 0; i < (SAMPLES * 2 + 1 ); i++) tx[i] = 0;
              
       tx[0]  = (uint8_t)MAX146_CONTROL_BYTE | 0x00;
       tx[2]  = (uint8_t)MAX146_CONTROL_BYTE | 0x40;
       tx[4]  = (uint8_t)MAX146_CONTROL_BYTE | 0x10;
       tx[6]  = (uint8_t)MAX146_CONTROL_BYTE | 0x50;
       tx[8]  = (uint8_t)MAX146_CONTROL_BYTE | 0x20; 
       tx[10] = (uint8_t)MAX146_CONTROL_BYTE | 0x60;  
       tx[12] = (uint8_t)MAX146_CONTROL_BYTE | 0x30; 
       tx[14] = (uint8_t)MAX146_CONTROL_BYTE | 0x70;

       	// 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");
      
        for (int i = 0; i < SAMPLES; i++)
        {    // Adjust bit order from buffer (see datasheet)
             data = rx[2*i + 1];
             data = data << 5;
             data = data | (rx[2*i + 2] >> 3);
             
             // Convert to voltage
             volt[i] = VREF * data / 4096;
       	}
       	
       	printf("Rapsberry Pi: SPI in C - Versione 0.57 - 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("TX buffer: ");
        for (int i = 0; i < (SAMPLES * 2 +1 ); i++) printf("0x%02X ", tx[i] ); 
        printf ("\nRX buffer: ");
        for (int i = 0; i < (SAMPLES * 2 +1 ); i++) printf("0x%02X ", rx[i] );        
        printf ("\n");
        
        for (int i = 0; i < SAMPLES; i++)  
                 printf("\nVoltage to CH%d = %f V", i, volt[i]);
                
        printf("\n\n");                                                           
	close(fd);

	return (0);
}