// Rapsberry Pi: SPI in C - Versione 0.51 - 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 adc.c -std=c99 -o adc
// Run as user with R&W right on /dev/spidev0.* (NOT ROOT!)
// vv@vvrpi ~ $ ./adc 
// Using MAX1240 - Read 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 2100000                       // SPI frequency clock
#define VREF 2.500				// MAX1240 voltag reference

static const char *device = "/dev/spidev0.0";	// MAX1240 CD to RPi CS0
static uint8_t mode = SPI_MODE_0;		// SPI_MODE_0 

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

int main(int argc, char *argv[])
{
	int fd;
	int data;
	double volt;
	
      	uint16_t rx;    	// RX buffer (16 bit unsigned integer)
                        
      	struct spi_ioc_transfer tr = 
      	{	.tx_buf = (unsigned long)NULL,         
          	.rx_buf = (unsigned long)&rx,        
          	.len = 2,             
          	.delay_usecs = 0,
          	.speed_hz = SPI_SPEED,   
          	.bits_per_word = 8,
          	.cs_change = 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 text and data sheet)
        data = ((rx << 5) | (rx >> 11)) & 0xFFF;

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

       	printf("Rapsberry Pi: SPI in C - Versione 0.5 - 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 MAX1240 on %s\n\n", device);
        
        printf("Voltage: %f V - Hex value: 0x%X - Raw value: 0x%X)\n\n", volt, data, rx );
                          
        // Check for timing (see data shet and text)
        if (!(rx & 0x0080) ) printf ("FAIL: EOC in not 1  \n\n");       
                                         
	close(fd);

	return (0);
}