max31855.c
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/*
* max31855.c:
* Extend wiringPi with the max31855 SPI Analog to Digital convertor
* Copyright (c) 2012-2013 Gordon Henderson
***********************************************************************
* This file is part of wiringPi:
* https://projects.drogon.net/raspberry-pi/wiringpi/
*
* wiringPi is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* wiringPi is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with wiringPi.
* If not, see <http://www.gnu.org/licenses/>.
***********************************************************************
*/
#include <wiringPi.h>
#include <wiringPiSPI.h>
#include "max31855.h"
/*
* myAnalogRead:
* Return the analog value of the given pin
* Note: The chip really only has one read "channel", but we're faking it
* here so we can read the error registers. Channel 0 will be the data
* channel, and 1 is the error register code.
* Note: Temperature returned is temp in C * 4, so divide result by 4
*********************************************************************************
*/
static int myAnalogRead (struct wiringPiNodeStruct *node, int pin)
{
unsigned int spiData ;
int temp ;
int chan = pin - node->pinBase ;
wiringPiSPIDataRW (node->fd, (unsigned char *)&spiData, 4) ;
if (chan == 0) // Read temp in C
{
spiData >>= 18 ;
temp = spiData & 0x3FFF ; // Bottom 13 bits
if ((spiData & 0x2000) != 0) // Negative
temp = -temp ;
return temp ;
}
else // Return error bits
return spiData & 0x7 ;
}
/*
* max31855Setup:
* Create a new wiringPi device node for an max31855 on the Pi's
* SPI interface.
*********************************************************************************
*/
int max31855Setup (const int pinBase, int spiChannel)
{
struct wiringPiNodeStruct *node ;
if (wiringPiSPISetup (spiChannel, 5000000) < 0) // 5MHz - prob 4 on the Pi
return -1 ;
node = wiringPiNewNode (pinBase, 2) ;
node->fd = spiChannel ;
node->analogRead = myAnalogRead ;
return 0 ;
}