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incubator-nuttx/drivers/sensors/max31865.c

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/****************************************************************************
* drivers/sensors/max31865.c
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
/* Character driver for the Maxim MAX31865 Thermocouple-to-Digital Converter
*
* NOTE: Some Maxim MAX31865 chips have an issue it report value 25% lower
* of real temperature, for more info read this thread:
* http://www.eevblog.com/forum/projects/max31865-temperature-error/
*/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <inttypes.h>
#include <stdlib.h>
#include <fixedmath.h>
#include <assert.h>
#include <errno.h>
#include <debug.h>
#include <math.h>
#include <nuttx/kmalloc.h>
#include <nuttx/fs/fs.h>
#include <nuttx/spi/spi.h>
#include <nuttx/sensors/max31865.h>
#include <nuttx/random.h>
#include <sys/endian.h>
#if defined(CONFIG_SPI) && defined(CONFIG_SENSORS_MAX31865)
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/****************************************************************************
* Private
****************************************************************************/
#define MAX31865_CONFIG_REG 0x00
# define MAX31865_BIAS_ON (1 << 7)
# define MAX31865_AUTO_CONVERSION (1 << 6)
# define MAX31865_ONE_SHOT (1 << 5)
# define MAX31865_3WIRE (1 << 4)
# define MAX31865_FAULT_DET_OFFSET (2)
# define MAX31865_FAULT_DET_MASK (3 << MAX31865_FAULT_DET_OFFSET)
# define MAX31865_FAULT_DET_OFF (0 << MAX31865_FAULT_DET_OFFSET)
# define MAX31865_FAULT_DET_AUTO (1 << MAX31865_FAULT_DET_OFFSET)
# define MAX31865_FAULT_DET_1CYCLE (2 << MAX31865_FAULT_DET_OFFSET)
# define MAX31865_FAULT_DET_2CYCLE (3 << MAX31865_FAULT_DET_OFFSET)
# define MAX31865_FAULT_STATUS_CLR (1 << 1)
# define MAX31865_50HZ_FILTER (1 << 0)
#define MAX31865_RTDMSB_REG 0x01
#define MAX31865_RTDLSB_REG 0x02
#define MAX31865_HFAULTMSB_REG 0x03
#define MAX31865_HFAULTLSB_REG 0x04
#define MAX31865_LFAULTMSB_REG 0x05
#define MAX31865_LFAULTLSB_REG 0x06
#define MAX31865_FAULTSTAT_REG 0x07
#define MAX31865_REF_RESISTOR 430
#define MAX31865_WRITE 0x80
#define RTD_A (3.9083e-3)
#define RTD_B (-5.775e-7)
struct max31865_dev_s
{
FAR struct spi_dev_s *spi; /* Saved SPI driver instance */
int16_t temp;
uint16_t devid; /* Select minor device number */
};
/****************************************************************************
* Private Function Prototypes
****************************************************************************/
static void max31865_lock(FAR struct spi_dev_s *spi);
static void max31865_unlock(FAR struct spi_dev_s *spi);
/* Character driver methods */
static int max31865_open(FAR struct file *filep);
static ssize_t max31865_read(FAR struct file *filep, FAR char *buffer,
size_t buflen);
static ssize_t max31865_write(FAR struct file *filep, FAR const char *buffer,
size_t buflen);
/****************************************************************************
* Private Data
****************************************************************************/
static const struct file_operations g_max31865fops =
{
max31865_open, /* open */
NULL, /* close */
max31865_read, /* read */
max31865_write, /* write */
};
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Name: max31865_lock
*
* Description:
* Lock and configure the SPI bus.
*
****************************************************************************/
static void max31865_lock(FAR struct spi_dev_s *spi)
{
SPI_LOCK(spi, true);
SPI_SETMODE(spi, SPIDEV_MODE1);
SPI_SETBITS(spi, 8);
SPI_HWFEATURES(spi, 0);
SPI_SETFREQUENCY(spi, 400000);
}
/****************************************************************************
* Name: max31865_unlock
*
* Description:
* Unlock the SPI bus.
*
****************************************************************************/
static void max31865_unlock(FAR struct spi_dev_s *spi)
{
SPI_LOCK(spi, false);
}
/****************************************************************************
* Name: max31865_open
*
* Description:
* This function is called whenever the MAX31865 device is opened.
*
****************************************************************************/
static int max31865_open(FAR struct file *filep)
{
FAR struct inode *inode = filep->f_inode;
FAR struct max31865_dev_s *priv = inode->i_private;
unsigned char regval;
/* Enable MAX31865's chip select */
max31865_lock(priv->spi);
SPI_SELECT(priv->spi, SPIDEV_TEMPERATURE(priv->devid), true);
regval = MAX31865_WRITE | MAX31865_CONFIG_REG;
SPI_SEND(priv->spi, regval);
regval = MAX31865_50HZ_FILTER | MAX31865_3WIRE | \
MAX31865_AUTO_CONVERSION | MAX31865_BIAS_ON;
SPI_SEND(priv->spi, regval);
/* Disable MAX31865's chip select */
SPI_SELECT(priv->spi, SPIDEV_TEMPERATURE(priv->devid), false);
max31865_unlock(priv->spi);
return OK;
}
/****************************************************************************
* Name: max31865_read
****************************************************************************/
static ssize_t max31865_read(FAR struct file *filep, FAR char *buffer,
size_t buflen)
{
FAR struct inode *inode = filep->f_inode;
FAR struct max31865_dev_s *priv = inode->i_private;
uint8_t regval[8];
float temp;
uint16_t regmsb;
float rt;
/* Check for issues */
if (!buffer)
{
snerr("ERROR: Buffer is null\n");
return -EINVAL;
}
if (buflen != sizeof(float))
{
snerr("ERROR: You can't read something other than 16 bits "
"(2 bytes)\n");
return -EINVAL;
}
/* Enable MAX31865's chip select */
max31865_lock(priv->spi);
SPI_SELECT(priv->spi, SPIDEV_TEMPERATURE(priv->devid), true);
/* Read temperature */
memset(regval, 0, sizeof(regval));
SPI_SEND(priv->spi, MAX31865_CONFIG_REG);
SPI_RECVBLOCK(priv->spi, regval, sizeof(regval));
/* Disable MAX31865's chip select */
SPI_SELECT(priv->spi, SPIDEV_TEMPERATURE(priv->devid), false);
max31865_unlock(priv->spi);
/* Detect any errors during SPI transmission */
if (*regval != (MAX31865_50HZ_FILTER | MAX31865_3WIRE | \
MAX31865_AUTO_CONVERSION | MAX31865_BIAS_ON))
{
snerr("ERROR: Data transmission failed on device %d:\n", priv->devid);
snerr(" One or more MAX31865 pins are not properly connected!\n\n");
return -EINVAL;
}
/* Resistance of the RTD */
regmsb = ((regval[1] << 8) | regval[2]) >> 1;
rt = (float)(regmsb * MAX31865_REF_RESISTOR / 32768.0);
/* T = (-A + sqrt(A^2 - 4*B*(1 - R/R0))) / (2*B) */
temp = (-RTD_A + sqrt(RTD_A * RTD_A - 4 * RTD_B * (1 - rt / 100.0))) \
/ (2 * RTD_B);
*(FAR float *)buffer = temp;
sninfo("MAX31865 ADC: %d, RTD: %.2f, temperature: %.1f\n", \
regmsb, rt, temp);
return sizeof(temp);
}
/****************************************************************************
* Name: max31865_write
****************************************************************************/
static ssize_t max31865_write(FAR struct file *filep, FAR const char *buffer,
size_t buflen)
{
return -ENOSYS;
}
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: max31865_register
*
* Description:
* This function will register the max31865 driver as /dev/tempN
* where N is the minor device number
*
* Input Parameters:
* devpath - The full path to the driver to register. E.g., "/dev/temp0"
* spi - An instance of the SPI interface to use to communicate with
* MAX31865
* devid - Minor device number. E.g., 0, 1, 2, etc.
*
* Returned Value:
* Zero is returned on success. Otherwise, a negated errno value is
* returned to indicate the nature of the failure.
*
****************************************************************************/
int max31865_register(FAR const char *devpath, FAR struct spi_dev_s *spi,
uint16_t devid)
{
FAR struct max31865_dev_s *priv;
int ret;
/* Sanity check */
DEBUGASSERT(spi != NULL);
/* Initialize the MAX31865 device structure */
priv = (FAR struct max31865_dev_s *)
kmm_malloc(sizeof(struct max31865_dev_s));
if (priv == NULL)
{
snerr("ERROR: Failed to allocate instance\n");
return -ENOMEM;
}
priv->spi = spi;
priv->temp = 0;
priv->devid = devid;
/* Register the character driver */
ret = register_driver(devpath, &g_max31865fops, 0666, priv);
if (ret < 0)
{
snerr("ERROR: Failed to register driver: %d\n", ret);
kmm_free(priv);
}
return ret;
}
#endif /* CONFIG_SPI && CONFIG_SENSORS_MAX31865 */
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