nuttx/drivers/sensors/max6675.c

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/****************************************************************************
* drivers/sensors/max6675.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
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*
* http://www.apache.org/licenses/LICENSE-2.0
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*
* 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.
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*
****************************************************************************/
/* * Character driver for the Maxim MAX6675 Thermocouple-to-Digital Converter
*
* NOTE: Some Maxim MAX6675 chips have an issue it report value 25% lower
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* of real temperature, for more info read this thread:
* http://www.eevblog.com/forum/projects/max6675-temperature-error/
*/
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/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <stdlib.h>
#include <fixedmath.h>
#include <assert.h>
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#include <errno.h>
#include <debug.h>
#include <nuttx/kmalloc.h>
#include <nuttx/fs/fs.h>
#include <nuttx/spi/spi.h>
#include <nuttx/sensors/max6675.h>
#include <nuttx/random.h>
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#if defined(CONFIG_SPI) && defined(CONFIG_SENSORS_MAX6675)
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/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/****************************************************************************
* Private
****************************************************************************/
#define MAX6675_THREE_STATE (1 << 0)
#define MAX6675_DEV_ID (1 << 1)
#define MAX6675_OPEN_CIRCUIT (1 << 2)
#define MAX6675_TEMP_COUPLE 0x7ff8
struct max6675_dev_s
{
FAR struct spi_dev_s *spi; /* Saved SPI driver instance */
int16_t temp;
};
/****************************************************************************
* Private Function Prototypes
****************************************************************************/
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static void max6675_lock(FAR struct spi_dev_s *spi);
static void max6675_unlock(FAR struct spi_dev_s *spi);
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/* Character driver methods */
static ssize_t max6675_read(FAR struct file *filep, FAR char *buffer,
size_t buflen);
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static ssize_t max6675_write(FAR struct file *filep, FAR const char *buffer,
size_t buflen);
/****************************************************************************
* Private Data
****************************************************************************/
static const struct file_operations g_max6675fops =
{
NULL, /* open */
NULL, /* close */
max6675_read, /* read */
max6675_write, /* write */
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};
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Name: max6675_lock
*
* Description:
* Lock and configure the SPI bus.
*
****************************************************************************/
static void max6675_lock(FAR struct spi_dev_s *spi)
{
SPI_LOCK(spi, true);
SPI_SETMODE(spi, SPIDEV_MODE0);
SPI_SETBITS(spi, 8);
SPI_HWFEATURES(spi, 0);
SPI_SETFREQUENCY(spi, 4000000);
}
/****************************************************************************
* Name: max6675_unlock
*
* Description:
* Unlock the SPI bus.
*
****************************************************************************/
static void max6675_unlock(FAR struct spi_dev_s *spi)
{
SPI_LOCK(spi, false);
}
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/****************************************************************************
* Name: max6675_read
****************************************************************************/
static ssize_t max6675_read(FAR struct file *filep, FAR char *buffer,
size_t buflen)
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{
FAR struct inode *inode = filep->f_inode;
FAR struct max6675_dev_s *priv = inode->i_private;
FAR uint16_t *temp = (FAR uint16_t *) buffer;
int ret = 2;
int16_t regmsb;
int16_t regval;
/* Check for issues */
if (!buffer)
{
snerr("ERROR: Buffer is null\n");
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return -EINVAL;
}
if (buflen != 2)
{
snerr("ERROR:");
snerr(" You can't read something other than 16 bits (2 bytes)\n");
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return -EINVAL;
}
/* Enable MAX6675's chip select */
max6675_lock(priv->spi);
SPI_SELECT(priv->spi, SPIDEV_TEMPERATURE(0), true);
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/* Read temperature */
SPI_RECVBLOCK(priv->spi, &regmsb, 2);
/* Disable MAX6675's chip select */
SPI_SELECT(priv->spi, SPIDEV_TEMPERATURE(0), false);
max6675_unlock(priv->spi);
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regval = (regmsb & 0xff00) >> 8;
regval |= (regmsb & 0xff) << 8;
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sninfo("Read from MAX6675 = 0x%04X\n", regval);
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/* Verify if the device ID bit is really zero */
if (regval & MAX6675_DEV_ID)
{
snerr("ERROR: The Device ID bit needs to be 0 !\n");
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ret = -EINVAL;
}
/* Detect if termocople input is open */
if (regval & MAX6675_OPEN_CIRCUIT)
{
snerr("ERROR: The thermocouple input is not connected!\n");
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ret = -EINVAL;
}
/* Feed sensor data to entropy pool */
add_sensor_randomness(regval);
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/* Get the temperature */
*temp = (regval & MAX6675_TEMP_COUPLE) >> 3;
/* Return two bytes, the temperature is fixed point Q10.2, then divide by 4
* in your application in order to get real temperature in Celsius degrees.
*/
return ret;
}
/****************************************************************************
* Name: max6675_write
****************************************************************************/
static ssize_t max6675_write(FAR struct file *filep, FAR const char *buffer,
size_t buflen)
{
return -ENOSYS;
}
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: max6675_register
*
* Description:
* Register the MAX6675 character device as 'devpath'
*
* Input Parameters:
* devpath - The full path to the driver to register. E.g., "/dev/temp0"
* spi - An instance of the SPU interface to use to communicate with
* MAX6675.
*
* Returned Value:
* Zero (OK) on success; a negated errno value on failure.
*
****************************************************************************/
int max6675_register(FAR const char *devpath, FAR struct spi_dev_s *spi)
{
FAR struct max6675_dev_s *priv;
int ret;
/* Sanity check */
DEBUGASSERT(spi != NULL);
/* Initialize the MAX6675 device structure */
priv = (FAR struct max6675_dev_s *)
kmm_malloc(sizeof(struct max6675_dev_s));
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if (priv == NULL)
{
snerr("ERROR: Failed to allocate instance\n");
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return -ENOMEM;
}
priv->spi = spi;
priv->temp = 0;
/* Register the character driver */
ret = register_driver(devpath, &g_max6675fops, 0666, priv);
if (ret < 0)
{
snerr("ERROR: Failed to register driver: %d\n", ret);
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kmm_free(priv);
}
return ret;
}
#endif /* CONFIG_SPI && CONFIG_SENSORS_MAX6675 */