305 lines
8.9 KiB
C
305 lines
8.9 KiB
C
/****************************************************************************
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* drivers/sensors/max31855.c
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*
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****************************************************************************/
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/* Character driver for the Maxim MAX31855 Thermocouple-to-Digital Converter
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*
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* NOTE: Some Maxim MAX31855 chips have an issue it report value 25% lower
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* of real temperature, for more info read this thread:
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* http://www.eevblog.com/forum/projects/max31855-temperature-error/
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*/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/config.h>
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#include <inttypes.h>
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#include <stdlib.h>
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#include <fixedmath.h>
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#include <assert.h>
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#include <errno.h>
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#include <debug.h>
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#include <nuttx/kmalloc.h>
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#include <nuttx/fs/fs.h>
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#include <nuttx/spi/spi.h>
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#include <nuttx/sensors/max31855.h>
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#include <nuttx/random.h>
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#if defined(CONFIG_SPI) && defined(CONFIG_SENSORS_MAX31855)
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/****************************************************************************
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* Pre-processor Definitions
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****************************************************************************/
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/****************************************************************************
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* Private
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****************************************************************************/
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#define MAX31855_FAULT (1 << 16)
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#define MAX31855_SHORT_VCC (1 << 2)
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#define MAX31855_SHORT_GND (1 << 1)
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#define MAX31855_OPEN_CIRCUIT (1 << 0)
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#define MAX31855_TEMP_COUPLE 0xffffc000
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#define MAX31855_TEMP_JUNCTION 0xfff0
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struct max31855_dev_s
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{
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FAR struct spi_dev_s *spi; /* Saved SPI driver instance */
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int16_t temp;
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uint16_t devid; /* Select minor device number */
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};
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/****************************************************************************
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* Private Function Prototypes
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****************************************************************************/
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static void max31855_lock(FAR struct spi_dev_s *spi);
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static void max31855_unlock(FAR struct spi_dev_s *spi);
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/* Character driver methods */
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static ssize_t max31855_read(FAR struct file *filep, FAR char *buffer,
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size_t buflen);
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static ssize_t max31855_write(FAR struct file *filep, FAR const char *buffer,
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size_t buflen);
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/****************************************************************************
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* Private Data
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****************************************************************************/
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static const struct file_operations g_max31855fops =
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{
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NULL, /* open */
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NULL, /* close */
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max31855_read, /* read */
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max31855_write, /* write */
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};
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/****************************************************************************
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* Private Functions
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****************************************************************************/
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/****************************************************************************
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* Name: max31855_lock
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*
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* Description:
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* Lock and configure the SPI bus.
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*
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****************************************************************************/
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static void max31855_lock(FAR struct spi_dev_s *spi)
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{
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SPI_LOCK(spi, true);
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SPI_SETMODE(spi, SPIDEV_MODE0);
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SPI_SETBITS(spi, 8);
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SPI_HWFEATURES(spi, 0);
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SPI_SETFREQUENCY(spi, 400000);
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}
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/****************************************************************************
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* Name: max31855_unlock
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*
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* Description:
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* Unlock the SPI bus.
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*
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****************************************************************************/
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static void max31855_unlock(FAR struct spi_dev_s *spi)
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{
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SPI_LOCK(spi, false);
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}
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/****************************************************************************
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* Name: max31855_read
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****************************************************************************/
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static ssize_t max31855_read(FAR struct file *filep, FAR char *buffer,
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size_t buflen)
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{
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FAR struct inode *inode = filep->f_inode;
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FAR struct max31855_dev_s *priv = inode->i_private;
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FAR uint16_t *temp = (FAR uint16_t *) buffer;
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int ret = 2;
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int32_t regmsb;
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int32_t regval;
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/* Check for issues */
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if (!buffer)
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{
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snerr("ERROR: Buffer is null\n");
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return -EINVAL;
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}
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if (buflen != 2)
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{
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snerr("ERROR: You can't read something other than 16 bits "
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"(2 bytes)\n");
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return -EINVAL;
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}
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/* Enable MAX31855's chip select */
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max31855_lock(priv->spi);
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SPI_SELECT(priv->spi, SPIDEV_TEMPERATURE(priv->devid), true);
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/* Read temperature */
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SPI_RECVBLOCK(priv->spi, ®msb, 4);
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/* Disable MAX31855's chip select */
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SPI_SELECT(priv->spi, SPIDEV_TEMPERATURE(priv->devid), false);
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max31855_unlock(priv->spi);
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/* Detect any errors during SPI transmission */
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if (!(regmsb) || regmsb == -1)
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{
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snerr("ERROR: Data transmission failed on device %d:\n", priv->devid);
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snerr(" One or more MAX31855 pins are not properly connected!\n\n");
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return -EINVAL;
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}
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regval = (regmsb & 0xff000000) >> 24;
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regval |= (regmsb & 0xff0000) >> 8;
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regval |= (regmsb & 0xff00) << 8;
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regval |= (regmsb & 0xff) << 24;
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sninfo("Read from MAX31855 = 0x%08" PRIX32 "\n", regval);
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/* Feed sensor data to entropy pool */
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add_sensor_randomness(regval);
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/* If negative, fix signal bits */
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if (regval & 0x80000000)
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{
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*temp = 0xc000 | (regval >> 18);
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}
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else
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{
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*temp = (regval >> 18);
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}
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/* Detect any fault */
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if (regval & MAX31855_FAULT)
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{
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snerr("ERROR: A fault was detected by MAX31855:\n");
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if (regval & MAX31855_SHORT_VCC)
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{
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snerr(" The thermocouple input is shorted to VCC!\n");
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}
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if (regval & MAX31855_SHORT_GND)
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{
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snerr(" The thermocouple input is shorted to GND!\n");
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}
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if (regval & MAX31855_OPEN_CIRCUIT)
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{
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snerr(" The thermocouple input is not connected!\n");
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}
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return -EINVAL;
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}
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/* Return two bytes, the temperature is fixed point Q12.2, then divide by 4
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* in your application in other to get real temperature in Celsius degrees.
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*/
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return ret;
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}
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/****************************************************************************
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* Name: max31855_write
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****************************************************************************/
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static ssize_t max31855_write(FAR struct file *filep, FAR const char *buffer,
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size_t buflen)
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{
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return -ENOSYS;
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}
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: max31855_register
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*
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* Description:
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* This function will register the max31855 driver as /dev/tempN
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* where N is the minor device number
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*
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* Input Parameters:
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* devpath - The full path to the driver to register. E.g., "/dev/temp0"
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* spi - An instance of the SPI interface to use to communicate with
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* MAX31855
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* devid - Minor device number. E.g., 0, 1, 2, etc.
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*
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* Returned Value:
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* Zero is returned on success. Otherwise, a negated errno value is
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* returned to indicate the nature of the failure.
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*
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****************************************************************************/
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int max31855_register(FAR const char *devpath, FAR struct spi_dev_s *spi,
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uint16_t devid)
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{
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FAR struct max31855_dev_s *priv;
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int ret;
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/* Sanity check */
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DEBUGASSERT(spi != NULL);
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/* Initialize the MAX31855 device structure */
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priv = (FAR struct max31855_dev_s *)
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kmm_malloc(sizeof(struct max31855_dev_s));
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if (priv == NULL)
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{
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snerr("ERROR: Failed to allocate instance\n");
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return -ENOMEM;
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}
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priv->spi = spi;
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priv->temp = 0;
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priv->devid = devid;
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/* Register the character driver */
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ret = register_driver(devpath, &g_max31855fops, 0666, priv);
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if (ret < 0)
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{
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snerr("ERROR: Failed to register driver: %d\n", ret);
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kmm_free(priv);
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}
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return ret;
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}
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#endif /* CONFIG_SPI && CONFIG_SENSORS_MAX31855 */
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