/**************************************************************************** * drivers/sensors/max31855.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 MAX31855 Thermocouple-to-Digital Converter * * NOTE: Some Maxim MAX31855 chips have an issue it report value 25% lower * of real temperature, for more info read this thread: * http://www.eevblog.com/forum/projects/max31855-temperature-error/ */ /**************************************************************************** * Included Files ****************************************************************************/ #include #include #include #include #include #include #include #include #include #include #include #include #if defined(CONFIG_SPI) && defined(CONFIG_SENSORS_MAX31855) /**************************************************************************** * Pre-processor Definitions ****************************************************************************/ /**************************************************************************** * Private ****************************************************************************/ #define MAX31855_FAULT (1 << 16) #define MAX31855_SHORT_VCC (1 << 2) #define MAX31855_SHORT_GND (1 << 1) #define MAX31855_OPEN_CIRCUIT (1 << 0) #define MAX31855_TEMP_COUPLE 0xffffc000 #define MAX31855_TEMP_JUNCTION 0xfff0 struct max31855_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 max31855_lock(FAR struct spi_dev_s *spi); static void max31855_unlock(FAR struct spi_dev_s *spi); /* Character driver methods */ static ssize_t max31855_read(FAR struct file *filep, FAR char *buffer, size_t buflen); static ssize_t max31855_write(FAR struct file *filep, FAR const char *buffer, size_t buflen); /**************************************************************************** * Private Data ****************************************************************************/ static const struct file_operations g_max31855fops = { NULL, /* open */ NULL, /* close */ max31855_read, /* read */ max31855_write, /* write */ }; /**************************************************************************** * Private Functions ****************************************************************************/ /**************************************************************************** * Name: max31855_lock * * Description: * Lock and configure the SPI bus. * ****************************************************************************/ static void max31855_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, 400000); } /**************************************************************************** * Name: max31855_unlock * * Description: * Unlock the SPI bus. * ****************************************************************************/ static void max31855_unlock(FAR struct spi_dev_s *spi) { SPI_LOCK(spi, false); } /**************************************************************************** * Name: max31855_read ****************************************************************************/ static ssize_t max31855_read(FAR struct file *filep, FAR char *buffer, size_t buflen) { FAR struct inode *inode = filep->f_inode; FAR struct max31855_dev_s *priv = inode->i_private; FAR uint16_t *temp = (FAR uint16_t *) buffer; int ret = 2; int32_t regmsb; int32_t regval; /* Check for issues */ if (!buffer) { snerr("ERROR: Buffer is null\n"); return -EINVAL; } if (buflen != 2) { snerr("ERROR: You can't read something other than 16 bits " "(2 bytes)\n"); return -EINVAL; } /* Enable MAX31855's chip select */ max31855_lock(priv->spi); SPI_SELECT(priv->spi, SPIDEV_TEMPERATURE(priv->devid), true); /* Read temperature */ SPI_RECVBLOCK(priv->spi, ®msb, 4); /* Disable MAX31855's chip select */ SPI_SELECT(priv->spi, SPIDEV_TEMPERATURE(priv->devid), false); max31855_unlock(priv->spi); /* Detect any errors during SPI transmission */ if (!(regmsb) || regmsb == -1) { snerr("ERROR: Data transmission failed on device %d:\n", priv->devid); snerr(" One or more MAX31855 pins are not properly connected!\n\n"); return -EINVAL; } regval = (regmsb & 0xff000000) >> 24; regval |= (regmsb & 0xff0000) >> 8; regval |= (regmsb & 0xff00) << 8; regval |= (regmsb & 0xff) << 24; sninfo("Read from MAX31855 = 0x%08" PRIX32 "\n", regval); /* Feed sensor data to entropy pool */ add_sensor_randomness(regval); /* If negative, fix signal bits */ if (regval & 0x80000000) { *temp = 0xc000 | (regval >> 18); } else { *temp = (regval >> 18); } /* Detect any fault */ if (regval & MAX31855_FAULT) { snerr("ERROR: A fault was detected by MAX31855:\n"); if (regval & MAX31855_SHORT_VCC) { snerr(" The thermocouple input is shorted to VCC!\n"); } if (regval & MAX31855_SHORT_GND) { snerr(" The thermocouple input is shorted to GND!\n"); } if (regval & MAX31855_OPEN_CIRCUIT) { snerr(" The thermocouple input is not connected!\n"); } return -EINVAL; } /* Return two bytes, the temperature is fixed point Q12.2, then divide by 4 * in your application in other to get real temperature in Celsius degrees. */ return ret; } /**************************************************************************** * Name: max31855_write ****************************************************************************/ static ssize_t max31855_write(FAR struct file *filep, FAR const char *buffer, size_t buflen) { return -ENOSYS; } /**************************************************************************** * Public Functions ****************************************************************************/ /**************************************************************************** * Name: max31855_register * * Description: * This function will register the max31855 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 * MAX31855 * 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 max31855_register(FAR const char *devpath, FAR struct spi_dev_s *spi, uint16_t devid) { FAR struct max31855_dev_s *priv; int ret; /* Sanity check */ DEBUGASSERT(spi != NULL); /* Initialize the MAX31855 device structure */ priv = (FAR struct max31855_dev_s *) kmm_malloc(sizeof(struct max31855_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_max31855fops, 0666, priv); if (ret < 0) { snerr("ERROR: Failed to register driver: %d\n", ret); kmm_free(priv); } return ret; } #endif /* CONFIG_SPI && CONFIG_SENSORS_MAX31855 */