From 9f0cdbb821a5ecec9388cc0f06db392ae7d39ae0 Mon Sep 17 00:00:00 2001
From: Pim van Pelt <pim@ipng.nl>
Date: Mon, 2 Apr 2018 22:36:46 +0200
Subject: [PATCH] Initial driver for HTU21DF

---
 src/main.c         | 25 ++++++++++++---
 src/mgos_htu21df.c | 79 ++++++++++++++++++++++++++++++++++++++++++++--
 src/mgos_sht31.c   |  1 +
 3 files changed, 99 insertions(+), 6 deletions(-)

diff --git a/src/main.c b/src/main.c
index bfc3e32..1657754 100644
--- a/src/main.c
+++ b/src/main.c
@@ -2,6 +2,7 @@
 #include "mgos_i2c.h"
 #include "mgos_sht31.h"
 #include "mgos_si7021.h"
+#include "mgos_htu21df.h"
 #include <fcntl.h>
 #include <sys/ioctl.h>
 
@@ -63,10 +64,23 @@ bool do_si7021(struct mgos_si7021 *sensor) {
   return true;
 }
 
+bool do_htu21df(struct mgos_htu21df *sensor) {
+  float temp, humid;
+
+  if (!sensor) return false;
+
+  temp=mgos_htu21df_getTemperature(sensor);
+  humid=mgos_htu21df_getHumidity(sensor);
+  LOG(LL_INFO, ("temperature=%.2fC humidity=%.1f%%", temp, humid));
+
+  return true;
+}
+
 int main() {
   struct mgos_i2c *i2c;
   struct mgos_si7021 *si7021;
   struct mgos_sht31 *sht31;
+  struct mgos_htu21df *htu21df;
 
   if (!mgos_i2c_open(I2CBUSNR)) {
     LOG(LL_ERROR, ("Cannot open I2C bus %u", I2CBUSNR));
@@ -79,22 +93,25 @@ int main() {
 
   i2c_scanner(i2c);
 
-  if (!(sht31 = mgos_sht31_create(i2c, 0x44))) {
+  if (!(sht31 = mgos_sht31_create(i2c, 0x44)))
     LOG(LL_ERROR, ("Cannot create SHT31 device"));
-  }
 
-  if (!(si7021 = mgos_si7021_create(i2c, 0x40))) {
+  if (!(si7021 = mgos_si7021_create(i2c, 0x40))) 
     LOG(LL_ERROR, ("Cannot create SI7021 device"));
-  }
+
+  if (!(htu21df = mgos_htu21df_create(i2c, 0x40))) 
+    LOG(LL_ERROR, ("Cannot create HTU21DF device"));
 
   for (;;) {
     do_sht31(sht31);
     do_si7021(si7021);
+    do_htu21df(htu21df);
     sleep(5);
   }
 
   mgos_sht31_destroy(&sht31);
   mgos_si7021_destroy(&si7021);
+  mgos_htu21df_destroy(&htu21df);
 
   return 0;
 }
diff --git a/src/mgos_htu21df.c b/src/mgos_htu21df.c
index 0de346a..e97fcac 100644
--- a/src/mgos_htu21df.c
+++ b/src/mgos_htu21df.c
@@ -22,11 +22,36 @@
 // https://cdn-shop.adafruit.com/datasheets/1899_HTU21D.pdf
 
 // Private functions follow
+static bool mgos_htu21df_cmd(struct mgos_htu21df *sensor, uint8_t cmd) {
+
+  if (!sensor || !sensor->i2c)
+    return false;
+
+  if (!mgos_i2c_write(sensor->i2c, sensor->i2caddr, &cmd, 1, true)) {
+    LOG(LL_ERROR, ("I2C=0x%02x cmd=%u (0x%02x) write error", sensor->i2caddr, cmd, cmd));
+    return false;
+  }
+  LOG(LL_DEBUG, ("I2C=0x%02x cmd=%u (0x%02x) write success", sensor->i2caddr, cmd, cmd));
+  return true;
+}
+
+static uint8_t crc8(const uint8_t *data, int len) {
+  const uint8_t poly=0x31;
+  uint8_t crc=0x00;
+
+  for (int j=len; j; --j) {
+    crc^=*data++;
+    for (int i=8; i; --i)
+      crc=(crc & 0x80) ? (crc << 1) ^ poly : (crc << 1);
+  }
+  return crc;
+}
 // Private functions end
 
 // Public functions follow
 struct mgos_htu21df *mgos_htu21df_create(struct mgos_i2c *i2c, uint8_t i2caddr) {
   struct mgos_htu21df *sensor;
+  uint8_t version;
 
   if (!i2c) return NULL;
 
@@ -36,8 +61,23 @@ struct mgos_htu21df *mgos_htu21df_create(struct mgos_i2c *i2c, uint8_t i2caddr)
   sensor->i2c=i2c;
   sensor->last_read_time=0;
 
-  LOG(LL_INFO, ("HTU21DF created at I2C 0x%02x", i2caddr));
-  return sensor;
+  mgos_htu21df_cmd(sensor, MGOS_HTU21DF_RESET);
+  mgos_usleep(25000);
+
+  mgos_htu21df_cmd(sensor, MGOS_HTU21DF_READREG);
+  if (!mgos_i2c_read(sensor->i2c, sensor->i2caddr, &version, 1, false)) {
+    LOG(LL_ERROR, ("Could not read command"));
+    free(sensor);
+    return NULL;
+  }
+  if (version == 0x02) {
+    LOG(LL_INFO, ("HTU21DF created at I2C 0x%02x", i2caddr));
+    return sensor;
+  }
+
+  LOG(LL_ERROR, ("Failed to create HTU21DF at I2C 0x%02x", i2caddr));
+  free(sensor);
+  return NULL;
 }
 
 void mgos_htu21df_destroy(struct mgos_htu21df **sensor) {
@@ -58,7 +98,42 @@ bool mgos_htu21df_read(struct mgos_htu21df *sensor) {
   }
   // Read out sensor data here 
   //
+  uint8_t data[3];
+
+  mgos_htu21df_cmd(sensor, MGOS_HTU21DF_READTEMP);
+  if (!mgos_i2c_read(sensor->i2c, sensor->i2caddr, data, 3, false)) {
+    LOG(LL_ERROR, ("Could not read command"));
+    return false;
+  }
+  if (data[2] != crc8(data, 2)) {
+    LOG(LL_ERROR, ("CRC error on temperature data"));
+    return false;
+  }
  
+  uint16_t temp = (data[0]<<8)+data[1];
+  float temperature = temp;
+  temperature *= 175.72;
+  temperature /= 65536;
+  temperature -= 46.85;
+  sensor->temperature=temperature;
+
+  mgos_htu21df_cmd(sensor, MGOS_HTU21DF_READHUM);
+  if (!mgos_i2c_read(sensor->i2c, sensor->i2caddr, data, 3, false)) {
+    LOG(LL_ERROR, ("Could not read command"));
+    return false;
+  }
+  if (data[2] != crc8(data, 2)) {
+    LOG(LL_ERROR, ("CRC error on temperature data"));
+    return false;
+  }
+ 
+  uint16_t hum = (data[0]<<8)+data[1];
+  float humidity = hum;
+  humidity *= 125;
+  humidity /= 65536;
+  humidity -= 6;
+  sensor->humidity=humidity;
+
   LOG(LL_DEBUG, ("temperature=%.2fC humidity=%.1f%%", sensor->temperature, sensor->humidity));
   sensor->last_read_time=now;
   return true;
diff --git a/src/mgos_sht31.c b/src/mgos_sht31.c
index 82ea114..9ac4757 100644
--- a/src/mgos_sht31.c
+++ b/src/mgos_sht31.c
@@ -96,6 +96,7 @@ struct mgos_sht31 *mgos_sht31_create(struct mgos_i2c *i2c, uint8_t i2caddr) {
     return sensor;
   }
 
+  LOG(LL_ERROR, ("Failed to create SHT31 at I2C 0x%02x", i2caddr));
   free(sensor);
   return NULL;
 }