From cb64ae7e0f3fd45d61706d74b5a03fe7bcb0f037 Mon Sep 17 00:00:00 2001
From: RedHawk <tadshig@gmail.com>
Date: Tue, 13 Jun 2023 19:52:53 +0300
Subject: [PATCH] temp: [#61] CRC check.

---
 .../threads/temperature/SensorTempSHT20.cpp   | 40 ++++++++-----------
 .../src/threads/temperature/SensorTempSHT20.h |  2 +
 2 files changed, 18 insertions(+), 24 deletions(-)

diff --git a/source/shoh/src/threads/temperature/SensorTempSHT20.cpp b/source/shoh/src/threads/temperature/SensorTempSHT20.cpp
index 73be084..db72284 100644
--- a/source/shoh/src/threads/temperature/SensorTempSHT20.cpp
+++ b/source/shoh/src/threads/temperature/SensorTempSHT20.cpp
@@ -31,7 +31,7 @@ SensorTempSHT20::SensorTempSHT20(I2C* pi2c)
 : _pi2c(pi2c), _dev_addr(0x40), _up_flag(false),
 _com_read_hold(0xe3), _com_read_nohold(0xf3),
 _com_write_ur(0xe6), _com_read_ur(0xe7),
-_com_soft_reset(0xfe)
+_com_soft_reset(0xfe), _polynominal(0x131)
 {
   this->read();
 }
@@ -71,32 +71,24 @@ uint16_t SensorTempSHT20::read()
   raw_temp |= (rbuf[0] << 8);
   raw_temp |= (rbuf[1] & 0xfc);
   crc = rbuf[2];
-  LOG_WARNING("Raw data: %04x; CRC: %x", raw_temp, crc);
-
-  //TODO: crc check here.
 
+  if (this->crc_check(rbuf, 2, crc))
+    LOG_WARNING("Temperature sensor reported crc mismatch.\nRaw data: %04x; CRC: %x", raw_temp, crc);
+  
   return raw_temp;
 }
 
-/*
-const int16_t POLYNOMIAL = 0x131;
-
-int8_t SHT2x_CheckCrc(int8_t data[], int8_t nbrOfBytes, int8_t checksum)
+bool SensorTempSHT20::crc_check(uint8_t * data, uint8_t nbrOfBytes, uint8_t checksum)
 {
-    int8_t crc = 0;
-    int8_t bit;
-    int8_t byteCtr;
-    //calculates 8-Bit checksum with given polynomial
-    for (byteCtr = 0; byteCtr < nbrOfBytes; ++byteCtr)
-    {
-        crc ^= (data[byteCtr]);
-        for ( bit = 8; bit > 0; --bit)
-        {
-            if (crc & 0x80) crc = (crc << 1) ^ POLYNOMIAL;
-            else crc = (crc << 1);
-        }
-    }
-    if (crc != checksum) return 1;
-    else return 0;
+  uint8_t crc = 0;
+  uint8_t bit;
+  uint8_t byteCtr;
+  //Calculates 8-Bit checksum with given _polynomial
+  for (byteCtr = 0; byteCtr < nbrOfBytes; ++byteCtr)
+  {
+    crc ^= (data[byteCtr]);
+    for ( bit = 8; bit > 0; --bit)
+      crc = (crc & 0x80) ? ((crc << 1) ^ this->_polynominal) : (crc << 1);
+  }
+  return crc != checksum;
 }
-*/
diff --git a/source/shoh/src/threads/temperature/SensorTempSHT20.h b/source/shoh/src/threads/temperature/SensorTempSHT20.h
index 1dcd5c2..6006bc3 100644
--- a/source/shoh/src/threads/temperature/SensorTempSHT20.h
+++ b/source/shoh/src/threads/temperature/SensorTempSHT20.h
@@ -18,6 +18,7 @@ public:
   bool is_up();
 private:
   uint16_t read();
+  bool crc_check(uint8_t * data, uint8_t nbrOfBytes, uint8_t checksum);
 
   I2C* _pi2c;
   const uint8_t _dev_addr;
@@ -27,6 +28,7 @@ private:
   const uint8_t _com_write_ur; //user register
   const uint8_t _com_read_ur; //user register
   const uint8_t _com_soft_reset;
+  const uint16_t _polynominal;
 };
 
 #endif /* THREADS_TEMPERATURE_SENSORTEMPSHT20_H_ */