SG112A: Add CRC Check for Sensor Messages, Code Cleanup, Comments

lib/SG112A/SG112A.cpp

@@ -1,6 +1,33 @@
+/*
+  SG112A.cpp - SG112A Sensor Library
+  Copyright (c) 2020-2021, Stefan Brand
+  All rights reserved.
+  Redistribution and use in source and binary forms, with or without
+  modification, are permitted provided that the following conditions are met:
+  1. Redistributions of source code must retain the above copyright notice, this
+     list of conditions and the following disclaimer.
+  2. Redistributions in binary form must reproduce the above copyright notice,
+     this list of conditions and the following disclaimer in the documentation
+     and/or other materials provided with the distribution.
+  3. Neither the name of the copyright holder nor the names of its
+     contributors may be used to endorse or promote products derived from
+     this software without specific prior written permission.
+  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+  DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+  SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+  CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
 #include <Arduino.h>
 #include "SG112A.h"
 
+// Constructor - Inititalize Hardware UART
 SG112A::SG112A(void) {
     Serial.begin(9600);
     Serial.setTimeout(READ_TIMEOUT);
@@ -20,6 +47,7 @@ void SG112A::getSensorData(lora_data &loradata) {
     }
 }
 
+// Write a Command to the Sensor
 void SG112A::write(byte cmd) {
     uint8_t _cmd[6] = {0xAA, 0x55, cmd, 0x00, 0x00, 0x00};
     uint16_t crc = crc16(_cmd, 4);
@@ -30,26 +58,37 @@ void SG112A::write(byte cmd) {
     Serial.flush();
 }
 
+// Read a Sensor Response
 uint8_t SG112A::read() {
+    // Number of returned Bytes
     uint8_t ret = 0;
+    // Clear Internal Buffer
     zeroBuffer();
+
+    // Read Available Bytes
     if (Serial.available() > 0) {
       ret = Serial.readBytes(buffer, SER_BUF_LEN);
     }
 
-    if (buffer[0] != 0xBB && buffer[1] != 0x66)
+    // Check Sync Bytes
-        ret = 0;
+    if (buffer[0] != 0xBB || buffer[1] != 0x66)
-
+      return 0;
-    // TODO: Do CRC Check Here
+   
+    // Check CRC of the Returned Messages
+    uint16_t crc = crc16(buffer, ret-2);
+    if (buffer[ret-1] != (uint8_t)(crc >> 8) || buffer[ret-2] != (uint8_t)(crc & 0xFF))
+      return 0;
 
     return ret;
 }
 
+// Fill the Internal Buffer with Zeroes
 void SG112A::zeroBuffer() {
     for (int i=0; i < SER_BUF_LEN; i++)
         buffer[i] = 0x00;
 }
 
+// Calculate 16Bit CRC of Messages and Commands
 uint16_t SG112A::crc16(uint8_t *cmd, int len){
   uint16_t ret = 0xffff;
   uint16_t polynomial = 0xa001;
@@ -71,4 +110,4 @@ uint16_t SG112A::crc16(uint8_t *cmd, int len){
     }
   }      
   return ret;
-}
+}

lib/SG112A/SG112A.h

@@ -1,17 +1,44 @@
+/*
+  SG112A.h - SG112A Sensor Library
+  Copyright (c) 2020-2021, Stefan Brand
+  All rights reserved.
+  Redistribution and use in source and binary forms, with or without
+  modification, are permitted provided that the following conditions are met:
+  1. Redistributions of source code must retain the above copyright notice, this
+     list of conditions and the following disclaimer.
+  2. Redistributions in binary form must reproduce the above copyright notice,
+     this list of conditions and the following disclaimer in the documentation
+     and/or other materials provided with the distribution.
+  3. Neither the name of the copyright holder nor the names of its
+     contributors may be used to endorse or promote products derived from
+     this software without specific prior written permission.
+  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+  DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+  SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+  CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
 #ifndef SG112A_H
 #define SG112A_H
 
+// Data Structure for the LoRa Packet
 struct lora_data {
   uint8_t bat;
   int16_t ppm;
 } __attribute__ ((packed));
 
-#define READ_TIMEOUT 500
+#define READ_TIMEOUT 500  // Timeout for Serial Communication
-#define SER_BUF_LEN  16
+#define SER_BUF_LEN  16   // Length of the Internal Serial Message Buffer
 
-#define CMD_GET_VER 0x10
+#define CMD_GET_VER 0x10  // Get Sensor Version
-#define CMD_GET_SER 0x12
+#define CMD_GET_SER 0x12  // Get Sensor Serial
-#define CMD_GET_PPM 0x14
+#define CMD_GET_PPM 0x14  // Get Current PPM Reading
 
 class SG112A {
   private: