From f2fb6b20de44de238019c4ed1b968a35ec535998 Mon Sep 17 00:00:00 2001
From: Bertrand Songis <bsongis@gmail.com>
Date: Mon, 28 Mar 2016 20:31:42 +0200
Subject: [PATCH] Crossfire CRC added

---
 radio/src/crc16.cpp               | 55 ++++++++++++++++++++++++++++---
 radio/src/opentx.h                |  3 +-
 radio/src/telemetry/crossfire.cpp |  9 +++--
 radio/src/tests/crossfire.cpp     |  7 ++++
 4 files changed, 65 insertions(+), 9 deletions(-)

diff --git a/radio/src/crc16.cpp b/radio/src/crc16.cpp
index d9cfbcaf8..56319e271 100644
--- a/radio/src/crc16.cpp
+++ b/radio/src/crc16.cpp
@@ -20,8 +20,8 @@
 
 #include <inttypes.h>
 
-/* CRC16 implementation according to CCITT standards */
-static const unsigned short crc16tab[256]= {
+// CRC16 implementation according to CCITT standards
+static const unsigned short crc16tab[256] = {
   0x0000,0x1021,0x2042,0x3063,0x4084,0x50a5,0x60c6,0x70e7,
   0x8108,0x9129,0xa14a,0xb16b,0xc18c,0xd1ad,0xe1ce,0xf1ef,
   0x1231,0x0210,0x3273,0x2252,0x52b5,0x4294,0x72f7,0x62d6,
@@ -56,11 +56,56 @@ static const unsigned short crc16tab[256]= {
   0x6e17,0x7e36,0x4e55,0x5e74,0x2e93,0x3eb2,0x0ed1,0x1ef0
 };
 
-uint16_t crc16(uint8_t * buf, uint32_t len)
+uint16_t crc16(const uint8_t * buf, uint32_t len)
 {
   uint16_t crc = 0;
-  for (uint32_t counter=0; counter<len; counter++) {
-    crc = (crc<<8) ^ crc16tab[ ((crc>>8) ^ *buf++ ) & 0x00FF];
+  for (uint32_t i=0; i<len; i++) {
+    crc = (crc<<8) ^ crc16tab[((crc>>8) ^ *buf++) & 0x00FF];
   }
   return crc;
 }
+
+// CRC8 implementation with polynom = x^8+x^7+x^6+x^4+x^2+1 (0xD5)
+unsigned char crc8tab[256] = {
+  0x00, 0xD5, 0x7F, 0xAA, 0xFE, 0x2B, 0x81, 0x54,
+  0x29, 0xFC, 0x56, 0x83, 0xD7, 0x02, 0xA8, 0x7D,
+  0x52, 0x87, 0x2D, 0xF8, 0xAC, 0x79, 0xD3, 0x06,
+  0x7B, 0xAE, 0x04, 0xD1, 0x85, 0x50, 0xFA, 0x2F,
+  0xA4, 0x71, 0xDB, 0x0E, 0x5A, 0x8F, 0x25, 0xF0,
+  0x8D, 0x58, 0xF2, 0x27, 0x73, 0xA6, 0x0C, 0xD9,
+  0xF6, 0x23, 0x89, 0x5C, 0x08, 0xDD, 0x77, 0xA2,
+  0xDF, 0x0A, 0xA0, 0x75, 0x21, 0xF4, 0x5E, 0x8B,
+  0x9D, 0x48, 0xE2, 0x37, 0x63, 0xB6, 0x1C, 0xC9,
+  0xB4, 0x61, 0xCB, 0x1E, 0x4A, 0x9F, 0x35, 0xE0,
+  0xCF, 0x1A, 0xB0, 0x65, 0x31, 0xE4, 0x4E, 0x9B,
+  0xE6, 0x33, 0x99, 0x4C, 0x18, 0xCD, 0x67, 0xB2,
+  0x39, 0xEC, 0x46, 0x93, 0xC7, 0x12, 0xB8, 0x6D,
+  0x10, 0xC5, 0x6F, 0xBA, 0xEE, 0x3B, 0x91, 0x44,
+  0x6B, 0xBE, 0x14, 0xC1, 0x95, 0x40, 0xEA, 0x3F,
+  0x42, 0x97, 0x3D, 0xE8, 0xBC, 0x69, 0xC3, 0x16,
+  0xEF, 0x3A, 0x90, 0x45, 0x11, 0xC4, 0x6E, 0xBB,
+  0xC6, 0x13, 0xB9, 0x6C, 0x38, 0xED, 0x47, 0x92,
+  0xBD, 0x68, 0xC2, 0x17, 0x43, 0x96, 0x3C, 0xE9,
+  0x94, 0x41, 0xEB, 0x3E, 0x6A, 0xBF, 0x15, 0xC0,
+  0x4B, 0x9E, 0x34, 0xE1, 0xB5, 0x60, 0xCA, 0x1F,
+  0x62, 0xB7, 0x1D, 0xC8, 0x9C, 0x49, 0xE3, 0x36,
+  0x19, 0xCC, 0x66, 0xB3, 0xE7, 0x32, 0x98, 0x4D,
+  0x30, 0xE5, 0x4F, 0x9A, 0xCE, 0x1B, 0xB1, 0x64,
+  0x72, 0xA7, 0x0D, 0xD8, 0x8C, 0x59, 0xF3, 0x26,
+  0x5B, 0x8E, 0x24, 0xF1, 0xA5, 0x70, 0xDA, 0x0F,
+  0x20, 0xF5, 0x5F, 0x8A, 0xDE, 0x0B, 0xA1, 0x74,
+  0x09, 0xDC, 0x76, 0xA3, 0xF7, 0x22, 0x88, 0x5D,
+  0xD6, 0x03, 0xA9, 0x7C, 0x28, 0xFD, 0x57, 0x82,
+  0xFF, 0x2A, 0x80, 0x55, 0x01, 0xD4, 0x7E, 0xAB,
+  0x84, 0x51, 0xFB, 0x2E, 0x7A, 0xAF, 0x05, 0xD0,
+  0xAD, 0x78, 0xD2, 0x07, 0x53, 0x86, 0x2C, 0xF9
+};
+
+uint8_t crc8(const uint8_t * ptr, uint32_t len)
+{
+  uint8_t crc = 0;
+  for (uint32_t i=0; i<len; i++) {
+    crc = crc8tab[crc ^ *ptr++];
+  }
+  return crc;
+}
\ No newline at end of file
diff --git a/radio/src/opentx.h b/radio/src/opentx.h
index 55d3f157a..ee0f82bfc 100644
--- a/radio/src/opentx.h
+++ b/radio/src/opentx.h
@@ -1304,7 +1304,8 @@ void evalFunctions();
 #include "telemetry/telemetry.h"
 
 #if defined(CPUARM)
-uint16_t crc16(uint8_t * buf, uint32_t len);
+uint8_t crc8(const uint8_t * ptr, uint32_t len);
+uint16_t crc16(const uint8_t * ptr, uint32_t len);
 #endif
 
 #define PLAY_REPEAT(x)            (x)                 /* Range 0 to 15 */
diff --git a/radio/src/telemetry/crossfire.cpp b/radio/src/telemetry/crossfire.cpp
index 130462ca6..041cace1d 100644
--- a/radio/src/telemetry/crossfire.cpp
+++ b/radio/src/telemetry/crossfire.cpp
@@ -68,13 +68,16 @@ void processCrossfireTelemetryFrame(uint8_t id, uint8_t subId, uint32_t value)
 
 bool checkCrossfireTelemetryFrameCRC()
 {
-  // uint8_t length = telemetryRxBuffer[1];
-  return true;
+  uint8_t len = telemetryRxBuffer[1];
+  uint8_t crc = crc8(&telemetryRxBuffer[2], len-1);
+  return (crc == telemetryRxBuffer[len+1]);
 }
 
 void processCrossfireTelemetryFrame()
 {
   if (!checkCrossfireTelemetryFrameCRC()) {
+    TRACE("processCrossfirePacket(): CRC error ");
+    DUMP(telemetryRxBuffer, TELEMETRY_RX_PACKET_SIZE);
     return;
   }
 
@@ -94,7 +97,7 @@ void processCrossfireTelemetryData(uint8_t data)
     return;
   }
 
-  if (telemetryRxBufferCount == 1 && (data <  || data > TELEMETRY_RX_PACKET_SIZE-2)) {
+  if (telemetryRxBufferCount == 1 && (data < 2 || data > TELEMETRY_RX_PACKET_SIZE-2)) {
     telemetryRxBufferCount = 0;
     return;
   }
diff --git a/radio/src/tests/crossfire.cpp b/radio/src/tests/crossfire.cpp
index cc7f69e14..317a35676 100644
--- a/radio/src/tests/crossfire.cpp
+++ b/radio/src/tests/crossfire.cpp
@@ -35,5 +35,12 @@ TEST(Crossfire, createCrossfireFrame)
 
   // TODO check
 }
+
+TEST(Crossfire, crc8)
+{
+  uint8_t frame[] = { 0x00, 0x0C, 0x14, 0x00, 0x00, 0x00, 0x00, 0xFF, 0x01, 0x03, 0x00, 0x00, 0x00, 0xF4 };
+  uint8_t crc = crc8(&frame[2], frame[1]-1);
+  ASSERT_EQ(frame[frame[1]+1], crc);
+}
 #endif