From 29a139559d2af070a8dcc11ebab313e6a07e2865 Mon Sep 17 00:00:00 2001
From: Damjan Adamic <projectkk2glider@gmail.com>
Date: Thu, 19 May 2016 06:30:19 +0200
Subject: [PATCH] =?UTF-8?q?Re=20#2999:=20More=20strict=20SBUS=20frame=20ch?=
 =?UTF-8?q?eck=20(only=20allow=2025=20byte=20frames,=20ch=E2=80=A6=20(#350?=
 =?UTF-8?q?1)?=
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* Re #2999: More strict SBUS frame check (only allow 25 byte frames, check end byte)

* SBUS fixes
---
 radio/src/sbus.cpp | 37 ++++++++++++++++---------------------
 radio/src/sbus.h   |  3 +--
 2 files changed, 17 insertions(+), 23 deletions(-)

diff --git a/radio/src/sbus.cpp b/radio/src/sbus.cpp
index f2cddc188..575e5dfa6 100644
--- a/radio/src/sbus.cpp
+++ b/radio/src/sbus.cpp
@@ -24,40 +24,31 @@
 #define SBUS_FRAME_GAP_DELAY   1000 // 500uS
 
 #define SBUS_START_BYTE        0x0F
+#define SBUS_END_BYTE          0x00
 #define SBUS_FLAGS_IDX         23
 #define SBUS_FRAMELOST_BIT     2
 #define SBUS_FAILSAFE_BIT      3
 
-#define SBUS_CH_BITS          11
-#define SBUS_CH_MASK          ((1<<SBUS_CH_BITS)-1)
+#define SBUS_CH_BITS           11
+#define SBUS_CH_MASK           ((1<<SBUS_CH_BITS)-1)
 
-#define SBUS_CH_CENTER        0x3E0
+#define SBUS_CH_CENTER         0x3E0
 
-uint8_t SbusFrame[SBUS_MAX_FRAME_SIZE];
-uint16_t SbusTimer ;
-uint8_t SbusIndex = 0 ;
 
 // Range for pulses (ppm input) is [-512:+512]
 void processSbusFrame(uint8_t * sbus, int16_t * pulses, uint32_t size)
 {
-  uint32_t inputbitsavailable = 0;
-  uint32_t inputbits = 0;
-
-  if (sbus[0] != SBUS_START_BYTE) {
+  if (size != SBUS_FRAME_SIZE || sbus[0] != SBUS_START_BYTE || sbus[SBUS_FRAME_SIZE-1] != SBUS_END_BYTE) {
     return; // not a valid SBUS frame
   }
-
-  if (size < SBUS_MIN_FRAME_SIZE) {
-    return;
-  }
-
-  if (size > SBUS_FLAGS_IDX && ((sbus[SBUS_FLAGS_IDX] & (1<<SBUS_FAILSAFE_BIT)) || (sbus[SBUS_FLAGS_IDX] & (1<<SBUS_FRAMELOST_BIT)))) {
+  if ((sbus[SBUS_FLAGS_IDX] & (1<<SBUS_FAILSAFE_BIT)) || (sbus[SBUS_FLAGS_IDX] & (1<<SBUS_FRAMELOST_BIT))) {
     return; // SBUS invalid frame or failsafe mode
   }
 
-  // Skip start byte
-  sbus++;
+  sbus++;   // skip start byte
 
+  uint32_t inputbitsavailable = 0;
+  uint32_t inputbits = 0;
   for (uint32_t i=0; i<NUM_TRAINER; i++) {
     while (inputbitsavailable < SBUS_CH_BITS) {
       inputbits |= *sbus++ << inputbitsavailable;
@@ -76,12 +67,16 @@ void processSbusInput()
 #if !defined(SIMU)
   uint8_t rxchar;
   uint32_t active = 0;
+  static uint8_t SbusIndex = 0;
+  static uint16_t SbusTimer;
+  static uint8_t SbusFrame[SBUS_FRAME_SIZE];
+
   while (sbusGetByte(&rxchar)) {
     active = 1;
-    SbusFrame[SbusIndex++] = rxchar;
-    if (SbusIndex > SBUS_MAX_FRAME_SIZE-1) {
-      SbusIndex = SBUS_MAX_FRAME_SIZE-1;
+    if (SbusIndex > SBUS_FRAME_SIZE-1) {
+      SbusIndex = SBUS_FRAME_SIZE-1;
     }
+    SbusFrame[SbusIndex++] = rxchar;
   }
   if (active) {
     SbusTimer = getTmr2MHz();
diff --git a/radio/src/sbus.h b/radio/src/sbus.h
index 5ef7359a5..f9ea5c325 100644
--- a/radio/src/sbus.h
+++ b/radio/src/sbus.h
@@ -22,8 +22,7 @@
 #define _SBUS_H_
 
 #define SBUS_BAUDRATE         100000
-#define SBUS_MIN_FRAME_SIZE   23
-#define SBUS_MAX_FRAME_SIZE   28
+#define SBUS_FRAME_SIZE       25
 
 void processSbusInput();