From b9f00bdbc5bdfa27ed5d78285e6258b16718614f Mon Sep 17 00:00:00 2001
From: Pascal Langer <planger@mathworks.com>
Date: Tue, 26 May 2020 12:41:33 +0200
Subject: [PATCH] Q90C: checksum fix

---
 Multiprotocol/Multiprotocol.h   |  2 +-
 Multiprotocol/NRF250K_EMU.ino   | 10 +---------
 Multiprotocol/Q90C_nrf24l01.ino | 17 ++++++++++-------
 3 files changed, 12 insertions(+), 17 deletions(-)

diff --git a/Multiprotocol/Multiprotocol.h b/Multiprotocol/Multiprotocol.h
index f2fcb11..d941c1e 100644
--- a/Multiprotocol/Multiprotocol.h
+++ b/Multiprotocol/Multiprotocol.h
@@ -19,7 +19,7 @@
 #define VERSION_MAJOR		1
 #define VERSION_MINOR		3
 #define VERSION_REVISION	1
-#define VERSION_PATCH_LEVEL	3
+#define VERSION_PATCH_LEVEL	4
 
 //******************
 // Protocols
diff --git a/Multiprotocol/NRF250K_EMU.ino b/Multiprotocol/NRF250K_EMU.ino
index cb57672..d98695c 100644
--- a/Multiprotocol/NRF250K_EMU.ino
+++ b/Multiprotocol/NRF250K_EMU.ino
@@ -192,13 +192,6 @@ static void __attribute__((unused)) XN297L_WriteEnhancedPayload(uint8_t* msg, ui
 		static uint8_t pid=0;
 
 		// address
-		if (xn297_addr_len < 4)
-		{
-			// If address length (which is defined by receive address length)
-			// is less than 4 the TX address can't fit the preamble, so the last
-			// byte goes here
-			buf[last++] = 0x55;
-		}
 		for (uint8_t i = 0; i < xn297_addr_len; ++i)
 		{
 			buf[last] = xn297_tx_addr[xn297_addr_len-i-1];
@@ -235,9 +228,8 @@ static void __attribute__((unused)) XN297L_WriteEnhancedPayload(uint8_t* msg, ui
 		// crc
 		//if (xn297_crc)
 		{
-			uint8_t offset = xn297_addr_len < 4 ? 1 : 0;
 			uint16_t crc = 0xb5d2;
-			for (uint8_t i = offset; i < last; ++i)
+			for (uint8_t i = 0; i < last; ++i)
 				crc = crc16_update(crc, buf[i], 8);
 			crc = crc16_update(crc, buf[last] & 0xc0, 2);
 			if (xn297_scramble_enabled)
diff --git a/Multiprotocol/Q90C_nrf24l01.ino b/Multiprotocol/Q90C_nrf24l01.ino
index d6c124f..63858ee 100644
--- a/Multiprotocol/Q90C_nrf24l01.ino
+++ b/Multiprotocol/Q90C_nrf24l01.ino
@@ -47,13 +47,11 @@ static void __attribute__((unused)) Q90C_send_packet()
 		packet[8] = 0;
 		packet[9] = 0;
 		packet[10] = rx_tx_addr[4];
-		packet[11] = 0x3a;									// initial checksum value ?
 	}
 	else
 	{
 		XN297L_Hopping(hopping_frequency_no++);				// RF Freq
-		if (hopping_frequency_no >= Q90C_RF_NUM_CHANNELS)
-			hopping_frequency_no = 0;
+		hopping_frequency_no %= Q90C_RF_NUM_CHANNELS;
 		packet[0]= convert_channel_8b(THROTTLE);			// 0..255
 		// A,E,R have weird scaling, 0x00-0xff range (unsigned) but center isn't 7f or 80
 		// rudder ff-7a-00
@@ -83,16 +81,21 @@ static void __attribute__((unused)) Q90C_send_packet()
 		packet[8] = 0x00;									// flags: 3 position flight mode (Angle - Horizon - Acro), VTX Toggle HIGH = next vTX frequency
 		packet[9] = 0x00;
 		packet[10] = packet_count++;
-		packet[11] = 0x9c;									// initial checksum value ?
 	}
 
-    // checksum
+    uint8_t sum=0;
+	// checksum
     for (uint8_t i = 0; i < Q90C_PACKET_SIZE - 1; i++)
-        packet[11] += packet[i];
+    {
+		sum += packet[i];
+		debug("%02X ", packet[i]);
+	}
+	packet[11] = sum ^ (IS_BIND_IN_PROGRESS? 0xc6 : 0xa4);
+	debugln("%02X",packet[11]);
 
 	XN297L_SetFreqOffset();									// Set frequency offset
-	XN297L_WriteEnhancedPayload(packet, Q90C_PACKET_SIZE, 0);
 	XN297L_SetPower();										// Set tx_power
+	XN297L_WriteEnhancedPayload(packet, Q90C_PACKET_SIZE, 0);
 }
 
 static void __attribute__((unused)) Q90C_initialize_txid()