protocol_splitter: including magic number on XOR for checksum

src/drivers/protocol_splitter/protocol_splitter.cpp

@@ -86,7 +86,7 @@ typedef union __attribute__((packed))
 		uint8_t len_h:	7,         // Length MSB
 			 type:	1;         // 0=MAVLINK, 1=RTPS
 		uint8_t len_l;             // Length LSB
-		uint8_t checksum;          // XOR of two above bytes
+		uint8_t checksum;          // XOR of the three bytes above
 	} fields;
 } Sp2Header_t;
 
@@ -352,7 +352,7 @@ ssize_t Mavlink2Dev::read(struct file *filp, char *buffer, size_t buflen)
 	       (((Sp2Header_t *) &_read_buffer->buffer[i])->fields.magic != Sp2HeaderMagic
 		|| ((Sp2Header_t *) &_read_buffer->buffer[i])->fields.type != (uint8_t)MessageType::Mavlink
 		|| ((Sp2Header_t *) &_read_buffer->buffer[i])->fields.checksum !=
-		(_read_buffer->buffer[i + 1] ^ _read_buffer->buffer[i + 2])
+		(_read_buffer->buffer[i] ^ _read_buffer->buffer[i + 1] ^ _read_buffer->buffer[i + 2])
 	       )) {
 		i++;
 	}
@@ -446,7 +446,7 @@ ssize_t Mavlink2Dev::write(struct file *filp, const char *buffer, size_t buflen)
 			} else {
 				_header.fields.len_h = (buflen >> 8) & 0x7f;
 				_header.fields.len_l = buflen & 0xff;
-				_header.fields.checksum = _header.bytes[1] ^ _header.bytes[2];
+				_header.fields.checksum = _header.bytes[0] ^ _header.bytes[1] ^ _header.bytes[2];
 				::write(_fd, _header.bytes, 4);
 				ret = ::write(_fd, buffer, buflen);
 			}
@@ -519,7 +519,7 @@ ssize_t RtpsDev::read(struct file *filp, char *buffer, size_t buflen)
 	       (((Sp2Header_t *) &_read_buffer->buffer[i])->fields.magic != Sp2HeaderMagic
 		|| ((Sp2Header_t *) &_read_buffer->buffer[i])->fields.type != (uint8_t)MessageType::Rtps
 		|| ((Sp2Header_t *) &_read_buffer->buffer[i])->fields.checksum !=
-		(_read_buffer->buffer[i + 1] ^ _read_buffer->buffer[i + 2])
+		(_read_buffer->buffer[i] ^ _read_buffer->buffer[i + 1] ^ _read_buffer->buffer[i + 2])
 	       )) {
 		i++;
 	}
@@ -595,7 +595,7 @@ ssize_t RtpsDev::write(struct file *filp, const char *buffer, size_t buflen)
 			} else {
 				_header.fields.len_h = (buflen >> 8) & 0x7f;
 				_header.fields.len_l = buflen & 0xff;
-				_header.fields.checksum = _header.bytes[1] ^ _header.bytes[2];
+				_header.fields.checksum = _header.bytes[0] ^ _header.bytes[1] ^ _header.bytes[2];
 				::write(_fd, _header.bytes, 4);
 				ret = ::write(_fd, buffer, buflen);
 			}