sbus: remove unused variables & improve some comments

src/lib/rc/sbus.cpp

@@ -76,12 +76,6 @@
 // this is the rate of the old code
 #define SBUS1_DEFAULT_RATE_HZ	72
 
-#define SBUS_SINGLE_CHAR_LEN_US		(1/((100000/10)) * 1000 * 1000)
-
-#define SBUS_FRAME_INTERVAL_US	2500
-#define SBUS_MIN_CALL_INTERVAL_US	(SBUS_FRAME_GAP_US / 3)
-#define SBUS_EPSILON_US	2500
-
 /*
   Measured values with Futaba FX-30/R6108SB:
     -+100% on TX:  PCM 1.100/1.520/1.950ms -> SBus raw values: 350/1024/1700  (100% ATV)
@@ -105,7 +99,6 @@
 #define SBUS_SCALE_OFFSET (int)(SBUS_TARGET_MIN - (SBUS_SCALE_FACTOR * SBUS_RANGE_MIN + 0.5f))
 
 static hrt_abstime last_rx_time;
-static hrt_abstime last_frame_time;
 static hrt_abstime last_txframe_time = 0;
 
 #define SBUS2_FRAME_SIZE_RX_VOLTAGE	3
@@ -229,7 +222,6 @@ sbus_config(int sbus_fd, bool singlewire)
 		/* initialise the decoder */
 		partial_frame_count = 0;
 		last_rx_time = hrt_absolute_time();
-		last_frame_time = last_rx_time;
 		sbus_frame_drops = 0;
 
 		ret = 0;
@@ -404,8 +396,7 @@ sbus_parse(uint64_t now, uint8_t *frame, unsigned len, uint16_t *values,
 				}
 
 				/*
-				 * Great, it looks like we might have a frame.  Go ahead and
-				 * decode it.
+				 * Great, it looks like we might have a frame. Go ahead and decode it.
 				 */
 				decode_ret = sbus_decode(now, sbus_frame, values, num_values, sbus_failsafe, sbus_frame_drop, max_channels);
 
@@ -582,7 +573,7 @@ sbus_decode(uint64_t frame_time, uint8_t *frame, uint16_t *values, uint16_t *num
 {
 
 	/* check frame boundary markers to avoid out-of-sync cases */
-	if ((frame[0] != SBUS_START_SYMBOL)) {
+	if (frame[0] != SBUS_START_SYMBOL) {
 		sbus_frame_drops++;
 #if defined(SBUS_DEBUG_LEVEL) && SBUS_DEBUG_LEVEL > 0
 		printf("DECODE FAIL: ");
@@ -597,6 +588,7 @@ sbus_decode(uint64_t frame_time, uint8_t *frame, uint16_t *values, uint16_t *num
 		return false;
 	}
 
+	/* the last byte in the frame indicates what frame will follow after this one */
 	switch (frame[24]) {
 	case 0x00:
 		/* this is S.BUS 1 */
@@ -632,8 +624,6 @@ sbus_decode(uint64_t frame_time, uint8_t *frame, uint16_t *values, uint16_t *num
 	}
 
 	/* we have received something we think is a frame */
-	last_frame_time = frame_time;
-
 	unsigned chancount = (max_values > SBUS_INPUT_CHANNELS) ?
 			     SBUS_INPUT_CHANNELS : max_values;