rssi: calculate signal and noise in firmware

firmware/bluetooth_rxtx/bluetooth_rxtx.c

@@ -68,7 +68,7 @@ volatile uint8_t modulation = MOD_BT_BASIC_RATE;
 /* specan stuff */
 volatile uint16_t low_freq = 2400;
 volatile uint16_t high_freq = 2483;
-volatile int8_t rssi_threshold = -30;  // -54dBm - 30 = -84dBm
+volatile int8_t rssi_threshold = -84;
 
 /* Generic TX stuff */
 generic_tx_packet tx_pkt;
@@ -140,10 +140,12 @@ static int enqueue(uint8_t type, uint8_t* buf)
 		f->clkn_high = idle_buf_clkn_high;
 		f->clk100ns = idle_buf_clk100ns;
 		f->channel = (uint8_t)((idle_buf_channel - 2402) & 0xff);
-		f->rssi_min = rssi_min;
-		f->rssi_max = rssi_max;
-		f->rssi_avg = rssi_get_avg(idle_buf_channel);
-		f->rssi_count = rssi_count;
+		f->rssi_min = rssi_get_min();
+		f->rssi_max = rssi_get_max();
+		f->rssi_noise = rssi_get_noise();
+		f->rssi_signal = rssi_get_signal();
+		f->rssi_avg = rssi_get_avg();
+		f->rssi_count = rssi_get_cnt();
 	}
 
 	memcpy(f->data, buf, DMA_SIZE);
@@ -400,7 +402,7 @@ static int vendor_request_handler(uint8_t request, uint16_t* request_params, uin
 	case UBERTOOTH_LED_SPECAN:
 		if (request_params[0] > 256)
 			return 0;
-		rssi_threshold = 54 - request_params[0];
+		rssi_threshold = request_params[0];
 		requested_mode = MODE_LED_SPECAN;
 		*data_len = 0;
 		break;
@@ -1270,12 +1272,11 @@ void bt_stream_rx()
 		 * at multiple trigger points there. The MAX() below
 		 * helps with statistics in the case that cs_trigger
 		 * happened before the loop started. */
-		rssi_reset();
 		rssi_at_trigger = INT8_MIN;
 		while (!rx_tc) {
-			rssi = (int8_t)(cc2400_get(RSSI) >> 8);
+			rssi = cc2400_rssi();
 			if (cs_trigger && (rssi_at_trigger == INT8_MIN)) {
-				rssi = MAX(rssi,(cs_threshold_cur+54));
+				rssi = MAX(rssi, cs_threshold_cur);
 				rssi_at_trigger = rssi;
 			}
 			rssi_add(rssi);
@@ -1284,6 +1285,7 @@ void bt_stream_rx()
 
 			/* If timer says time to hop, do it. */
 			if (do_hop) {
+				rssi_reset();
 				hop();
 			} else {
 				TXLED_CLR;
@@ -1307,8 +1309,6 @@ void bt_stream_rx()
 			dma_discard = 0;
 		}
 
-		rssi_iir_update(channel);
-
 		/* Set squelch hold if there was either a CS trigger, squelch
 		 * is disabled, or if the current rssi_max is above the same
 		 * threshold. Currently, this is redundant, but allows for
@@ -1318,12 +1318,14 @@ void bt_stream_rx()
 			cs_trigger = 0;
 		}
 
-		if (rssi_max >= (cs_threshold_cur + 54)) {
+		if (rssi_get_max() >= cs_threshold_cur) {
 			status |= RSSI_TRIGGER;
 		}
 
 		enqueue(BR_PACKET, (uint8_t*)idle_rxbuf);
 
+		rssi_reset();
+
 		handle_usb(clkn);
 		rx_tc = 0;
 		rx_err = 0;
@@ -1548,9 +1550,9 @@ void bt_generic_le(u8 active_mode)
 		rssi_at_trigger = INT8_MIN;
 		while ((rx_tc == 0) && (rx_err == 0))
 		{
-			rssi = (int8_t)(cc2400_get(RSSI) >> 8);
+			rssi = cc2400_rssi();
 			if (cs_trigger && (rssi_at_trigger == INT8_MIN)) {
-				rssi = MAX(rssi,(cs_threshold_cur+54));
+				rssi = MAX(rssi,cs_threshold_cur);
 				rssi_at_trigger = rssi;
 			}
 			rssi_add(rssi);
@@ -1568,8 +1570,6 @@ void bt_generic_le(u8 active_mode)
 		if (rx_tc > 1)
 			status |= DMA_OVERFLOW;
 
-		rssi_iir_update(channel);
-
 		/* Set squelch hold if there was either a CS trigger, squelch
 		 * is disabled, or if the current rssi_max is above the same
 		 * threshold. Currently, this is redundant, but allows for
@@ -1580,7 +1580,7 @@ void bt_generic_le(u8 active_mode)
 			cs_trigger = 0;
 		}
 
-		if (rssi_max >= (cs_threshold_cur + 54)) {
+		if (rssi_get_max(channel) >= cs_threshold_cur) {
 			status |= RSSI_TRIGGER;
 			hold = CS_HOLD_TIME;
 		}
@@ -1670,8 +1670,8 @@ void bt_le_sync(u8 active_mode)
 		while ((rx_tc == 0) && (rx_err == 0) && (do_hop == 0) && requested_mode == active_mode)
 			;
 
-		rssi = (int8_t)(cc2400_get(RSSI) >> 8);
-		rssi_min = rssi_max = rssi;
+		rssi = cc2400_rssi();
+		rssi_add(rssi);
 
 		if (requested_mode != active_mode) {
 			goto cleanup;
@@ -1747,6 +1747,8 @@ void bt_le_sync(u8 active_mode)
 		enqueue(LE_PACKET, (uint8_t *)packet);
 		le.last_packet = CLK100NS;
 
+		rssi_reset();
+
 	rx_flush:
 		// this might happen twice, but it's safe to do so
 		cc2400_strobe(SFSON);
@@ -2438,7 +2440,7 @@ void specan()
 			volatile u32 j = 500; while (--j); //FIXME crude delay
 			buf[3 * i] = (f >> 8) & 0xFF;
 			buf[(3 * i) + 1] = f  & 0xFF;
-			buf[(3 * i) + 2] = cc2400_get(RSSI) >> 8;
+			buf[(3 * i) + 2] = cc2400_rssi();
 			i++;
 			if (i == 16) {
 				enqueue(SPECAN, buf);
@@ -2484,7 +2486,7 @@ void led_specan()
 
 		/* give the CC2400 time to acquire RSSI reading */
 		volatile u32 j = 500; while (--j); //FIXME crude delay
-		lvl = (int8_t)((cc2400_get(RSSI) >> 8) & 0xff);
+		lvl = cc2400_rssi();
 		if (lvl > rssi_threshold) {
 			switch (i) {
 				case 0:

firmware/bluetooth_rxtx/ubertooth_rssi.c

@@ -23,58 +23,101 @@
 
 #include <string.h>
 
-#define RSSI_IIR_ALPHA 3       // 3/256 = .012
+#define RINGBUFFER_SIZE 40
 
-int32_t rssi_sum;
-int16_t rssi_iir[79] = {0};
+size_t pointer = 0;
+size_t size = 0;
+int8_t values[RINGBUFFER_SIZE] = {0};
+
+int8_t max = -120;
+int8_t min = 0;
 
 void rssi_reset(void)
 {
-	memset(rssi_iir, 0, sizeof(rssi_iir));
+	memset(values, 0, size);
+	pointer = 0;
+	size = 0;
 
-	rssi_count = 0;
-	rssi_sum = 0;
-	rssi_max = INT8_MIN;
-	rssi_min = INT8_MAX;
+	max = -120;
+	min = 0;
 }
 
 void rssi_add(int8_t v)
 {
-	rssi_max = (v > rssi_max) ? v : rssi_max;
-	rssi_min = (v < rssi_min) ? v : rssi_min;
-	rssi_sum += ((int32_t)v * 256);  // scaled int math (x256)
-	rssi_count += 1;
+	max = (v > max) ? v : max;
+	min = (v < min) ? v : min;
+
+	values[pointer] = v;
+	pointer = (pointer + 1) % RINGBUFFER_SIZE;
+
+	size = size < RINGBUFFER_SIZE ? size + 1 : RINGBUFFER_SIZE;
+}
+
+int8_t rssi_get_avg()
+{
+	int32_t sum = 0;
+
+	for (size_t i = 0; i < size; i++)
+	{
+		sum += values[i];
+	}
+
+	uint8_t avg = (int8_t)(sum / (int)size);
+
+	return avg;
 }
 
-/* For sweep mode, update IIR per channel. Otherwise, use single value. */
-void rssi_iir_update(uint16_t channel)
+int8_t rssi_get_signal()
 {
-	int32_t avg;
-	int32_t rssi_iir_acc;
-
-	/* Use array to track 79 Bluetooth channels, or just first slot
-	 * of array if the frequency is not a valid Bluetooth channel. */
-	if ( channel < 2402 || channel < 2480 )
-		channel = 2402;
-
-	int i = channel - 2402;
-
-	// IIR using scaled int math (x256)
-	if (rssi_count != 0)
-		avg = (rssi_sum  + 128) / rssi_count;
-	else
-		avg = 0; // really an error
-	rssi_iir_acc = rssi_iir[i] * (256-RSSI_IIR_ALPHA);
-	rssi_iir_acc += avg * RSSI_IIR_ALPHA;
-	rssi_iir[i] = (int16_t)((rssi_iir_acc + 128) / 256);
+	int32_t sum = 0;
+	size_t num = 0;
+	int8_t avg = ((int16_t)min + (int16_t)max) / 2;
+
+	for (size_t i = 0; i < size; i++)
+	{
+		if (values[i] > avg)
+		{
+			sum += values[i];
+			num++;
+		}
+	}
+
+	int8_t signal = (int8_t)(sum / (int)num);
+
+	return signal;
 }
 
-int8_t rssi_get_avg(uint16_t channel)
+int8_t rssi_get_noise()
 {
-	/* Use array to track 79 Bluetooth channels, or just first slot
-	 * of array if the frequency is not a valid Bluetooth channel. */
-	if ( channel < 2402 || channel < 2480 )
-		channel = 2402;
+	int32_t sum = 0;
+	size_t num = 0;
+	int8_t avg = ((int16_t)min + (int16_t)max) / 2;
 
-	return (rssi_iir[channel-2402] + 128) / 256;
+	for (size_t i = 0; i < size; i++)
+	{
+		if (values[i] <= avg)
+		{
+			sum += values[i];
+			num++;
+		}
+	}
+
+	int8_t noise = (int8_t)(sum / (int)num);
+
+	return noise;
+}
+
+uint8_t rssi_get_cnt()
+{
+	return (uint8_t)size;
+}
+
+int8_t rssi_get_min()
+{
+	return min;
+}
+
+int8_t rssi_get_max()
+{
+	return max;
 }

firmware/bluetooth_rxtx/ubertooth_rssi.h

@@ -24,13 +24,13 @@
 
 #include "inttypes.h"
 
-int8_t rssi_max;
-int8_t rssi_min;
-uint8_t rssi_count;
-
-void rssi_reset(void);
+void rssi_reset();
 void rssi_add(int8_t v);
-void rssi_iir_update(uint16_t channel);
-int8_t rssi_get_avg(uint16_t channel);
+int8_t rssi_get_avg();
+int8_t rssi_get_signal();
+int8_t rssi_get_noise();
+int8_t rssi_get_min();
+int8_t rssi_get_max();
+uint8_t rssi_get_cnt();
 
 #endif

firmware/common/ubertooth.c

@@ -64,7 +64,7 @@ void wait_us(u32 us)
  */
 void gpio_init()
 {
-	/* 
+	/*
 	 * Set all pins for GPIO.  This shouldn't be necessary after a reset, but
 	 * we might get called at other times.
 	 */
@@ -306,6 +306,11 @@ u16 cc2400_get(u8 reg)
 	return in & 0xFFFF;
 }
 
+int8_t cc2400_rssi()
+{
+	return (int8_t)(cc2400_get(RSSI) >> 8) - 54;
+}
+
 /* write 16 bit value to a register */
 void cc2400_set(u8 reg, u16 val)
 {
@@ -374,7 +379,7 @@ void cc2400_fifo_write(u8 len, u8 *data) {
 		SCLK_SET;
 		SCLK_CLR;
 	}
-	
+
 	spi_delay();
 	/* end transaction by raising CSN */
 	CSN_SET;
@@ -531,9 +536,9 @@ void reset()
 	USRLED_CLR;
 	WDMOD |= WDMOD_WDEN | WDMOD_WDRESET;
 	WDFEED_SEQUENCE;
-	
+
 	/* Set watchdog timeout to 256us (minimum) */
-	
+
 	/* sleep for 1s (minimum) */
 	wait(1);
 }
@@ -633,7 +638,7 @@ void get_part_num(uint8_t *buffer, int *len)
 	buffer[3] = (result[1] >> 16) & 0xFF;
 	buffer[4] = (result[1] >> 24) & 0xFF;
 	*len = 5;
-	
+
 }
 
 void get_device_serial(uint8_t *buffer, int *len)

firmware/common/ubertooth.h

@@ -323,6 +323,7 @@ void atest_init(void);
 void cc2400_init(void);
 u32 cc2400_spi(u8 len, u32 data);
 u16 cc2400_get(u8 reg);
+int8_t cc2400_rssi();
 void cc2400_set(u8 reg, u16 val);
 u8 cc2400_get8(u8 reg);
 void cc2400_set8(u8 reg, u8 val);