add RSSI evaluation to packet handler, closes #2

main.c

@@ -114,12 +114,20 @@ int main(void)
 			uart_send_string(str_output_buffer);
 			uart_send_string("dBm\r\n");
 			uart_send_string("error: ");
-			if (error == PH_ERROR_NOEND)
+			switch (error) {
+			case PH_ERROR_NOEND:
 				uart_send_string("no end flag");
-			else if (error == PH_ERROR_STUFFBIT)
+				break;
+			case PH_ERROR_STUFFBIT:
 				uart_send_string("invalid stuff bit");
-			else if (error == PH_ERROR_CRC)
+				break;
+			case PH_ERROR_CRC:
 				uart_send_string("CRC error");
+				break;
+			case PH_ERROR_RSSI_DROP:
+				uart_send_string("RSSI drop");
+				break;
+			}
 			uart_send_string("\r\n");
 			ph_loop();							// house keeping, sending over UART takes time
 		}

packet_handler.c

@@ -19,11 +19,13 @@
 #define LED1_OFF 	P1OUT &= ~LED1
 #define LED1_TOGGLE	P1OUT ^= LED1
 
-// sync word for AIS
+// sync word for AIS - only used for test
 #define AIS_SYNC_WORD		0x7e
 
+// paramters for package detection
 #define PH_PREAMBLE_LENGTH	8		// minimum number of alternating bits we need for a valid preamble
 #define PH_SYNC_TIMEOUT	16			// number of bits we wait for a preamble to start before changing channel
+#define PH_RSSI_THRESHOLD -95		// threshold in dBm for valid signal, comment out to ignore signal strength
 
 // pins that packet handler uses to receive data
 #define	PH_DATA_CLK_PIN		BIT2	// 2.2 RX data clock
@@ -79,8 +81,14 @@ void ph_setup(void)
 // start packet handler operation, including ISR
 void ph_start(void)
 {
-	// start radio, wait until it's spun up
+
 #ifndef TEST
+	#ifdef PH_RSSI_THRESHOLD
+	// set radio RSSI threshold
+	radio_set_property(0x20, 0x4a, RADIO_DBM_TO_RSSI(PH_RSSI_THRESHOLD));
+	#endif
+
+	// start radio, wait until it's spun up
 	radio_start_rx(ph_radio_channel, 0, 0, RADIO_STATE_NO_CHANGE, RADIO_STATE_NO_CHANGE, RADIO_STATE_NO_CHANGE);
 	radio_wait_for_CTS();
 #endif
@@ -195,14 +203,22 @@ __interrupt void ph_irq_handler(void)
 
 			case PH_SYNC_FLAG:								// sub-state: start flag detection
 				rx_sync_count--;							// count down bits
+#ifndef TEST
+#ifdef PH_RSSI_THRESHOLD
+				if (!RADIO_SIGNAL) {						// if we don't have a stable signal
+					ph_state = PH_STATE_RESET;					// abort sync and reset state machine
+					break;
+				}
+#endif
+#endif
 				if (rx_sync_count != 0) {					// if this is not the last bit
 					if (!rx_bit)								// we expect a 1, 0 is an error
 						rx_sync_state = PH_SYNC_RESET;			// restart preamble detection
 				} else {									// if this is the last bit
 					if (!rx_bit) {								// we expect a 0
 #ifndef TEST
 						radio_frr_read('A', 1);						// read fetched RSSI from FRR
-						ph_rssi = ((int) radio_buffer.data[0] >> 1) - 0x40 - 70;	// calculate dBm: RSSI / 2 - RSSI_COMP - 70
+						ph_rssi = RADIO_RSSI_TO_DBM(radio_buffer.data[0]);	// convert RSSI into dBm
 #endif
 						rx_bit_count = 0;							// reset bit counter
 						ph_state = PH_STATE_PREFETCH;				// next state: start receiving packet
@@ -217,6 +233,13 @@ __interrupt void ph_irq_handler(void)
 
 		case PH_STATE_PREFETCH:								// state: pre-fill receive buffer with 8 bits
 			rx_bit_count++;									// increase bit counter
+
+			if (!RADIO_SIGNAL) {							// if we don't have a stable signal
+				ph_last_error = PH_ERROR_RSSI_DROP;				// report error
+				ph_state = PH_STATE_RESET;						// abort package
+				break;
+			}
+
 			if (rx_bit_count == 8) {						// after 8 bits arrived
 				rx_bit_count = 0;							// reset bit counter
 				rx_one_count = 0;							// reset counter for stuff bits
@@ -230,6 +253,12 @@ __interrupt void ph_irq_handler(void)
 			break;											// do nothing for the first 8 bits to fill buffer
 
 		case PH_STATE_RECEIVE_PACKET:						// state: receiving packet data
+			if (!RADIO_SIGNAL) {							// if we don't have a stable signal
+				ph_last_error = PH_ERROR_RSSI_DROP;				// report error
+				ph_state = PH_STATE_RESET;						// abort package
+				break;
+			}
+
 			rx_bit = rx_bitstream & 0x80;					// extract data bit for processing
 
 			if (rx_one_count == 5) {						// if we expect a stuff-bit..

packet_handler.h

@@ -27,10 +27,10 @@ enum PH_STATE {
 // packet handler errors
 enum PH_ERROR {
 	PH_ERROR_NONE = 0,
-	PH_ERROR_NOSTART,		// no start flag after preamble
 	PH_ERROR_STUFFBIT,		// invalid stuff-bit
 	PH_ERROR_NOEND,			// no end flag after more than 1020 bits, message too long
-	PH_ERROR_CRC			// CRC error
+	PH_ERROR_CRC,			// CRC error
+	PH_ERROR_RSSI_DROP		// signal strength fell below threshold
 };
 
 uint8_t ph_get_state(void);			// get current state of packet handler

radio.c

@@ -20,17 +20,24 @@
 
 #define CMD_NOP						0x00
 #define CMD_PART_INFO				0x01
+#define CMD_POWER_UP				0x02
 #define CMD_FUNC_INFO				0x10
-#define CMD_POWER_UP				0x12
+#define CMD_SET_PROPERTY			0x11
+#define CMD_GET_PROPERTY			0x12
+#define CMD_GPIO_PIN_CONFIG			0x13
+#define CMD_GET_ADC_READING			0x14
 #define CMD_FIFO_INFO				0x15
+#define CMD_PACKET_INFO				0x16
 #define CMD_IRCAL					0x17
+#define CMD_PROTOCOL_CFG			0x18
 #define CMD_GET_INT_STATUS			0x20
 #define CMD_GET_PH_STATUS			0x21
 #define CMD_GET_MODEM_STATUS		0x22
 #define CMD_GET_CHIP_STATUS			0x23
 #define CMD_START_RX				0x32
 #define CMD_REQUEST_DEVICE_STATE	0x33
 #define CMD_CHANGE_STATE			0x34
+#define CMD_RX_HOP					0x36
 #define CMD_READ_CMD_BUFF			0x44
 #define CMD_FRR_A_READ				0x50
 #define CMD_READ_RX_FIFO			0x77
@@ -44,8 +51,8 @@ const uint8_t radio_ircal_sequence_fine[] = { 0x13, 0x10, 0xCA, 0xF0 };
 
 union radio_buffer_u radio_buffer;
 
-void send_command(uint8_t cmd, const uint8_t *send_buffer, uint8_t send_length, uint8_t response_length);
-int receive_result(uint8_t length);
+static void send_command(uint8_t cmd, const uint8_t *send_buffer, uint8_t send_length, uint8_t response_length);
+static int receive_result(uint8_t length);
 
 // configure I/O pins used for radio
 void radio_setup(void)
@@ -102,6 +109,17 @@ void radio_configure(void)
 	return;
 }
 
+// directly set individual radio property
+void radio_set_property(uint8_t prop_group,	uint8_t prop_num, uint8_t value)
+{
+	radio_buffer.data[0] = prop_group;
+	radio_buffer.data[1] = 1;
+	radio_buffer.data[2] = prop_num;
+	radio_buffer.data[3] = value;
+	send_command(CMD_SET_PROPERTY, radio_buffer.data, 4, 0);
+	return;
+}
+
 // invoke radio image rejection self-calibration
 void radio_calibrate_ir(void)
 {

radio.h

@@ -14,7 +14,7 @@
 #define RADIO_GPIO_2		BIT2	// 2.2 configurable, e.g. RX data clock
 #define RADIO_GPIO_3		BIT3	// 2.3 configurable, e.g. RX data
 #define RADIO_SDN			BIT4	// 2.4 chip shutdown, set high for 1us to reset radio, pulled low by 100k resistor
-#define RADIO_NIRQ			BIT5	// 2.5 configurable, e.g. preamble, high when detected (for debug only, use sync word for actual package detection)
+#define RADIO_NIRQ			BIT5	// 2.5 configurable, e.g. CCA, high when RSSI exceeding threshold
 
 #define RADIO_CTS			RADIO_GPIO_1	// when low, chip is busy/not ready
 #ifndef TEST
@@ -23,6 +23,17 @@
 #define RADIO_READY (1)
 #endif
 
+#define RADIO_CCA			RADIO_NIRQ		// when high, signal strength exceeds RSSI threshold
+#ifndef TEST
+#define RADIO_SIGNAL (P2IN & RADIO_CCA)
+#else
+#define RADIO_SIGNAL (1)
+#endif
+
+// convert RSSI to dBm: RSSI / 2 - RSSI_COMP - 70 and vice versa
+#define RADIO_RSSI_TO_DBM(val) (((int) val >> 1) - 0x40 - 70)
+#define RADIO_DBM_TO_RSSI(val) ((val + 70 + 0x40) << 1)
+
 // functions to start up / reset chip
 void radio_setup(void);								// set up MSP430 pins and SPI for interfacing w/ radio
 void radio_configure(void);							// configure radio using radio_config_Si4362.h
@@ -75,6 +86,11 @@ void radio_frr_read(								// read fast read registers, results in radio_buffer
 					uint8_t frr,					// start register 'A', 'B', 'C' or 'D'
 					uint8_t count);					// number of registers to read (1-4)
 
+void radio_set_property(							// directly set individual radio property
+					uint8_t prop_group,				// property group, e.g. 0x20 for MODEM
+					uint8_t prop_num,				// property number, e.g. 0x4a for RSSI threshold
+					uint8_t value);					// property value, e.g. RADIO_DBM_TO_RSSI(-80)
+
 // data structures of various responses, access via radio_buffer.* after calling respective radio_get_* function
 
 struct part_info_s {

radio_config.h

@@ -356,7 +356,7 @@
 // MODEM_RSSI_CONTROL - Selects if the RSSI value is latched, and at what point in the packet it is latched. The Latched RSSI value may be read by a Fast Response Register, or returned by the GET_MODEM_STATUS command. Selects whether the RSSI value is updated every 1*Tb bit period, or whether the RSSI value is averaged over the previous 4*Tb bit periods. Selects if the Latched RSSI value is compared against the MODEM_RSSI_THRESH value, for the purpose of exiting to the RXTIMEOUT_STATE if below threshold.
 */
 //#define RF_MODEM_OOK_CNT1_11 0x11, 0x20, 0x0B, 0x42, 0x84, 0x03, 0xD6, 0x83, 0x00, 0xA4, 0x01, 0x80, 0xFF, 0x0C, 0x02        // 02 = latch RSSI when sync word detected
-#define RF_MODEM_OOK_CNT1_11 0x11, 0x20, 0x0B, 0x42, 0x84, 0x03, 0xD6, 0x83, 0x00, 0xA4, 0x01, 0x80, 0x58, 0x0C, 0x03        // 03 = latch RSSI 4*Tb, RSSI threshold at -100db
+#define RF_MODEM_OOK_CNT1_11 0x11, 0x20, 0x0B, 0x42, 0x84, 0x03, 0xD6, 0x83, 0x00, 0xA4, 0x01, 0x80, 0x58, 0x0C, 0x03        // 03 = latch RSSI 4*Tb, RSSI threshold at -90dBm
 
 /*
 // Set properties: RF_MODEM_RSSI_COMP_1