Support framed FSK Manchester decoding compatible with Si4320/RFM01

Detection in pulse_analyzer() is left to a separate commit because it's
ugly and wants separate review.

include/pulse_demod.h

@@ -115,6 +115,32 @@ int pulse_demod_pwm_ternary(const pulse_data_t *pulses, struct protocol_state *d
 /// @return number of events processed
 int pulse_demod_manchester_zerobit(const pulse_data_t *pulses, struct protocol_state *device);
 
+/// Demodulate a Manchester encoded signal with preamble and postamble as used by HopeRF RFMxx modules
+///
+/// Each frame has a preamble of three high-level periods, followed by three low-level
+/// periods (which we presume might be four, if the first data bit is a 1. Although
+/// we actually have yet to see a transmission where the first data bit is a 1).
+/// The end of frame is marked by staying at the same level (high or low
+/// depending on the value of the last data bit) for two further periods.
+///
+/// +-----------+           +---+       +-----------+  high frequency
+/// |           |           |   |       |
+/// |           |           |   |       |
+/// +           +-----------+   +-------+              low frequency
+///
+/// ^   ^   ^   ^   ^   ^   ^   ^   ^   ^   ^   ^   ^
+/// |  preamble | preamble  |   0   |   1   |  end      translates as
+///
+/// Clock is recovered from the data based on pulse width. When time since last bit is more
+/// than 1.5 times the clock half period (short_width) it is declared a data edge where:
+/// - Rising edge means bit = 1
+/// - Falling edge means bit = 0
+/// @param device->short_limit: Nominal width of clock half period [samples]
+/// @param device->long_limit:  Not used
+/// @param device->reset_limit: Not used
+/// @return number of events processed
+int pulse_demod_manchester_framed(const pulse_data_t *pulses, struct protocol_state *device);
+
 
 /// No level shift within the clock cycle translates to a logic 0
 /// One level shift within the clock cycle translates to a logic 1

include/rtl_433.h

@@ -43,10 +43,10 @@
 #define	OOK_PULSE_PWM_RAW		7			// Pulse Width Modulation. Short pulses = 1, Long = 0
 #define	OOK_PULSE_PWM_TERNARY	8			// Pulse Width Modulation with three widths: Sync, 0, 1. Sync determined by argument
 #define	OOK_PULSE_CLOCK_BITS		9			// Level shift within the clock cycle.
-
 #define	FSK_DEMOD_MIN_VAL		16			// Dummy. FSK demodulation must start at this value
 #define	FSK_PULSE_PCM			16			// FSK, Pulse Code Modulation
 #define	FSK_PULSE_PWM_RAW		17			// FSK, Pulse Width Modulation. Short pulses = 1, Long = 0
+#define	FSK_PULSE_MANCHESTER_FRAMED 18		// FSK, Framed Manchester encoding as used by HopeRF RFMxx modules.
 
 extern int debug_output;
 

src/pulse_demod.c

@@ -278,6 +278,82 @@ int pulse_demod_manchester_zerobit(const pulse_data_t *pulses, struct protocol_s
 	return events;
 }
 
+int pulse_demod_manchester_framed(const pulse_data_t *pulses, struct protocol_state *device) {
+	int events = 0;
+	unsigned time_since_last = -1;
+	bitbuffer_t bits = {0};
+
+	for(unsigned n = 0; n < pulses->num_pulses; ++n) {
+		if (time_since_last == (unsigned)-1) {
+			// Waiting for start-of-frame pulse (HHH)
+			if (pulses->pulse[0] < (unsigned)(device->short_limit*5)/2)
+				continue;
+			// First gap must be 3 or 4 periods.
+			if (pulses->gap[0] < (unsigned)(device->short_limit * 5)/2 ||
+			    pulses->gap[0] > (unsigned)(device->short_limit * 9)/2)
+				continue;
+
+			// If first gap is three periods (LLL), the first bit
+			// first bit is a 0 (HL) and will be counted on the
+			// next pulse. If first gap is four periods (LLLL),
+			// the first bit is a 1 (LH) and must be counted now.
+			if (pulses->gap[0] > (unsigned)(device->short_limit*7)/2) {
+				time_since_last = 0;
+				bitbuffer_add_bit(&bits, 1);
+			} else
+				time_since_last = device->short_limit;
+			continue;
+		}
+
+		// Falling edge is on end of pulse
+		if(!time_since_last && pulses->pulse[n] > (unsigned)(device->short_limit * 5)/2) {
+			// End of frame */
+		end_of_frame:
+			if (device->callback) {
+				events += device->callback(&bits);
+			}
+			// Debug printout
+			if(!device->callback || (debug_output && events > 0)) {
+				fprintf(stderr, "pulse_demod_manchester_zerobit(): %s \n", device->name);
+				bitbuffer_print(&bits);
+			}
+		reset:
+			bitbuffer_clear(&bits);
+			time_since_last = -1;
+			continue;
+		}
+
+		// If there's no edge where we need one...
+		if(pulses->pulse[n] + time_since_last > (unsigned)(device->short_limit * 5)/2)
+			goto reset;
+
+		if(pulses->pulse[n] + time_since_last > (unsigned)(device->short_limit * 3)/2) {
+			// Last bit was recorded more than short_limit*1.5 samples ago 
+			// so this pulse start must be a data edge (falling data edge means bit = 0)
+			bitbuffer_add_bit(&bits, 0);
+			time_since_last = 0;
+		} else {
+			time_since_last += pulses->pulse[n];
+		}
+
+		if(!time_since_last && pulses->gap[n] > (unsigned)(device->short_limit * 5)/2)
+			goto end_of_frame;
+		if(pulses->gap[n] + time_since_last > (unsigned)(device->short_limit * 5)/2)
+			goto reset;
+
+		// Rising edge is on end of gap
+		if(pulses->gap[n] + time_since_last > (unsigned)(device->short_limit * 3)/2) {
+			// Last bit was recorded more than short_limit*1.5 samples ago 
+			// so this pulse end is a data edge (rising data edge means bit = 1) 
+			bitbuffer_add_bit(&bits, 1);
+			time_since_last = 0;
+		} else {
+			time_since_last += pulses->gap[n];
+		}
+	}
+	return events;
+}
+
 int pulse_demod_clock_bits(const pulse_data_t *pulses, struct protocol_state *device) {
    unsigned int symbol[PD_MAX_PULSES * 2];
    unsigned int n;

src/pulse_detect.c

@@ -435,6 +435,9 @@ void pulse_analyzer(pulse_data_t *data)
 			case OOK_PULSE_MANCHESTER_ZEROBIT:
 				pulse_demod_manchester_zerobit(data, &device);
 				break;
+			case FSK_PULSE_MANCHESTER_FRAMED:
+				pulse_demod_manchester_framed(data, &device);
+				break;
 			default:
 				fprintf(stderr, "Unsupported\n");
 		}

src/rtl_433.c

@@ -636,6 +636,7 @@ static void rtlsdr_callback(unsigned char *iq_buf, uint32_t len, void *ctx) {
 				case OOK_PULSE_CLOCK_BITS:
 				case FSK_PULSE_PCM:
 				case FSK_PULSE_PWM_RAW:
+				case FSK_PULSE_MANCHESTER_FRAMED:
 					break;
 				default:
 					fprintf(stderr, "Unknown modulation %d in protocol!\n", demod->r_devs[i]->modulation);
@@ -676,6 +677,7 @@ static void rtlsdr_callback(unsigned char *iq_buf, uint32_t len, void *ctx) {
 						// FSK decoders
 						case FSK_PULSE_PCM:
 						case FSK_PULSE_PWM_RAW:
+						case FSK_PULSE_MANCHESTER_FRAMED:
 							break;
 						default:
 							fprintf(stderr, "Unknown modulation %d in protocol!\n", demod->r_devs[i]->modulation);
@@ -703,6 +705,9 @@ static void rtlsdr_callback(unsigned char *iq_buf, uint32_t len, void *ctx) {
 						case FSK_PULSE_PWM_RAW:
 							pulse_demod_pwm(&demod->fsk_pulse_data, demod->r_devs[i]);
 							break;
+						case FSK_PULSE_MANCHESTER_FRAMED:
+							pulse_demod_manchester_framed(&demod->fsk_pulse_data, demod->r_devs[i]);
+							break;
 						default:
 							fprintf(stderr, "Unknown modulation %d in protocol!\n", demod->r_devs[i]->modulation);
 					}