fixing rssi=0 S1 mode; rssi filtering done right again

README.md

@@ -69,7 +69,7 @@ The output data is semicolon separated and the meaning of the columns are:
 
 `MODE;CRC_OK;3OUTOF6OK;TIMESTAMP;PACKET_RSSI;CURRENT_RSSI;LINK_LAYER_IDENT_NO;DATAGRAM_WITHOUT_CRC_BYTES.`
 
-3OUTOF6OK is only relevant for T1 and can be ignored for C1 (always set to 1).
+3OUTOF6OK is only relevant for T1 and can be ignored for C1 and S1 (always set to 1).
 
    Bugfixing
    -----
@@ -81,6 +81,8 @@ L(ength) field from C1 mode B datagrams does not include CRC bytes anymore: L fi
 
 Significantly improved C1 receiver quality. Sad, but in the low-pass-filter was a bug: the stopband edge frequency was specified as 10kHz instead of 110kHz. I have changed the latter to 160kHz and recalculated filter coefficients.
 
+Packet rssi value fixed for S1 mode (was always 0): thanks to alalons.
+
    Improvements
    -----
 A new method for picking datagrams out of the bit stream that _could_ probably better perform in C1 mode has been implemented.
@@ -106,15 +108,15 @@ time2 clock recovery method has to be activated in this case (it's active by def
 Last but not least, you can try to receive all datagrams (S1, T1, C1) _simultaneously_:
  * rtl_sdr -f 868.7M -s 1600000 - 2>/dev/null | build/rtl_wmbus -s
 
-Notice in the last line
+Notice in the last line:
  * "-s": which is needed to inform rtl_wmbus about required frequency translation
- * "868.7M": the new frequency to receive at.
+ * "868.7M": the new frequency to receive at
 
 rtl_wmbus will then shift all frequencies
  * by 250kHz to new center frequency at 868.95Mhz (T1 and C1)
  * by 400kHz to new center frequency at 868.3Mhz (S1)
 
-I have tested this so far and can confirm that it works for T1/C1, but can't test for S1 as I have no such meter.
+I have tested this so far and can confirm that it works for T1/C1 and S1. Thanks to alalons for providing me with bitstreams!
 
   License
   -------

rtl_wmbus.c

@@ -332,7 +332,7 @@ static inline float lp_fir_butter_800kHz_32kHz_36kHz(float sample)
     return firf(sample, &filter);
 }
 
-static float rssi_filter(float sample)
+static float rssi_filter_t1_c1(float sample)
 {
     static float old_sample;
 
@@ -343,6 +343,16 @@ static float rssi_filter(float sample)
     return old_sample;
 }
 
+static float rssi_filter_s1(float sample)
+{
+    static float old_sample;
+
+#define ALPHA 0.6789f
+    old_sample = ALPHA*sample + (1.0f - ALPHA)*old_sample;
+#undef ALPHA
+
+    return old_sample;
+}
 
 static inline float polar_discriminator_t1_c1(float i, float q)
 {
@@ -838,10 +848,10 @@ int main(int argc, char *argv[])
             // We are using one simple filter to rssi value in order to
             // prevent unexpected "splashes" in signal power.
             float rssi_t1_c1 = sqrtf(i_t1_c1*i_t1_c1 + q_t1_c1*q_t1_c1);
-            rssi_t1_c1 = rssi_filter(rssi_t1_c1); // comment out, if rssi filtering is unwanted
+            rssi_t1_c1 = rssi_filter_t1_c1(rssi_t1_c1); // comment out, if rssi filtering is unwanted
 
             float rssi_s1 = sqrtf(i_s1*i_s1 + q_s1*q_s1);
-            rssi_s1 = rssi_filter(rssi_s1); // comment out, if rssi filtering is unwanted
+            rssi_s1 = rssi_filter_s1(rssi_s1); // comment out, if rssi filtering is unwanted
 #if defined(USE_MOVING_AVERAGE)
             // If using moving average, we would have multiples of I- and Q- signal components.
             rssi_t1_c1 /= opts_decimation_rate;

s1_packet_decoder.h

@@ -172,6 +172,7 @@ static void s1_rx_bit2(unsigned bit, struct s1_packet_decoder_work *decoder)
 static void s1_rx_first_lfield_bit(unsigned bit, struct s1_packet_decoder_work *decoder)
 {
     decoder->byte = (bit & PACKET_DATABIT_MASK);
+    decoder->packet_rssi = decoder->current_rssi;
 }
 
 static void s1_rx_last_lfield_bit(unsigned bit, struct s1_packet_decoder_work *decoder)