decoding WIP

2 files changed, 79 insertions, 18 deletions

diff --git a/controller/fw/src/dsss_demod.c b/controller/fw/src/dsss_demod.c
index cc1c34e..1cad6f8 100644
--- a/controller/fw/src/dsss_demod.c
+++ b/controller/fw/src/dsss_demod.c
@@ -46,17 +46,16 @@ void debug_print_vector(const char *name, size_t len, const float *data, size_t
 #endif
 
 #ifdef SIMULATION
-void dsss_demod_step(struct dsss_demod_state *st, float new_value, size_t sim_pos, int record_channel) {
+void dsss_demod_step(struct dsss_demod_state *st, float new_value, uint64_t ts, int record_channel) {
     bool debug = (record_channel == -1)
-        && (sim_pos > 1000)
-        && (sim_pos % DSSS_CORRELATION_LENGTH == DSSS_CORRELATION_LENGTH-1);
+        && (ts > 1000)
+        && (ts % DSSS_CORRELATION_LENGTH == DSSS_CORRELATION_LENGTH-1);
 
-    if (debug) DEBUG_PRINT("Iteration %zd: signal=%f", sim_pos, new_value);
+    if (debug) DEBUG_PRINT("Iteration %zd: signal=%f", ts, new_value);
 #else
 void dsss_demod_step(struct dsss_demod_state *st, float new_value) {
 #endif
 
-    //const float peak_group_threshold = 0.05 * DSSS_CORRELATION_LENGTH;
     //const float hole_patching_threshold = 0.01 * DSSS_CORRELATION_LENGTH;
 
     st->signal[st->signal_wpos] = new_value;
@@ -89,7 +88,7 @@ void dsss_demod_step(struct dsss_demod_state *st, float new_value) {
 
     float max_val = st->group.max;
     int max_ch = st->group.max_ch;
-    int max_idx = st->group.max_idx + 1;
+    int max_ts = st->group.max_ts;
     bool found = false;
     for (size_t i=0; i<DSSS_GOLD_CODE_COUNT; i++) {
         float val = cwt[i] / avg[i];
@@ -100,7 +99,7 @@ void dsss_demod_step(struct dsss_demod_state *st, float new_value) {
         if (fabs(val) > fabs(max_val)) {
             max_val = val;
             max_ch = i;
-            max_idx = st->group.len;
+            max_ts = ts;
         }
     }
 
@@ -109,7 +108,7 @@ void dsss_demod_step(struct dsss_demod_state *st, float new_value) {
         st->group.len++;
         st->group.max = max_val;
         st->group.max_ch = max_ch;
-        st->group.max_idx = max_idx;
+        st->group.max_ts = max_ts;
         return;
     }
     
@@ -120,15 +119,60 @@ void dsss_demod_step(struct dsss_demod_state *st, float new_value) {
     /* A group ended. Process result. */
     if (record_channel == -1)
         DEBUG_PRINT("GROUP FOUND: %8d len=%3d max=%f ch=%d offx=%d",
-                sim_pos, st->group.len, st->group.max, st->group.max_ch, st->group.max_idx);
+                ts, st->group.len, st->group.max, st->group.max_ch, st->group.max_ts);
 
     /* reset grouping state */
     st->group.len = 0;
-    st->group.max_idx = 0;
+    st->group.max_ts = 0;
     st->group.max_ch = 0;
     st->group.max = 0.0f;
 }
 
+float score_group(const struct group *g, uint64_t ts) {
+    return fabs(g->max); /* Possibly at time penalty 1/(ts-max_ts) later */
+}
+
+ssize_t group_cache_insertion_index(const struct group *g, const struct group *cache, size_t cache_size, uint64_t ts) {
+    float min_score = INFINITY;
+    ssize_t min_idx = -1;
+    for (size_t i=0; i<cache_size; i++) {
+        /* If we find an empty or expired entry, use that */
+        if (cache[i].max_ts == 0 || ts - cache[i].max_ts > group_cache_expiration)
+            return i;
+
+        /* Otherwise check weakest entry */
+        float score = score_group(&cache[i]);
+        if (score < min_score) {
+            min_idx = i;
+            min_score = score;
+        }
+    }
+
+    /* Return weakest group if weaker than candidate */
+    if (min_score < score_group(g))
+        return min_idx;
+
+    return -1;
+}
+
+void group_received(struct dsss_demod_state *st, uint64_t ts) {
+    /* TODO make these constants configurable from Makefile */
+    const uint64_t group_cache_expiration = DSSS_CORRELATION_LENGTH * DSSS_GROUP_CACHE_SIZE;
+
+    /* Insert into group cache if space is available or there is a weaker entry to replace */
+    ssize_t found = group_cache_insertion_index(&st->group, st->group_cache, DSSS_GROUP_CACHE_SIZE);
+    if (!found)
+        return; /* Nothing changed */
+    st->group_cache[found] = st->group;
+
+    float mean_phase = 0.0;
+    for (size_t i=0; i<DSSS_GROUP_CACHE_SIZE; i++)
+        mean_phase += (st->group_cache[i].max_ts) % DSSS_CORRELATION_LENGTH;
+    mean_phase /= DSSS_GROUP_CACHE_SIZE;
+
+    
+}
+
 float run_iir(const float x, const int order, const struct iir_biquad q[order], struct iir_biquad_state st[order]) {
     float intermediate = x;
     for (int i=0; i<(order+1)/2; i++)
diff --git a/controller/fw/src/dsss_demod.h b/controller/fw/src/dsss_demod.h
index b6947bc..30ec3f7 100644
--- a/controller/fw/src/dsss_demod.h
+++ b/controller/fw/src/dsss_demod.h
@@ -5,6 +5,8 @@
 #define DSSS_GOLD_CODE_COUNT    ((1<<DSSS_GOLD_CODE_NBITS) + 1)
 #define DSSS_CORRELATION_LENGTH (DSSS_GOLD_CODE_LENGTH * DSSS_DECIMATION)
 
+#define PAYLOAD_DATA_BYTE ((PAYLOAD_DATA_BIT+7)/8)
+
 struct iir_biquad {
     float a[2];
     float b[3];
@@ -18,6 +20,24 @@ struct cwt_iir_filter_state {
     struct iir_biquad_state st[3];
 };
 
+struct {
+    int len; /* length of group in samples */
+    float max; /* signed value of largest peak in group on any channel */
+    uint64_t max_ts; /* absolute position of above peak */
+    int max_ch; /* channel (gold sequence index) of above peak */
+} group;
+
+struct decoder_state {
+    int last_phase;
+    int candidate_phase;
+
+    float last_score;
+    float candidate_score;
+
+    uint8_t data[PAYLOAD_DATA_BYTE]; 
+    int data_pos;
+};
+
 struct dsss_demod_state {
     float signal[DSSS_CORRELATION_LENGTH];
     size_t signal_wpos;
@@ -27,18 +47,15 @@ struct dsss_demod_state {
 
     struct cwt_iir_filter_state cwt_filter[DSSS_GOLD_CODE_COUNT];
 
-    struct {
-        int len; /* length of group in samples */
-        float max; /* signed value of largest peak in group on any channel */
-        int max_idx; /* position of above peak counted from start of group */
-        int max_ch; /* channel (gold sequence index) of above peak */
-    } group;
+    struct group group;
+
+    struct group group_cache[DSSS_GROUP_CACHE_SIZE];
 };
 
 #ifdef SIMULATION
-void dsss_demod_step(struct dsss_demod_state *st, float new_value, size_t sim_pos, int record_channel);
+void dsss_demod_step(struct dsss_demod_state *st, float new_value, uint64_t ts, int record_channel);
 #else /* SIMULATION */
-void dsss_demod_step(struct dsss_demod_state *st, float new_value);
+void dsss_demod_step(struct dsss_demod_state *st, float new_value, uint64_t ts);
 #endif /* SIMULATION */
 
 #endif /* __DSSS_DEMOD_H__ */