From 91facbf6999542d0cbe7c06337d77d2194a5e90a Mon Sep 17 00:00:00 2001
From: Thomas Kolb <cfr34k-git@tkolb.de>
Date: Tue, 28 May 2024 19:55:21 +0200
Subject: [PATCH] rx: reset internal state when restarting after a transmission

---
 impl/src/layer1/correlator.c |  9 +++++++++
 impl/src/layer1/correlator.h | 10 ++++++++++
 impl/src/layer1/rx.c         | 18 ++++++++++++++++++
 impl/src/layer1/rx.h         | 18 +++++++++++++++++-
 impl/src/main.c              |  1 +
 5 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/impl/src/layer1/correlator.c b/impl/src/layer1/correlator.c
index f1c5426..1340313 100644
--- a/impl/src/layer1/correlator.c
+++ b/impl/src/layer1/correlator.c
@@ -76,6 +76,15 @@ void correlator_free(correlator_ctx_t *ctx)
 	ctx->search_sequence_len = 0;
 }
 
+void correlator_reset(correlator_ctx_t *ctx)
+{
+	// Clear the history buffer
+	memset(ctx->input_history, 0, ctx->buffer_size * sizeof(ctx->input_history[0]));
+
+	// start writing from the beginning
+	ctx->history_ptr = 0;
+}
+
 
 float complex correlator_step(correlator_ctx_t *ctx, float complex sample)
 {
diff --git a/impl/src/layer1/correlator.h b/impl/src/layer1/correlator.h
index ef38293..65144d1 100644
--- a/impl/src/layer1/correlator.h
+++ b/impl/src/layer1/correlator.h
@@ -67,6 +67,16 @@ bool correlator_init(correlator_ctx_t *ctx, const float complex *search_seq, siz
  */
 void correlator_free(correlator_ctx_t *ctx);
 
+/*!
+ * \brief Reset a correlator.
+ *
+ * \details
+ * Erases all data in the history buffer and starts writing from the beginning.
+ *
+ * \param ctx          The correlator context to reset.
+ */
+void correlator_reset(correlator_ctx_t *ctx);
+
 /*!
  * \brief Process one sample in the correlator.
  *
diff --git a/impl/src/layer1/rx.c b/impl/src/layer1/rx.c
index 43e09db..1b0e843 100644
--- a/impl/src/layer1/rx.c
+++ b/impl/src/layer1/rx.c
@@ -600,6 +600,24 @@ result_t layer1_rx_shutdown(layer1_rx_t *rx)
 }
 
 
+result_t layer1_rx_reset(layer1_rx_t *rx)
+{
+	// reset the state machine
+	rx->state = RX_STATE_ACQUISITION;
+
+	// reset the correlator (to avoid spurious preamble detection)
+	correlator_reset(&rx->preamble_correlator);
+
+	// reset symbol synchronizer
+	symsync_crcf_reset(rx->symsync);
+
+	// drop partial debug info
+	reset_packet_debug_info(rx);
+
+	return OK;
+}
+
+
 bool layer1_rx_is_busy(const layer1_rx_t *rx)
 {
 	return is_squelch_open(rx);
diff --git a/impl/src/layer1/rx.h b/impl/src/layer1/rx.h
index 6564592..7b315b6 100644
--- a/impl/src/layer1/rx.h
+++ b/impl/src/layer1/rx.h
@@ -114,7 +114,7 @@ result_t layer1_rx_shutdown(layer1_rx_t *rx);
  * \param rx             Pointer to the receiver context.
  * \param samples        Pointer to the samples to process.
  * \param sample_count   Number of samples to process.
- * \returns              The result of the shutdown.
+ * \returns              The result of the sample processing.
  */
 result_t layer1_rx_process(layer1_rx_t *rx, const float complex *samples, size_t sample_count);
 
@@ -142,4 +142,20 @@ bool layer1_rx_is_busy(const layer1_rx_t *rx);
  */
 float layer1_rx_get_coarse_carrier_frequency(const layer1_rx_t *rx);
 
+
+/*!
+ * \brief Reset the receiver.
+ *
+ * This ensures that the receiver can lock on to newly received packets in a
+ * defined way. The following submodules are reset:
+ *
+ * - Correlator
+ * - RX state machine
+ * - Symbol synchronization
+ *
+ * \param rx             Pointer to the receiver context.
+ * \returns              The result of the reset.
+ */
+result_t layer1_rx_reset(layer1_rx_t *rx);
+
 #endif // LAYER1_RX_H
diff --git a/impl/src/main.c b/impl/src/main.c
index 0eb265f..4a86f71 100644
--- a/impl/src/main.c
+++ b/impl/src/main.c
@@ -317,6 +317,7 @@ int main(int argc, char **argv)
 			} else if(on_air) { // ret == 0
 				fprintf(stderr, "TX -> RX\n");
 				RESULT_CHECK(sdr_flush_tx_buffer(&sdr));
+				RESULT_CHECK(layer1_rx_reset(&rx));
 
 				RESULT_CHECK(sdr_stop_tx(&sdr));
 				RESULT_CHECK(sdr_start_rx(&sdr));