Handle sequence numbers

This should enable basic retransmission handling.

impl/src/layer2/layer2_rx.c

@@ -13,6 +13,7 @@
 result_t layer2_rx_init(layer2_rx_t *ctx, int tun_fd)
 {
 	ctx->last_acked_seq = 0;
+	ctx->next_expected_seq = 0;
 	ctx->tun_fd = tun_fd;
 	return OK;
 }
@@ -45,6 +46,14 @@ result_t layer2_rx_handle_packet(layer2_rx_t *ctx, const uint8_t *buf, size_t bu
 
 	ctx->last_acked_seq = header.rx_seq_nr;
 
+	if(ctx->next_expected_seq != header.tx_seq_nr) {
+		LOG(LVL_ERR, "Expected sequence number %u, received %u.", ctx->next_expected_seq, header.tx_seq_nr);
+		return ERR_SEQUENCE;
+	}
+
+	ctx->next_expected_seq++;
+	ctx->next_expected_seq &= 0xF;
+
 	size_t header_size = layer2_get_encoded_header_size(&header);
 
 	// extract the payload and forward it to the tun device
@@ -60,6 +69,12 @@ result_t layer2_rx_handle_packet(layer2_rx_t *ctx, const uint8_t *buf, size_t bu
 }
 
 
+uint8_t layer2_rx_get_next_expected_seq(const layer2_rx_t *ctx)
+{
+	return ctx->next_expected_seq;
+}
+
+
 uint8_t layer2_rx_get_last_acked_seq(const layer2_rx_t *ctx)
 {
 	return ctx->last_acked_seq;

impl/src/layer2/layer2_rx.h

@@ -5,6 +5,7 @@
 
 typedef struct {
 	uint8_t last_acked_seq;
+	uint8_t next_expected_seq;
 
 	int tun_fd;
 } layer2_rx_t;
@@ -31,6 +32,10 @@ void layer2_rx_destroy(layer2_rx_t *ctx);
  */
 result_t layer2_rx_handle_packet(layer2_rx_t *ctx, const uint8_t *buf, size_t buf_len);
 
+/*!\brief Return the sequence number expected next by our side.
+ */
+uint8_t layer2_rx_get_next_expected_seq(const layer2_rx_t *ctx);
+
 /*!\brief Return the sequence number expected next by the other side.
  */
 uint8_t layer2_rx_get_last_acked_seq(const layer2_rx_t *ctx);

impl/src/main.c

@@ -46,6 +46,8 @@ static double next_tx_switch_time = 0.0;
 static rx_stats_t m_rx_stats;
 
 static layer2_rx_t l2rx;
+static layer2_tx_t l2tx;
+
 
 static void signal_handler(int signal, siginfo_t *info, void *ctx)
 {
@@ -100,6 +102,7 @@ void cb_rx(rx_evt_t evt, const struct layer1_rx_s *rx, uint8_t *packet_data, siz
 			result_t result = layer2_rx_handle_packet(&l2rx, packet_data, packet_len);
 			switch(result) {
 				case OK:
+					layer2_tx_handle_ack(&l2tx, layer2_rx_get_last_acked_seq(&l2rx));
 					m_rx_stats.successful_decodes++;
 					break;
 
@@ -108,6 +111,10 @@ void cb_rx(rx_evt_t evt, const struct layer1_rx_s *rx, uint8_t *packet_data, siz
 					m_rx_stats.failed_decodes++;
 					break;
 
+				case ERR_SEQUENCE:
+					LOG(LVL_ERR, "Packet not in the expected sequence.");
+					break;
+
 				default: // all other errors
 					LOG(LVL_ERR, "layer2_rx_handle_packet() returned error code %u.", result);
 					break;
@@ -149,8 +156,6 @@ int main(int argc, char **argv)
 	layer1_tx_t tx;
 	layer1_rx_t rx;
 
-	layer2_tx_t l2tx;
-
 	sdr_ctx_t   sdr;
 
 	// initialize the console logger
@@ -248,7 +253,9 @@ int main(int argc, char **argv)
 					uint8_t packet_buf[2048];
 					size_t packet_size;
 
-					packet_size = layer2_tx_encode_next_packet(&l2tx, 0 /* FIXME */, packet_buf, sizeof(packet_buf));
+					packet_size = layer2_tx_encode_next_packet(&l2tx,
+							layer2_rx_get_next_expected_seq(&l2rx),
+							packet_buf, sizeof(packet_buf));
 
 					if(packet_size == 0) {
 						// no more packets available

impl/src/results.h

@@ -14,6 +14,7 @@ typedef enum {
 	ERR_SOAPY,          // an error occurred in the SoapySDR library.
 	ERR_SDR,            // an error occurred in the SDR interface.
 	ERR_INTEGRITY,      // an integrity check failed (e.g. CRC of received packet is wrong)
+	ERR_SEQUENCE,       // an unexpected packet was received
 } result_t;
 
 #ifdef DEBUG_LIQUID