Radio link improvements

- improve latency by only allowing 3*MTU packets in the firmware buffer
- measure total buffer size (as highest remaining seen)

radio_link.c

@@ -124,9 +124,8 @@ struct radio_link_state{
   int remote_rssi;
   // estimated firmware buffer space
   int32_t remaining_space;
+  int32_t total_space;
   
-  // next serial write
-  uint64_t next_tx_allowed;
   // partially sent packet
   struct overlay_buffer *tx_packet;
   
@@ -169,7 +168,8 @@ int radio_link_free(struct overlay_interface *interface)
 int radio_link_init(struct overlay_interface *interface)
 {
   interface->radio_link_state = emalloc_zero(sizeof(struct radio_link_state));
-  interface->radio_link_state->remaining_space = 512;
+  interface->radio_link_state->remaining_space = 256;
+  interface->radio_link_state->total_space = 256;  
   return 0;
 }
 
@@ -265,10 +265,6 @@ int radio_link_tx(struct overlay_interface *interface)
     now = gettime_ms();
     
     if (link_state->tx_bytes){
-      if (link_state->next_tx_allowed > now){
-	interface->alarm.alarm = link_state->next_tx_allowed;
-	break;
-      }
       int bytes = link_state->tx_bytes;
       if (bytes > link_state->remaining_space){
 	bytes = link_state->remaining_space;
@@ -289,6 +285,8 @@ int radio_link_tx(struct overlay_interface *interface)
 	link_state->tx_pos+=written;
       else
 	link_state->tx_pos=0;
+      if (config.debug.packetradio)
+	INFOF("Radio packet TX wrote %d, remaining %d", written, link_state->remaining_space);
       continue;
     }
   
@@ -456,18 +454,33 @@ int radio_link_decode(struct overlay_interface *interface, const uint8_t *buffer
 	  // we can assume that radio status packets arrive without corruption
 	  state->radio_rssi=state->radio_header[2];//(1.0*payload[10]-payload[13])/1.9;
 	  state->remote_rssi=state->radio_header[3];//(1.0*payload[11] - payload[14])/1.9;
-	  state->remaining_space = ((state->radio_header[7]<<8) | state->radio_header[6]) - 64;
-	  if (state->remaining_space>=LINK_MTU){
-	    state->next_tx_allowed = gettime_ms();
-	  }
-	    
+	  state->remaining_space = ((state->radio_header[7]<<8) | state->radio_header[6]);
+	  
+	  // track the actual buffer space
+	  if (state->total_space < state->remaining_space)
+	    state->total_space = state->remaining_space;
+	  
 	  if (config.debug.packetradio)
-	    INFOF("RX len = %02x, rssi = %+ddB, remote rssi = %+ddB, buffer space = %d",
+	    INFOF("Radio packet RX len = %02x, rssi = %+ddB, remote rssi = %+ddB, buffer space = %d (of %d)",
 		  state->radio_header[5],
 		  state->radio_rssi,
 		  state->remote_rssi,
-		  state->remaining_space);
-		  
+		  state->remaining_space,
+		  state->total_space);
+	  
+	  // reserve some bytes to allow for rtt lag and hope that's enough
+	  if (state->remaining_space<64)
+	    state->remaining_space=0;
+	  else
+	    state->remaining_space-=64;
+	    
+	  if (state->total_space > 3*LINK_MTU){
+	    if (state->remaining_space < (state->total_space - 3*LINK_MTU))
+	      state->remaining_space = 0;
+	    else
+	      state->remaining_space -= (state->total_space - 3*LINK_MTU);
+	  }
+	  
 	  if (state->radio_header[5])
 	    state->mode=MODE_PACKET;
 	}else if (config.debug.radio_link)

tests/rhizomeprotocol

@@ -702,7 +702,7 @@ start_radio_instance() {
       set debug.rhizome_tx on \
       set debug.rhizome_rx on \
       set debug.throttling on \
-      set debug.radio_link on \
+      set debug.packetradio on \
       set rhizome.advertise.interval 5000 \
       set rhizome.rhizome_mdp_block_size 375 \
       set log.console.level debug \

tests/routing

@@ -261,7 +261,7 @@ test_slip_encoding() {
    executeOk_servald test slip --seed=1 --iterations=2000
 }
 start_fakeradio() {
-   $servald_build_root/fakeradio 4 1 > "$SERVALD_VAR/radioout" 2> "$SERVALD_VAR/radioerr" &
+   $servald_build_root/fakeradio 4 0.8 > "$SERVALD_VAR/radioout" 2> "$SERVALD_VAR/radioerr" &
    FAKERADIO_PID=$!
    wait_until $GREP "^right:" "$SERVALD_VAR/radioout"
    local _line=`head "$SERVALD_VAR/radioout" -n 1`
@@ -299,7 +299,7 @@ test_simulate_extender() {
    wait_until path_exists +A +B
    wait_until path_exists +B +A
    set_instance +A
-   executeOk_servald mdp ping --timeout=3 $SIDB 1
+   executeOk_servald mdp ping --interval=0.3 --timeout=5 $SIDB 100
    tfw_cat --stdout --stderr
 }
 teardown_simulate_extender() {