update notes

diff --git a/notes.txt b/notes.txt
index 5c336782adcdb18cee9a79b8444f5351790080bd..882dbc377f1b4f365fafcbe2109596e9c2c9430a 100644 (file)
--- a/notes.txt
+++ b/notes.txt
@@ -471,3 +471,33 @@ mainboard > rc_proto_hello wing 25 1000 0123456789
 mainboard > rc_proto_hello wing 25 1000 01234567890123456789
   898/1000
   898/1000
+
+
+Latency
+===============
+
+the ECHO command contains a timestamp, allowing latency measurement.
+the structure is a but larger than a HELLO message.
+
+mainboard > rc_proto_stats reset
+mainboard > rc_proto_echo wing 50 50 x
+mainboard > rc_proto_stats show
+  echo_ans_latency_ms: 80
+
+mainboard > rc_proto_stats reset
+mainboard > rc_proto_echo wing 50 50 0123456789
+mainboard > rc_proto_stats show
+  echo_ans_latency_ms: 95
+
+mainboard > rc_proto_stats reset
+mainboard > rc_proto_echo wing 50 50 01234567890123456789
+mainboard > rc_proto_stats show
+  echo_ans_latency_ms: 125
+
+The latency is probably small enough for our RC application, but it is
+not as small as expected.
+
+serial from uc to xbee at 57600 = ~3ms for 20 bytes
+radio rate is 24000: ~6.66ms for 20 bytes
+
+the progression of latency is not linear.