client: Explain the exponential re-send delay

diff --git a/client/config.c b/client/config.c
index 83a3eb3e9381e052353067dbab570b6a12094615..d3006c786b97712383e5a08d6bca5b0caf91ad14 100644 (file)
--- a/client/config.c
+++ b/client/config.c
@@ -22,7 +22,29 @@ const uint config_button_pin = 18;
  * times in short succession.  (We also use this to de-bounce. :) */
 const u32_t config_minimum_seconds_between_button_presses = 1;
 
-/* Send each report multiple times. */
+/* Send each report multiple times. Re-sends are sent with exponential delay:
+ *   #1 sent immediately
+ *   #2 after 1 seconds
+ *   #3 after 2 seconds
+ *   #4 after 4 seconds
+ *   #5 after 8 seconds
+ *   ...
+ *   #11 after 8 minutes
+ *   #12 after 17 minutes
+ *   #13 after 34 minutes
+ *   #14 after 68 minutes
+ *   #15 after 2 hours
+ *   #16 after 4 hours
+ *   #17 after 9 hours
+ *   etc.
+ * This provides some robustness against network outages, automatically
+ * replaying the log periodically to be collected after connectivity
+ * is restored.
+ *
+ * Values above 17 are currently not recommended because the current
+ * wire format uses a 16-bit field for a duration in seconds, which wraps
+ * at 18 hours.
+ *   */
 const uint config_resend_count = 5;
 
 /* These control the size of the per-send-count press queues.

diff --git a/client/config.h b/client/config.h
index 2ffce683b52358cce8c605ad37feed37188c5e1a..8d23169c2d2701fd7a53627f0609b8aa5a29731e 100644 (file)
--- a/client/config.h
+++ b/client/config.h
@@ -42,7 +42,29 @@ extern const uint config_button_pin;
  * times in short succession.  (We also use this to de-bounce. :) */
 extern const u32_t config_minimum_seconds_between_button_presses;
 
-/* Send each report multiple times. */
+/* Send each report multiple times. Re-sends are sent with exponential delay:
+ *   #1 sent immediately
+ *   #2 after 1 seconds
+ *   #3 after 2 seconds
+ *   #4 after 4 seconds
+ *   #5 after 8 seconds
+ *   ...
+ *   #11 after 8 minutes
+ *   #12 after 17 minutes
+ *   #13 after 34 minutes
+ *   #14 after 68 minutes
+ *   #15 after 2 hours
+ *   #16 after 4 hours
+ *   #17 after 9 hours
+ *   etc.
+ * This provides some robustness against network outages, automatically
+ * replaying the log periodically to be collected after connectivity
+ * is restored.
+ *
+ * Values above 17 are currently not recommended because the current
+ * wire format uses a 16-bit field for a duration in seconds, which wraps
+ * at 18 hours.
+ *   */
 extern const uint config_resend_count;
 
 /* These control the size of the per-send-count press queues.