client: Exponential backoff resend intervals

[tattlekey] / client / tattlekey.c

diff --git a/client/tattlekey.c b/client/tattlekey.c
index 78d1dcfd8925c576b362d6fa0d20e09f7686de54..c38de126d50245cd3a9ba08d128e170b6c23d75c 100644 (file)
--- a/client/tattlekey.c
+++ b/client/tattlekey.c
@@ -1,5 +1,6 @@
 #include "pico/cyw43_arch.h"
 #include "pico/stdlib.h"
+#include "pico/util/pheap.h"
 #include "pico/util/queue.h"
 
 #include "blink.h"
@@ -13,6 +14,16 @@ typedef struct {
   u8_t send_count;
 } send_t;
 
+uint32_t next_send(send_t *s) {
+  return s->timestamp + (1 << s->send_count) - 1;
+}
+
+bool next_send_less_than(void *user_data, pheap_node_id_t a,
+                         pheap_node_id_t b) {
+  send_t *sends = (send_t *)user_data;
+  return next_send(&sends[a]) < next_send(&sends[b]);
+}
+
 enum event_type { BUTTONPRESS, SEND };
 typedef struct {
   enum event_type type;
@@ -20,7 +31,6 @@ typedef struct {
     struct {
       uint32_t timestamp;
     } buttonpress;
-    send_t send;
   };
 } event_t;
 
@@ -53,30 +63,72 @@ static void button_pressed() {
   }
 }
 
+static void time_to_send(uint _) {
+  /* This runs in interrupt context; don't linger.  */
+  event_t e;
+  e.type = SEND;
+  queue_try_add_ignoring_errors(&queue, &e);
+}
+
+void service_sleeps(int alarm, send_t *sleeping_sends, pheap_t *sleeps_heap) {
+  hardware_alarm_cancel(alarm);
+
+  while (1) {
+    uint32_t now = time_s();
+    pheap_node_id_t i = ph_peek_head(sleeps_heap);
+    if (i == 0)
+      return;
+    send_t *send = &sleeping_sends[i];
+    if (next_send(send) > now) {
+      uint32_t sleep_duration = next_send(send) - now;
+      if (hardware_alarm_set_target(
+              alarm, make_timeout_time_ms(sleep_duration * 1000)))
+        signal_error_by_blinking();
+      return;
+    }
+    if (ph_remove_head(sleeps_heap, false) != i)
+      signal_error_by_blinking();
+    uint32_t ago = now - send->timestamp;
+    send_report(send->seq, ago);
+    send->send_count++;
+    if (send->send_count < config_resend_count)
+      ph_insert_node(sleeps_heap, i);
+    else
+      ph_free_node(sleeps_heap, i);
+  }
+}
+
 void service_queue() {
+  int alarm = hardware_alarm_claim_unused(true);
+  if (alarm == -1)
+    signal_error_by_blinking();
+  hardware_alarm_set_callback(alarm, time_to_send);
+
+  send_t sleeping_sends[PICO_PHEAP_MAX_ENTRIES];
+  pheap_t *sleeps_heap =
+      ph_create(PICO_PHEAP_MAX_ENTRIES, next_send_less_than, sleeping_sends);
   u16_t seq = 0;
   while (1) {
+    service_sleeps(alarm, sleeping_sends, sleeps_heap);
+
     event_t e;
     queue_remove_blocking(&queue, &e);
     switch (e.type) {
     case BUTTONPRESS: {
-      event_t send_e;
-      send_e.type = SEND;
-      send_e.send.timestamp = e.buttonpress.timestamp;
-      send_e.send.seq = seq++;
-      send_e.send.send_count = 0;
-      queue_try_add_ignoring_errors(&queue, &send_e);
+      pheap_node_id_t i = ph_new_node(sleeps_heap);
+      if (i == 0) {
+        /* TODO: Don't drop new presses just because sleeps_heap is full of old
+         * presses. */
+        break;
+      }
+      sleeping_sends[i].timestamp = e.buttonpress.timestamp;
+      sleeping_sends[i].seq = seq++;
+      sleeping_sends[i].send_count = 0;
+      ph_insert_node(sleeps_heap, i);
     } break;
     case SEND: {
-      uint32_t now = time_s();
-      uint32_t ago = now - e.send.timestamp;
-      send_report(e.send.seq, ago);
-      e.send.send_count++;
-      if (e.send.send_count < config_resend_count)
-        queue_try_add_ignoring_errors(&queue, &e);
-      /* TODO: Sleep elsewhere. */
-      signal(e.send.send_count == 1 ? 2 : 1, 100);
-      sleep_ms(config_resend_interval_ms);
+      /* OK, we're awake. Cool. Thanks! (We actually do the sends in the
+       * service_sleeps() call at the top of the loop.)  */
     } break;
     default:
       signal_error_by_blinking();