added setClockSource to enable a custom clock source for deep sleep applications

Author: jmpmscorp

README.md

@@ -146,7 +146,16 @@ void setOptions(int keepAlive, bool cleanSession, int timeout);
 
 - The `keepAlive` option controls the keep alive interval in seconds (default: 10).
 - The `cleanSession` option controls the session retention on the broker side (default: true).
-- The `timeout` option controls the default timeout for all commands in milliseconds (default: 1000). 
+- The `timeout` option controls the default timeout for all commands in milliseconds (default: 1000).
+
+Set a custom clock source "custom millis" callback to enable deep sleep applications:
+
+```c++
+void setClockSource(MQTTClientClockSource);
+// Callback signature: uint32_t clockSource() {}
+```
+
+- The specified callback is used by the internal timers to get a monotonic time in milliseconds. Since the clock source for the built-in `millis` is stopped when the the Arduino goes into deep sleep, you need to provide a custom callback that first syncs with a built-in or external Real Time Clock (RTC). You can pass `NULL` to reset to the default implementation.
 
 Connect to broker using the supplied client id and an optional username and password:
 

src/MQTTClient.cpp

@@ -5,15 +5,23 @@ inline void lwmqtt_arduino_timer_set(void *ref, uint32_t timeout) {
   auto t = (lwmqtt_arduino_timer_t *)ref;
 
   // set future end time
-  t->end = (uint32_t)(millis() + timeout);
+  if (t->millis != nullptr) {
+    t->end = (uint32_t)(t->millis() + timeout);
+  } else {
+    t->end = (uint32_t)(millis() + timeout);
+  }
 }
 
 inline int32_t lwmqtt_arduino_timer_get(void *ref) {
   // cast timer reference
   auto t = (lwmqtt_arduino_timer_t *)ref;
 
   // get difference to end time
-  return (int32_t)t->end - (int32_t)millis();
+  if (t->millis != nullptr) {
+    return (int32_t)(t->end - t->millis());
+  } else {
+    return (int32_t)(t->end - millis());
+  }
 }
 
 inline lwmqtt_err_t lwmqtt_arduino_network_read(void *ref, uint8_t *buffer, size_t len, size_t *read,
@@ -144,6 +152,11 @@ void MQTTClient::onMessageAdvanced(MQTTClientCallbackAdvanced cb) {
   this->callback.advanced = cb;
 }
 
+void MQTTClient::setClockSource(MQTTClientClockSource cb) {
+  this->timer1.millis = cb;
+  this->timer2.millis = cb;
+}
+
 void MQTTClient::setHost(const char hostname[], int port) {
   // free hostname if set
   if (this->hostname != nullptr) {

src/MQTTClient.h

@@ -9,8 +9,11 @@ extern "C" {
 #include "lwmqtt/lwmqtt.h"
 };
 
+typedef uint32_t (*MQTTClientClockSource)();
+
 typedef struct {
   uint32_t end;
+  MQTTClientClockSource millis;
 } lwmqtt_arduino_timer_t;
 
 typedef struct {
@@ -45,8 +48,8 @@ class MQTTClient {
   MQTTClientCallback callback;
 
   lwmqtt_arduino_network_t network = {nullptr};
-  lwmqtt_arduino_timer_t timer1 = {0};
-  lwmqtt_arduino_timer_t timer2 = {0};
+  lwmqtt_arduino_timer_t timer1 = {0, nullptr};
+  lwmqtt_arduino_timer_t timer2 = {0, nullptr};
   lwmqtt_client_t client = {0};
 
   bool _connected = false;
@@ -64,6 +67,8 @@ class MQTTClient {
   void onMessage(MQTTClientCallbackSimple cb);
   void onMessageAdvanced(MQTTClientCallbackAdvanced cb);
 
+  void setClockSource(MQTTClientClockSource cb);
+
   void setHost(const char hostname[]) { this->setHost(hostname, 1883); }
   void setHost(const char hostname[], int port);