Add rate limiting for cloud serial

It looks like lastCloudEvent was intended to be used for rate limiting,
since it's not used anywhere else, but it was being updated every time
spark_process() ran, not just when data was actually sent. Changed it
to update only when data is sent.

cores/oak/OakParticle/particle_core.cpp

@@ -3048,7 +3048,10 @@ void spark_process(bool internal, bool allow_connect)
       return;
     }
     if(spark_connected()){
-        spark_send_tx();
+        if(millis() - lastCloudEvent > 1000){
+            if(spark_send_tx()>0)
+                lastCloudEvent = millis();
+        }
         if(!event_loop()){
             if(pClient.connected()){
               pClient.stop();
@@ -3070,7 +3073,6 @@ void spark_process(bool internal, bool allow_connect)
       else
         return;
     }
-    lastCloudEvent = millis();
 }
 
 #define MAX_SERIAL_BUFF 255
@@ -3202,13 +3204,14 @@ void spark_get_rx(const char* name, const char* data){ //this is automatically c
     }
 }
 
-void spark_send_tx(){
+int spark_send_tx(){
     if(spark_transmit_buffer_count == 0)//nothing buffer
+        return 0;
 
-        return;
     char buff[spark_transmit_buffer_count+1];
+    uint8_t b;
 
-    for(uint8_t b=0;b<spark_transmit_buffer_count;b++){
+    for(b=0;b<spark_transmit_buffer_count;b++){
         // Read from "head"
         buff[b] = spark_transmit_buffer[spark_transmit_buffer_head]; // grab next byte
         spark_transmit_buffer_head = (spark_transmit_buffer_head + 1) % MAX_SERIAL_BUFF;
@@ -3222,6 +3225,8 @@ void spark_send_tx(){
     spark_transmit_buffer_count=0;
 
     spark_send_event("oak/device/stdout", buff, 60, PRIVATE, NULL);
+
+    return b;
 }
 
 

cores/oak/OakParticle/particle_core.h

@@ -248,7 +248,7 @@ size_t spark_serial_write(uint8_t b);
 void spark_serial_flush();
 int spark_serial_peek();
 void spark_get_rx(const char* name, const char* data);
-void spark_send_tx();
+int spark_send_tx();
 void spark_process(bool internal = false,bool allow_connect = true);
 
 String info_response(void);