optimistic_yield()

this introduces optimistic_yield() used for when standard library
methods are normally used in tight loops waiting for something to
happen, like available().

README.md

@@ -218,6 +218,7 @@ Libraries that don't rely on low-level access to AVR registers should work well.
 - [PubSubClient](https://github.com/Imroy/pubsubclient) MQTT library by @Imroy.
 - [RTC](https://github.com/Makuna/Rtc) - Arduino Library for Ds1307 & Ds3231 compatible with esp8266.
 - [Souliss, Smart Home](https://github.com/souliss/souliss) - Framework for Smart Home based on Arduino, Android and openHAB.
+- [ST7735](https://github.com/nzmichaelh/Adafruit-ST7735-Library) - Adafruit's ST7735 library modified to be compatible with esp8266.  Just make sure to modify the pins in the examples as they are still AVR specific.
 
 #### Upload via serial port ####
 Pick the correct serial port.

cores/esp8266/HardwareSerial.cpp

@@ -551,14 +551,20 @@ bool HardwareSerial::isRxEnabled(void) {
     return _uart->rxEnabled;
 }
 
+extern "C" void optimistic_yield();
+
 int HardwareSerial::available(void) {
-    if(_uart == 0)
-        return 0;
-    if(_uart->rxEnabled) {
-        return static_cast<int>(_rx_buffer->getSize());
-    } else {
-        return 0;
+    int result = 0;
+
+    if (_uart != NULL && _uart->rxEnabled) {
+        result = static_cast<int>(_rx_buffer->getSize());
     }
+
+    if (!result) {
+        optimistic_yield();
+    }
+
+    return result;
 }
 
 int HardwareSerial::peek(void) {

cores/esp8266/core_esp8266_main.cpp

@@ -34,6 +34,8 @@ extern "C" {
 #define LOOP_TASK_PRIORITY 0
 #define LOOP_QUEUE_SIZE    1
 
+#define OPTIMISTIC_YIELD_TIME_US 16000
+
 struct rst_info resetInfo;
 
 int atexit(void (*func)()) {
@@ -62,11 +64,8 @@ extern void (*__init_array_end)(void);
 cont_t g_cont __attribute__ ((aligned (16)));
 static os_event_t g_loop_queue[LOOP_QUEUE_SIZE];
 
-static uint32_t g_micros_at_task_start;
+static uint32_t g_micros_at_last_task_yield;
 
-extern "C" uint32_t esp_micros_at_task_start() {
-    return g_micros_at_task_start;
-}
 
 extern "C" void abort() {
     while(1) {
@@ -74,6 +73,7 @@ extern "C" void abort() {
 }
 
 extern "C" void esp_yield() {
+    g_micros_at_last_task_yield = system_get_time();
     cont_yield(&g_cont);
 }
 
@@ -87,6 +87,13 @@ extern "C" void __yield() {
 }
 extern "C" void yield(void) __attribute__ ((weak, alias("__yield")));
 
+extern "C" void optimistic_yield() {
+    if (system_get_time() - g_micros_at_last_task_yield > OPTIMISTIC_YIELD_TIME_US)
+    {
+        __yield();
+    }
+}
+
 static void loop_wrapper() {
     static bool setup_done = false;
     if(!setup_done) {
@@ -99,7 +106,7 @@ static void loop_wrapper() {
 }
 
 static void loop_task(os_event_t *events) {
-    g_micros_at_task_start = system_get_time();
+    g_micros_at_last_task_yield = system_get_time();
     cont_run(&g_cont, &loop_wrapper);
     if(cont_check(&g_cont) != 0) {
         ets_printf("\r\nheap collided with sketch stack\r\n");

libraries/ESP8266WiFi/src/WiFiClient.cpp

@@ -177,20 +177,19 @@ size_t WiFiClient::write(const uint8_t *buf, size_t size)
     return _client->write(reinterpret_cast<const char*>(buf), size);
 }
 
-extern "C" uint32_t esp_micros_at_task_start();
+extern "C" void optimistic_yield();
 
 int WiFiClient::available()
 {
-    static uint32_t lastPollTime = 0;
-    if (!_client)
-        return 0;
+    int result = 0;
 
-    if (lastPollTime > esp_micros_at_task_start())
-        yield();
+    if (_client) {
+        result = _client->getSize();
+    }
 
-    lastPollTime = micros();
-
-    int result = _client->getSize();
+    if (!result) {
+        optimistic_yield();
+    }
     return result;
 }
 

libraries/ESP8266WiFi/src/WiFiServer.cpp

@@ -84,17 +84,15 @@ bool WiFiServer::getNoDelay(){
   return tcp_nagle_disabled(_pcb);
 }
 
-extern "C" uint32_t esp_micros_at_task_start();
-
 bool WiFiServer::hasClient(){
   if (_unclaimed) return true;
   return false;
 }
 
+extern "C" void optimistic_yield();
+
 WiFiClient WiFiServer::available(byte* status)
 {
-    static uint32_t lastPollTime = 0;
-
     if (_unclaimed)
     {
         WiFiClient result(_unclaimed);
@@ -103,9 +101,7 @@ WiFiClient WiFiServer::available(byte* status)
         return result;
     }
 
-    if (lastPollTime > esp_micros_at_task_start())
-        yield();
-    lastPollTime = micros();
+    optimistic_yield();
 
     return WiFiClient();
 }

libraries/ESP8266WiFi/src/WiFiUdp.cpp

@@ -113,12 +113,22 @@ uint8_t WiFiUDP::beginMulticast(IPAddress interfaceAddr, IPAddress multicast, ui
     return 1;
 }
 
+extern "C" void optimistic_yield();
+
 /* return number of bytes available in the current packet,
    will return zero if parsePacket hasn't been called yet */
 int WiFiUDP::available() {
-    if (!_ctx)
-        return 0;
-    return static_cast<int>(_ctx->getSize());
+    int result = 0;
+
+    if (_ctx) {
+        result = static_cast<int>(_ctx->getSize());
+    }
+
+    if (!result) {
+        optimistic_yield();
+    }
+
+    return result;
 }
 
 /* Release any resources being used by this WiFiUDP instance */

libraries/Wire/Wire.cpp

@@ -160,8 +160,16 @@ size_t TwoWire::write(const uint8_t *data, size_t quantity){
   return quantity;
 }
 
+extern "C" void optimistic_yield();
+
 int TwoWire::available(void){
-  return rxBufferLength - rxBufferIndex;
+    int result = rxBufferLength - rxBufferIndex;
+
+    if (!result) {
+        optimistic_yield();
+    }
+
+    return result;
 }
 
 int TwoWire::read(void){