improve TinyUSB port

add yield to stream timeRead() timePeek() and Serial::bool()

cores/arduino/Adafruit_TinyUSB_Core/Adafruit_USBD_CDC.cpp

@@ -64,7 +64,13 @@ void Adafruit_USBD_CDC::end(void)
 
 Adafruit_USBD_CDC::operator bool()
 {
-  return tud_cdc_connected();
+  bool ret = tud_cdc_connected();
+
+  // Add an yield to run usb background in case sketch block wait as follows
+  // while(!Serial) {}
+  if ( !ret ) yield();
+
+  return ret;
 }
 
 int Adafruit_USBD_CDC::available(void)
@@ -82,11 +88,6 @@ int Adafruit_USBD_CDC::read(void)
   return (int) tud_cdc_read_char();
 }
 
-size_t Adafruit_USBD_CDC::readBytes(char *buffer, size_t length)
-{
-  return tud_cdc_read(buffer, length);
-}
-
 void Adafruit_USBD_CDC::flush(void)
 {
   tud_cdc_write_flush();

cores/arduino/Adafruit_TinyUSB_Core/Adafruit_USBD_CDC.h

@@ -51,9 +51,6 @@ public:
 	  return write((const uint8_t *)buffer, size);
 	}
 	operator bool();
-
-	size_t readBytes(char *buffer, size_t length);
-	size_t readBytes(uint8_t *buffer, size_t length) { return readBytes((char *)buffer, length); }
 };
 
 extern Adafruit_USBD_CDC Serial;

cores/arduino/Stream.cpp

@@ -35,6 +35,7 @@ int Stream::timedRead()
   do {
     c = read();
     if (c >= 0) return c;
+    yield(); // running TinyUSB task
   } while(millis() - _startMillis < _timeout);
   return -1;     // -1 indicates timeout
 }
@@ -47,6 +48,7 @@ int Stream::timedPeek()
   do {
     c = peek();
     if (c >= 0) return c;
+    yield(); // running TinyUSB task
   } while(millis() - _startMillis < _timeout);
   return -1;     // -1 indicates timeout
 }

cores/arduino/hooks.c

@@ -28,7 +28,17 @@
 static void __empty() {
 	// Empty
 }
+
+#ifdef USE_TINYUSB
+#include "tusb.h"
+void yield(void)
+{
+  tud_task();
+  tud_cdc_write_flush();
+}
+#else
 void yield(void) __attribute__ ((weak, alias("__empty")));
+#endif
 
 /**
  * SysTick hook

cores/arduino/main.cpp

@@ -52,23 +52,10 @@ int main( void )
   for (;;)
   {
     loop();
-
-#ifdef USE_TINYUSB
-    tud_task();
-    tud_cdc_write_flush();
-#endif
+    yield(); // yield run usb background task
 
     if (serialEventRun) serialEventRun();
   }
 
   return 0;
 }
-
-#ifdef USE_TINYUSB
-void yield(void)
-{
-  tud_task();
-  tud_cdc_write_flush();
-}
-#endif
-