Add DTR toggling sequence support

Enabled thanks: DTR_TOGGLING_SEQ
User can redefine its own hook by redefining:
dtr_togglingHook(uint8_t *buf, uint32_t *len)

Signed-off-by: BennehBoy <bennyboy@benneh.net>

Author: BennehBoy

cores/arduino/hooks.c

@@ -16,6 +16,8 @@
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
 
+#include <stdint.h>
+
 /**
  * Empty yield() hook.
  *
@@ -30,3 +32,21 @@ static void __empty()
   // Empty
 }
 void yield(void) __attribute__((weak, alias("__empty")));
+
+#ifdef DTR_TOGGLING_SEQ
+/**
+ * Empty dtr_toggling() hook.
+ *
+ * This function is intended to be used by library writers to build
+ * libraries or sketches that require DTR toggling feature.
+ *
+ * Its defined as a weak symbol and it can be redefined to implement
+ * task to achieve in this case.
+ */
+static void __empty_dtr_toggling(uint8_t *buf, uint32_t *len)
+{
+  (void)buf;
+  (void)len;
+}
+void dtr_togglingHook(uint8_t *buf, uint32_t *len) __attribute__((weak, alias("__empty_dtr_toggling")));
+#endif

cores/arduino/stm32/usb/cdc/usbd_cdc_if.c

@@ -54,6 +54,11 @@ __IO uint32_t lineState = 0;
 __IO bool receivePended = true;
 static uint32_t transmitStart = 0;
 
+#ifdef DTR_TOGGLING_SEQ
+/* DTR toggling sequence management */
+extern void dtr_togglingHook(uint8_t *buf, uint32_t *len);
+uint8_t dtr_toggling = 0;
+#endif
 
 /** USBD_CDC Private Function Prototypes */
 
@@ -182,6 +187,9 @@ static int8_t USBD_CDC_Control(uint8_t cmd, uint8_t *pbuf, uint16_t length)
       if (lineState) { // Reset the transmit timeout when the port is connected
         transmitStart = 0;
       }
+#ifdef DTR_TOGGLING_SEQ
+      dtr_toggling++; /* Count DTR toggling */
+#endif
       break;
 
     case CDC_SEND_BREAK:
@@ -213,7 +221,14 @@ static int8_t USBD_CDC_Control(uint8_t cmd, uint8_t *pbuf, uint16_t length)
   */
 static int8_t USBD_CDC_Receive(uint8_t *Buf, uint32_t *Len)
 {
+#ifdef DTR_TOGGLING_SEQ
+  if (dtr_toggling > 3) {
+    dtr_togglingHook(Buf, Len);
+    dtr_toggling = 0;
+  }
+#else
   UNUSED(Buf);
+#endif
   /* It always contains required amount of free space for writing */
   CDC_ReceiveQueue_CommitBlock(&ReceiveQueue, (uint16_t)(*Len));
   receivePended = false;