Add SerialUSB::ignoreFlowControl() method (#1624)

Fixes #1620

cores/rp2040/SerialUSB.cpp

@@ -130,7 +130,7 @@ size_t SerialUSB::write(const uint8_t *buf, size_t length) {
 
     static uint64_t last_avail_time;
     int written = 0;
-    if (tud_cdc_connected()) {
+    if (tud_cdc_connected() || _ignoreFlowControl) {
         for (size_t i = 0; i < length;) {
             int n = length - i;
             int avail = tud_cdc_write_available();
@@ -171,6 +171,9 @@ SerialUSB::operator bool() {
     return tud_cdc_connected();
 }
 
+void SerialUSB::ignoreFlowControl(bool ignore) {
+    _ignoreFlowControl = ignore;
+}
 
 static bool _dtr = false;
 static bool _rts = false;

cores/rp2040/SerialUSB.h

@@ -44,6 +44,8 @@ public:
     using Print::write;
     operator bool() override;
 
+    void ignoreFlowControl(bool ignore = true);
+
     // ESP8266 compat
     void setDebugOutput(bool unused) {
         (void) unused;
@@ -51,6 +53,7 @@ public:
 
 private:
     bool _running = false;
+    bool _ignoreFlowControl = false;
 };
 
 extern SerialUSB Serial;