Add ::overflow() return to SerialUART/SerialPIO (#547)

Matching the Arduino SoftwareSerial API

cores/rp2040/SerialPIO.cpp

@@ -127,7 +127,7 @@ void __not_in_flash_func(SerialPIO::_handleIRQ)() {
             asm volatile("" ::: "memory"); // Ensure the queue is written before the written count advances
             _writer = next_writer;
         } else {
-            // TODO: Overflow
+            _overflow = true;
         }
     }
 }
@@ -146,6 +146,7 @@ SerialPIO::~SerialPIO() {
 }
 
 void SerialPIO::begin(unsigned long baud, uint16_t config) {
+    _overflow = false;
     _baud = baud;
     switch (config & SERIAL_PARITY_MASK) {
     case SERIAL_PARITY_EVEN:
@@ -289,6 +290,17 @@ int SerialPIO::read() {
     return -1;
 }
 
+bool SerialPIO::overflow() {
+    CoreMutex m(&_mutex);
+    if (!_running || !m || (_rx == NOPIN)) {
+        return false;
+    }
+
+    bool hold = _overflow;
+    _overflow = false;
+    return hold;
+}
+
 int SerialPIO::available() {
     CoreMutex m(&_mutex);
     if (!_running || !m || (_rx == NOPIN)) {

cores/rp2040/SerialPIO.h

@@ -47,6 +47,7 @@ public:
     virtual int availableForWrite() override;
     virtual void flush() override;
     virtual size_t write(uint8_t c) override;
+    bool overflow();
     using Print::write;
     operator bool() override;
 
@@ -60,6 +61,7 @@ private:
     int _bits;
     uart_parity_t _parity;
     int _stop;
+    bool _overflow;
     mutex_t _mutex;
 
     PIOProgram *_txPgm;

cores/rp2040/SerialUART.cpp

@@ -131,6 +131,7 @@ void SerialUART::begin(unsigned long baud, uint16_t config) {
     if (_running) {
         end();
     }
+    _overflow = false;
     _queue = new uint8_t[_fifoSize];
     _baud = baud;
     uart_init(_uart, baud);
@@ -271,6 +272,16 @@ int SerialUART::read() {
     return -1;
 }
 
+bool SerialUART::overflow() {
+    CoreMutex m(&_mutex);
+    if (!_running || !m) {
+        return false;
+    }
+    bool hold = _overflow;
+    _overflow = false;
+    return hold;
+}
+
 int SerialUART::available() {
     CoreMutex m(&_mutex);
     if (!_running || !m) {
@@ -387,7 +398,7 @@ void __not_in_flash_func(SerialUART::_handleIRQ)(bool inIRQ) {
             // Avoid using division or mod because the HW divider could be in use
             _writer = next_writer;
         } else {
-            // TODO: Overflow
+            _overflow = true;
         }
     }
     if (inIRQ) {

cores/rp2040/SerialUART.h

@@ -60,6 +60,7 @@ public:
     virtual size_t write(uint8_t c) override;
     virtual size_t write(const uint8_t *p, size_t len) override;
     using Print::write;
+    bool overflow();
     operator bool() override;
 
     // Not to be called by users, only from the IRQ handler.  In public so that the C-language IQR callback can access it
@@ -73,6 +74,7 @@ private:
     int _baud;
     mutex_t _mutex;
     bool _polling = false;
+    bool _overflow;
 
     // Lockless, IRQ-handled circular queue
     uint32_t _writer;