Add setFIFOSize to UART Serial ports (#410)

Allow setting the size of the receive buffer by the application using a
call to Serial1/2.setFIFOSize(xxx) before the begin() call.

cores/rp2040/SerialPIO.cpp

@@ -127,7 +127,7 @@ void __not_in_flash_func(SerialPIO::_handleIRQ)() {
 SerialPIO::SerialPIO(pin_size_t tx, pin_size_t rx, size_t fifosize) {
     _tx = tx;
     _rx = rx;
-    _fifosize = fifosize;
+    _fifosize = fifosize + 1; // Always one unused entry
     _queue = new uint8_t[_fifosize];
     mutex_init(&_mutex);
 }

cores/rp2040/SerialUART.cpp

@@ -65,6 +65,14 @@ bool SerialUART::setTX(pin_size_t pin) {
     return false;
 }
 
+bool SerialUART::setFIFOSize(size_t size) {
+    if (!size || _running) {
+        return false;
+    }
+    _fifoSize = size + 1; // Always 1 unused entry
+    return true;
+}
+
 SerialUART::SerialUART(uart_inst_t *uart, pin_size_t tx, pin_size_t rx) {
     _uart = uart;
     _tx = tx;
@@ -76,6 +84,7 @@ static void _uart0IRQ();
 static void _uart1IRQ();
 
 void SerialUART::begin(unsigned long baud, uint16_t config) {
+    _queue = new uint8_t[_fifoSize];
     _baud = baud;
     uart_init(_uart, baud);
     int bits, stop;
@@ -140,6 +149,7 @@ void SerialUART::end() {
         irq_set_enabled(UART1_IRQ, false);
     }
     uart_deinit(_uart);
+    delete[] _queue;
     _running = false;
 }
 
@@ -170,7 +180,7 @@ int SerialUART::read() {
     while ((now - start) < _timeout) {
         if (_writer != _reader) {
             auto ret = _queue[_reader];
-            _reader = (_reader + 1) % sizeof(_queue);
+            _reader = (_reader + 1) % _fifoSize;
             return ret;
         }
         delay(1);
@@ -184,7 +194,7 @@ int SerialUART::available() {
     if (!_running || !m) {
         return 0;
     }
-    return (_writer - _reader) % sizeof(_queue);
+    return (_writer - _reader) % _fifoSize;
 }
 
 int SerialUART::availableForWrite() {
@@ -250,10 +260,10 @@ void __not_in_flash_func(SerialUART::_handleIRQ)() {
     uart_get_hw(_uart)->icr |= UART_UARTICR_RTIC_BITS | UART_UARTICR_RXIC_BITS;
     while (uart_is_readable(_uart)) {
         auto val = uart_getc(_uart);
-        if ((_writer + 1) % sizeof(_queue) != _reader) {
+        if ((_writer + 1) % _fifoSize != _reader) {
             _queue[_writer] = val;
             asm volatile("" ::: "memory"); // Ensure the queue is written before the written count advances
-            _writer = (_writer + 1) % sizeof(_queue);
+            _writer = (_writer + 1) % _fifoSize;
         } else {
             // TODO: Overflow
         }

cores/rp2040/SerialUART.h

@@ -40,6 +40,7 @@ public:
         ret &= setTX(tx);
         return ret;
     }
+    bool setFIFOSize(size_t size);
 
     void begin(unsigned long baud = 115200) override {
         begin(baud, SERIAL_8N1);
@@ -70,7 +71,8 @@ private:
     // Lockless, IRQ-handled circular queue
     uint32_t _writer;
     uint32_t _reader;
-    uint8_t  _queue[32];
+    size_t   _fifoSize = 32;
+    uint8_t  *_queue;
 };
 
 extern SerialUART Serial1; // HW UART 0

docs/serial.rst

@@ -24,5 +24,12 @@ Configure their pins using the ``setXXX`` calls prior to calling ``begin()``
         Serial1.setTX(pin);
         Serial1.begin(baud);
 
+The size of the receive FIFO may also be adjusted from the default 32 bytes by
+using the ``setFIFOSize`` call prior to calling ``begin()``
+
+.. code:: cpp
+        Serial1.setFIFOSize(128);
+        Serial1.begin(baud);
+
 For detailed information about the Serial ports, see the
 Arduino `Serial Reference <https://www.arduino.cc/reference/en/language/functions/communication/serial/>`_ .

keywords.txt

@@ -34,3 +34,4 @@ resumeOtherCore	KEYWORD2
 PIOProgram	KEYWORD2
 prepare	KEYWORD2
 SerialPIO	KEYWORD2
+setFIFOSize	KEYWORD2