Implement tx open drain. (#239)

Author: dok-net

library.json

@@ -1,6 +1,6 @@
 {
     "name": "EspSoftwareSerial",
-    "version": "6.16.1",
+    "version": "6.17.0",
     "description": "Implementation of the Arduino software serial for ESP8266/ESP32.",
     "keywords": [
         "serial", "io", "softwareserial"

library.properties

@@ -1,5 +1,5 @@
 name=EspSoftwareSerial
-version=6.16.1
+version=6.17.0
 author=Dirk Kaar, Peter Lerup
 maintainer=Dirk Kaar <dok@dok-net.net>
 sentence=Implementation of the Arduino software serial for ESP8266/ESP32.

src/SoftwareSerial.cpp

@@ -51,13 +51,15 @@ constexpr uint8_t BYTE_ALL_BITS_SET = ~static_cast<uint8_t>(0);
 
 SoftwareSerial::SoftwareSerial() {
     m_isrOverflow = false;
-    m_rxGPIOPullupEnabled = true;
+    m_rxGPIOPullUpEnabled = true;
+    m_txGPIOOpenDrain = false;
 }
 
 SoftwareSerial::SoftwareSerial(int8_t rxPin, int8_t txPin, bool invert)
 {
     m_isrOverflow = false;
-    m_rxGPIOPullupEnabled = true;
+    m_rxGPIOPullUpEnabled = true;
+    m_txGPIOOpenDrain = false;
     m_rxPin = rxPin;
     m_txPin = txPin;
     m_invert = invert;
@@ -67,7 +69,10 @@ SoftwareSerial::~SoftwareSerial() {
     end();
 }
 
-bool SoftwareSerial::isValidGPIOpin(int8_t pin) {
+#if __GNUC__ >= 10
+constexpr
+#endif
+bool SoftwareSerial::isValidGPIOpin(int8_t pin) const {
 #if defined(ESP8266)
     return (pin >= 0 && pin <= 16) && !isFlashInterfacePin(pin);
 #elif defined(ESP32)
@@ -97,15 +102,21 @@ bool SoftwareSerial::isValidGPIOpin(int8_t pin) {
 #endif
 }
 
-bool SoftwareSerial::isValidRxGPIOpin(int8_t pin) {
+#if __GNUC__ >= 10
+constexpr
+#endif
+bool SoftwareSerial::isValidRxGPIOpin(int8_t pin) const {
     return isValidGPIOpin(pin)
 #if defined(ESP8266)
         && (pin != 16)
 #endif
         ;
 }
 
-bool SoftwareSerial::isValidTxGPIOpin(int8_t pin) {
+#if __GNUC__ >= 10
+constexpr
+#endif
+bool SoftwareSerial::isValidTxGPIOpin(int8_t pin) const {
     return isValidGPIOpin(pin)
 #if defined(ESP32)
 #ifdef CONFIG_IDF_TARGET_ESP32
@@ -119,7 +130,10 @@ bool SoftwareSerial::isValidTxGPIOpin(int8_t pin) {
         ;
 }
 
-bool SoftwareSerial::hasRxGPIOPullUp(int8_t pin) {
+#if __GNUC__ >= 10
+constexpr
+#endif
+bool SoftwareSerial::hasRxGPIOPullUp(int8_t pin) const {
 #if defined(ESP32)
     return !(pin >= 34 && pin <= 39);
 #else
@@ -128,9 +142,15 @@ bool SoftwareSerial::hasRxGPIOPullUp(int8_t pin) {
 #endif
 }
 
-void SoftwareSerial::setRxGPIOPullUp() {
+void SoftwareSerial::setRxGPIOPinMode() {
     if (m_rxValid) {
-        pinMode(m_rxPin, hasRxGPIOPullUp(m_rxPin) && m_rxGPIOPullupEnabled ? INPUT_PULLUP : INPUT);
+        pinMode(m_rxPin, hasRxGPIOPullUp(m_rxPin) && m_rxGPIOPullUpEnabled ? INPUT_PULLUP : INPUT);
+    }
+}
+
+void SoftwareSerial::setTxGPIOPinMode() {
+    if (m_txValid) {
+        pinMode(m_txPin, m_txGPIOOpenDrain ? OUTPUT_OPEN_DRAIN : OUTPUT);
     }
 }
 
@@ -160,7 +180,7 @@ void SoftwareSerial::begin(uint32_t baud, SoftwareSerialConfig config,
             isrBufCapacity : m_buffer->capacity() * (2 + m_dataBits + static_cast<bool>(m_parityMode))));
         if (m_buffer && (!m_parityMode || m_parityBuffer) && m_isrBuffer) {
             m_rxValid = true;
-            setRxGPIOPullUp();
+            setRxGPIOPinMode();
         }
     }
     if (isValidTxGPIOpin(m_txPin)) {
@@ -170,7 +190,7 @@ void SoftwareSerial::begin(uint32_t baud, SoftwareSerialConfig config,
         m_txBitMask = digitalPinToBitMask(m_txPin);
         m_txValid = true;
         if (!m_oneWire) {
-            pinMode(m_txPin, OUTPUT);
+            setTxGPIOPinMode();
             digitalWrite(m_txPin, !m_invert);
         }
     }
@@ -210,20 +230,25 @@ void SoftwareSerial::enableIntTx(bool on) {
     m_intTxEnabled = on;
 }
 
-void SoftwareSerial::enableRxGPIOPullup(bool on) {
-    m_rxGPIOPullupEnabled = on;
-    setRxGPIOPullUp();
+void SoftwareSerial::enableRxGPIOPullUp(bool on) {
+    m_rxGPIOPullUpEnabled = on;
+    setRxGPIOPinMode();
+}
+
+void SoftwareSerial::enableTxGPIOOpenDrain(bool on) {
+    m_txGPIOOpenDrain = on;
+    setTxGPIOPinMode();
 }
 
 void SoftwareSerial::enableTx(bool on) {
     if (m_txValid && m_oneWire) {
         if (on) {
             enableRx(false);
-            pinMode(m_txPin, OUTPUT);
+            setTxGPIOPinMode();
             digitalWrite(m_txPin, !m_invert);
         }
         else {
-            setRxGPIOPullUp();
+            setRxGPIOPinMode();
             enableRx(true);
         }
     }

src/SoftwareSerial.h

@@ -124,8 +124,10 @@ class SoftwareSerial : public Stream {
     void setTransmitEnablePin(int8_t txEnablePin);
     /// Enable (default) or disable interrupts during tx.
     void enableIntTx(bool on);
-    /// Enable (default) or disable internal rx GPIO pullup.
-    void enableRxGPIOPullup(bool on);
+    /// Enable (default) or disable internal rx GPIO pull-up.
+    void enableRxGPIOPullUp(bool on);
+    /// Enable or disable (default) tx GPIO output mode.
+    void enableTxGPIOOpenDrain(bool on);
 
     bool overflow();
 
@@ -221,13 +223,15 @@ class SoftwareSerial : public Stream {
     // If offCycle == 0, the level remains unchanged from dutyCycle.
     void writePeriod(
         uint32_t dutyCycle, uint32_t offCycle, bool withStopBit);
-    bool isValidGPIOpin(int8_t pin);
-    bool isValidRxGPIOpin(int8_t pin);
-    bool isValidTxGPIOpin(int8_t pin);
+    constexpr bool isValidGPIOpin(int8_t pin) const;
+    constexpr bool isValidRxGPIOpin(int8_t pin) const;
+    constexpr bool isValidTxGPIOpin(int8_t pin) const;
     // result is only defined for a valid Rx GPIO pin
-    bool hasRxGPIOPullUp(int8_t pin);
+    constexpr bool hasRxGPIOPullUp(int8_t pin) const;
     // safely set the pin mode for the Rx GPIO pin
-    void setRxGPIOPullUp();
+    void setRxGPIOPinMode();
+    // safely set the pin mode for the Tx GPIO pin
+    void setTxGPIOPinMode();
     /* check m_rxValid that calling is safe */
     void rxBits();
     void rxBits(const uint32_t isrTick);
@@ -264,7 +268,8 @@ class SoftwareSerial : public Stream {
     /// PDU bits include data, parity and stop bits; the start bit is not counted.
     uint8_t m_pduBits;
     bool m_intTxEnabled;
-    bool m_rxGPIOPullupEnabled;
+    bool m_rxGPIOPullUpEnabled;
+    bool m_txGPIOOpenDrain;
     SoftwareSerialParity m_parityMode;
     uint8_t m_stopBits;
     bool m_lastReadParity;