[SERIAL] Make SERIAL gateway frame format (data/parity/stop bits) configurable (#2342)

Serial.begin() was hardcoded to SERIAL_8N1 across all four UART init paths
(UART0/1/2/3), with no way to override it via a build flag -- unlike SERIALBaud,
which already is. Devices using non-8N1 framing (e.g. even-parity RS232 sources)
currently can't be read correctly at all, not just unreliably: a parity mismatch
misaligns the frame, not just adds occasional noise.

Adds SERIAL_CONFIG following the existing #ifndef/#define override pattern used
throughout this codebase, defaulting to SERIAL_8N1 so existing environments are
unaffected byte-for-byte. Verified: default (SERIAL_8N1) and an override
(SERIAL_CONFIG=SERIAL_8E1) both build successfully on ESP32.

Co-authored-by: simowilso <simowilso@users.noreply.github.com>
Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

main/config_SERIAL.h

@@ -81,6 +81,10 @@ extern bool XtoSERIAL(const char* topicOri, JsonObject& SERIALdata);
 #  define SERIALBaud 9600 // The serial connection Baud
 #endif
 
+#ifndef SERIAL_CONFIG
+#  define SERIAL_CONFIG SERIAL_8N1 // The serial frame format (data/parity/stop bits), e.g. SERIAL_8E1 for 8 data bits/even parity/1 stop bit
+#endif
+
 /*-------------------PIN DEFINITIONS----------------------*/
 #ifndef SERIAL_UART
 // set hardware serial UART to be used for device communication or

main/gatewaySERIAL.cpp

@@ -78,9 +78,9 @@ void setupSERIAL() {
 #    if SERIAL_UART == 0 // init UART0
   Serial.end(); // stop if already initialized
 #      ifdef ESP32
-  Serial.begin(SERIALBaud, SERIAL_8N1, SERIAL_RX_GPIO, SERIAL_TX_GPIO);
+  Serial.begin(SERIALBaud, SERIAL_CONFIG, SERIAL_RX_GPIO, SERIAL_TX_GPIO);
 #      else
-  Serial.begin(SERIALBaud, SERIAL_8N1);
+  Serial.begin(SERIALBaud, SERIAL_CONFIG);
 #      endif
 #      if defined(ESP8266) && defined(SERIAL_UART0_SWAP)
   Serial.swap(); // swap UART0 ports from (GPIO1,GPIO3) to (GPIO15,GPIO13)
@@ -91,9 +91,9 @@ void setupSERIAL() {
 #    elif SERIAL_UART == 1 // init UART1
   Serial1.end(); // stop if already initialized
 #      ifdef ESP32
-  Serial1.begin(SERIALBaud, SERIAL_8N1, SERIAL_RX_GPIO, SERIAL_TX_GPIO);
+  Serial1.begin(SERIALBaud, SERIAL_CONFIG, SERIAL_RX_GPIO, SERIAL_TX_GPIO);
 #      else
-  Serial1.begin(SERIALBaud, SERIAL_8N1);
+  Serial1.begin(SERIALBaud, SERIAL_CONFIG);
 #      endif
   SERIALStream = &Serial1;
   THEENGS_LOG_NOTICE(F("SERIAL HW UART1" CR));
@@ -101,16 +101,16 @@ void setupSERIAL() {
 #    elif SERIAL_UART == 2 // init UART2
   Serial2.end(); // stop if already initialized
 #      ifdef ESP32
-  Serial2.begin(SERIALBaud, SERIAL_8N1, SERIAL_RX_GPIO, SERIAL_TX_GPIO);
+  Serial2.begin(SERIALBaud, SERIAL_CONFIG, SERIAL_RX_GPIO, SERIAL_TX_GPIO);
 #      else
-  Serial2.begin(SERIALBaud, SERIAL_8N1);
+  Serial2.begin(SERIALBaud, SERIAL_CONFIG);
 #      endif
   SERIALStream = &Serial2;
   THEENGS_LOG_NOTICE(F("SERIAL HW UART2" CR));
 
 #    elif SERIAL_UART == 3 // init UART3
   Serial3.end(); // stop if already initialized
-  Serial3.begin(SERIALBaud, SERIAL_8N1);
+  Serial3.begin(SERIALBaud, SERIAL_CONFIG);
   SERIALStream = &Serial3;
   THEENGS_LOG_NOTICE(F("SERIAL HW UART3" CR));
 #    endif