Add an option to force IDF's default UART clock source

Author: gonzabrusco

Kconfig.projbuild

@@ -118,6 +118,17 @@ config ARDUINO_SERIAL_EVENT_TASK_PRIORITY
     help
         Select at what priority you want the Serial Event task to run.
 
+config ARDUINO_SERIAL_FORCE_IDF_DEFAULT_CLOCK_SOURCE
+    bool "Force IDF default UART clock source"
+    default "n"
+    help
+        Overrides Arduino's automatic UART clock selection with the default clock from IDF (clk_tree_defs.h).
+        By default, Arduino optimizes the UART clock automatically: XTAL clock for C2, S3, C3, C6, H2, P4 and 
+        REF_TICK (<250k baud) or APB (>250k baud) for ESP32, S2.
+        Enable this option only if you need to force IDF's default clock instead of Arduino's optimized settings.
+        It is generally recommended to leave this disabled unless specifically required.
+        Note: This configuration is not applicable to the low-power (LP) UART controller.
+
 choice ARDUINO_UDP_RUNNING_CORE
     bool "Core on which Arduino's UDP is running"
     default ARDUINO_UDP_RUN_CORE0

cores/esp32/esp32-hal-uart.c

@@ -670,6 +670,11 @@ uart_t *uartBegin(
   } else
 #endif
   {
+#if CONFIG_ARDUINO_SERIAL_FORCE_IDF_DEFAULT_CLOCK_SOURCE
+    // Default CLK Source: CLK_APB for ESP32|S2|S3|C3 -- CLK_PLL_F40M for C2 -- CLK_PLL_F48M for H2 -- CLK_PLL_F80M for C6|P4
+    uart_config.source_clk = UART_SCLK_DEFAULT;  // baudrate may change with the APB Frequency!
+    log_v("Setting UART%d to use DEFAULT clock", uart_nr);
+#else
     // there is an issue when returning from light sleep with the C6 and H2: the uart baud rate is not restored
     // therefore, uart clock source will set to XTAL for all SoC that support it. This fix solves the C6|H2 issue.
 #if SOC_UART_SUPPORT_XTAL_CLK
@@ -684,9 +689,10 @@ uart_t *uartBegin(
       log_v("Setting UART%d to use APB clock", uart_nr);
     }
 #else
-    // Default CLK Source: CLK_APB for ESP32|S2|S3|C3 -- CLK_PLL_F40M for C2 -- CLK_PLL_F48M for H2 -- CLK_PLL_F80M for C6
+    // Default CLK Source: CLK_APB for ESP32|S2|S3|C3 -- CLK_PLL_F40M for C2 -- CLK_PLL_F48M for H2 -- CLK_PLL_F80M for C6|P4
     uart_config.source_clk = UART_SCLK_DEFAULT;  // baudrate may change with the APB Frequency!
     log_v("Setting UART%d to use DEFAULT clock", uart_nr);
+#endif
 #endif
   }