esp32/machine_uart: Change default UART(1) pins on ESP32 with SPIRAM.

dpgeorge · dpgeorge · commit 85a15f995c66 · 2026-01-13T13:43:02.000+11:00
SPIRAM usually uses GPIO 9 and 10 on ESP32, so don't use them as default UART pins. Fixes issue #18544. Signed-off-by: Damien George <damien@micropython.org>
diff --git a/docs/esp32/quickref.rst b/docs/esp32/quickref.rst
@@ -380,6 +380,9 @@ tx     1      10     17
 rx     3      9      16
 =====  =====  =====  =====
 
+On ESP32 with SPIRAM, the default pins for UART1 are ``tx=5`` and ``rx=4``
+to avoid possible conflicts with the SPIRAM pins.
+
 PWM (pulse width modulation)
 ----------------------------
 
diff --git a/ports/esp32/machine_uart.c b/ports/esp32/machine_uart.c
@@ -278,8 +278,14 @@ static void mp_machine_uart_init_helper(machine_uart_obj_t *self, size_t n_args,
                 self->tx = UART_PIN_NO_CHANGE; // GPIO 1
                 break;
             case UART_NUM_1:
+                #if CONFIG_IDF_TARGET_ESP32 && CONFIG_SPIRAM
+                // ESP32 usually uses pins 9 and 10 for SPIRAM bus, so avoid those pins as defaults.
+                self->rx = 4;
+                self->tx = 5;
+                #else
                 self->rx = 9;
                 self->tx = 10;
+                #endif
                 break;
             #if SOC_UART_HP_NUM > 2
             case UART_NUM_2:
