esp32: Fix first line ESP32-C2 serial output after reset or deepsleep.

ESP32-C2 ROM prints at 74880bps (same as ESP8266), so need a newline
before first MicroPython output to avoid it being appended on end of
a line of noise.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

ports/esp32/boards/ESP32_GENERIC_C2/board_init.c

@@ -0,0 +1,35 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2025 Angus Gratton
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#include "py/mpconfig.h"
+
+void GENERIC_C2_board_startup(void) {
+    // With a 26MHz crystal the ESP32-C2 ROM prints output at 74880 which is
+    // interpreted mostly as noise, then boot.py output and/or the REPL banner
+    // prints at the end of a line of noise unless we inject a newline here
+    printf("\n");
+
+    boardctrl_startup();
+}

ports/esp32/boards/ESP32_GENERIC_C2/mpconfigboard.cmake

@@ -7,3 +7,8 @@ set(SDKCONFIG_DEFAULTS
     # C2 has unusably low free RAM without these optimisations
     boards/sdkconfig.free_ram
 )
+
+set(MICROPY_SOURCE_BOARD
+    ${MICROPY_BOARD_DIR}/board_init.c
+)
+

ports/esp32/boards/ESP32_GENERIC_C2/mpconfigboard.h

@@ -5,3 +5,6 @@
 
 #define MICROPY_HW_ENABLE_SDCARD            (0)
 #define MICROPY_PY_MACHINE_I2S              (0)
+
+#define MICROPY_BOARD_STARTUP               GENERIC_C2_board_startup
+void GENERIC_C2_board_startup(void);

ports/esp32/boards/sdkconfig.c2

@@ -4,6 +4,12 @@
 CONFIG_XTAL_FREQ_26=y
 # CONFIG_XTAL_FREQ_40 is not set
 CONFIG_XTAL_FREQ=26
+
+# When using 26MHz crystal the baud rate defaults to 74880,
+# same as ESP8266 - MicroPython uses 115200, so switch early
+CONFIG_ESP_CONSOLE_UART_CUSTOM=y
+CONFIG_ESP_CONSOLE_UART_BAUDRATE=115200
+
 # Increase NimBLE stack size for functional BT
 CONFIG_BT_NIMBLE_TASK_STACK_SIZE=5120