stm32/main: Make board-defined UART REPL use a static object and buffer.

This way the UART REPL does not need the MicroPython heap and exists
outside the MicroPython runtime, allowing characters to still be received
during a soft reset.

ports/stm32/main.c

@@ -73,6 +73,14 @@ STATIC pyb_thread_t pyb_thread_main;
 STATIC fs_user_mount_t fs_user_mount_flash;
 #endif
 
+#if defined(MICROPY_HW_UART_REPL)
+#ifndef MICROPY_HW_UART_REPL_RXBUF
+#define MICROPY_HW_UART_REPL_RXBUF (64)
+#endif
+STATIC pyb_uart_obj_t pyb_uart_repl_obj;
+STATIC uint8_t pyb_uart_repl_rxbuf[MICROPY_HW_UART_REPL_RXBUF];
+#endif
+
 void flash_error(int n) {
     for (int i = 0; i < n; i++) {
         led_state(PYB_LED_RED, 1);
@@ -541,6 +549,19 @@ void stm32_main(uint32_t reset_mode) {
     lwip_init();
     #endif
 
+    #if defined(MICROPY_HW_UART_REPL)
+    // Set up a UART REPL using a statically allocated object
+    pyb_uart_repl_obj.base.type = &pyb_uart_type;
+    pyb_uart_repl_obj.uart_id = MICROPY_HW_UART_REPL;
+    pyb_uart_repl_obj.is_static = true;
+    pyb_uart_repl_obj.timeout = 0;
+    pyb_uart_repl_obj.timeout_char = 2;
+    uart_init(&pyb_uart_repl_obj, MICROPY_HW_UART_REPL_BAUD, UART_WORDLENGTH_8B, UART_PARITY_NONE, UART_STOPBITS_1, 0);
+    uart_set_rxbuf(&pyb_uart_repl_obj, sizeof(pyb_uart_repl_rxbuf), pyb_uart_repl_rxbuf);
+    uart_attach_to_repl(&pyb_uart_repl_obj, true);
+    MP_STATE_PORT(pyb_uart_obj_all)[MICROPY_HW_UART_REPL - 1] = &pyb_uart_repl_obj;
+    #endif
+
 soft_reset:
 
     #if defined(MICROPY_HW_LED2)
@@ -588,27 +609,17 @@ soft_reset:
     // we can run Python scripts (eg boot.py), but anything that is configurable
     // by boot.py must be set after boot.py is run.
 
-    readline_init0();
-    pin_init0();
-    extint_init0();
-    timer_init0();
-
-    // Define MICROPY_HW_UART_REPL to be PYB_UART_6 and define
-    // MICROPY_HW_UART_REPL_BAUD in your mpconfigboard.h file if you want a
-    // REPL on a hardware UART as well as on USB VCP
     #if defined(MICROPY_HW_UART_REPL)
-    {
-        mp_obj_t args[2] = {
-            MP_OBJ_NEW_SMALL_INT(MICROPY_HW_UART_REPL),
-            MP_OBJ_NEW_SMALL_INT(MICROPY_HW_UART_REPL_BAUD),
-        };
-        MP_STATE_PORT(pyb_stdio_uart) = pyb_uart_type.make_new((mp_obj_t)&pyb_uart_type, MP_ARRAY_SIZE(args), 0, args);
-        uart_attach_to_repl(MP_STATE_PORT(pyb_stdio_uart), true);
-    }
+    MP_STATE_PORT(pyb_stdio_uart) = &pyb_uart_repl_obj;
     #else
     MP_STATE_PORT(pyb_stdio_uart) = NULL;
     #endif
 
+    readline_init0();
+    pin_init0();
+    extint_init0();
+    timer_init0();
+
     #if MICROPY_HW_ENABLE_CAN
     can_init0();
     #endif