esp32: Make machine.soft_reset() work in main.py and reset_cause().

This commit fixes two issues on the esp32:
- it enables machine.soft_reset() to be called in main.py;
- it enables machine.reset_cause() to correctly identify a soft reset.

The former is useful in that it enables soft resets in applications that
are started at boot time.  The support is patterned after the stm32 port.

ports/esp32/main.c

@@ -73,6 +73,7 @@ void mp_task(void *pvParameter) {
     mp_thread_init(pxTaskGetStackStart(NULL), MP_TASK_STACK_SIZE / sizeof(uintptr_t));
     #endif
     uart_init();
+    machine_init();
 
     // TODO: CONFIG_SPIRAM_SUPPORT is for 3.3 compatibility, remove after move to 4.0.
     #if CONFIG_ESP32_SPIRAM_SUPPORT || CONFIG_SPIRAM_SUPPORT
@@ -118,7 +119,10 @@ soft_reset:
     pyexec_frozen_module("_boot.py");
     pyexec_file_if_exists("boot.py");
     if (pyexec_mode_kind == PYEXEC_MODE_FRIENDLY_REPL) {
-        pyexec_file_if_exists("main.py");
+        int ret = pyexec_file_if_exists("main.py");
+        if (ret & PYEXEC_FORCED_EXIT) {
+            goto soft_reset_exit;
+        }
     }
 
     for (;;) {
@@ -135,6 +139,8 @@ soft_reset:
         }
     }
 
+soft_reset_exit:
+
     #if MICROPY_BLUETOOTH_NIMBLE
     mp_bluetooth_deinit();
     #endif
@@ -151,6 +157,7 @@ soft_reset:
 
     // deinitialise peripherals
     machine_pins_deinit();
+    machine_deinit();
     usocket_events_deinit();
 
     mp_deinit();

ports/esp32/modmachine.c

@@ -59,6 +59,8 @@ typedef enum {
     MP_SOFT_RESET
 } reset_reason_t;
 
+STATIC bool is_soft_reset = 0;
+
 STATIC mp_obj_t machine_freq(size_t n_args, const mp_obj_t *args) {
     if (n_args == 0) {
         // get
@@ -140,6 +142,9 @@ STATIC mp_obj_t machine_deepsleep(size_t n_args, const mp_obj_t *pos_args, mp_ma
 STATIC MP_DEFINE_CONST_FUN_OBJ_KW(machine_deepsleep_obj, 0,  machine_deepsleep);
 
 STATIC mp_obj_t machine_reset_cause(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
+    if (is_soft_reset) {
+        return MP_OBJ_NEW_SMALL_INT(MP_SOFT_RESET);
+    }
     switch (esp_reset_reason()) {
         case ESP_RST_POWERON:
         case ESP_RST_BROWNOUT:
@@ -171,6 +176,15 @@ STATIC mp_obj_t machine_reset_cause(size_t n_args, const mp_obj_t *pos_args, mp_
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_KW(machine_reset_cause_obj, 0,  machine_reset_cause);
 
+void machine_init(void) {
+    is_soft_reset = 0;
+}
+
+void machine_deinit(void) {
+    // we are doing a soft-reset so change the reset_cause
+    is_soft_reset = 1;
+}
+
 STATIC mp_obj_t machine_wake_reason(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
     return MP_OBJ_NEW_SMALL_INT(esp_sleep_get_wakeup_cause());
 }

ports/esp32/modmachine.h

@@ -22,6 +22,8 @@ extern const mp_obj_type_t machine_uart_type;
 extern const mp_obj_type_t machine_rtc_type;
 extern const mp_obj_type_t machine_sdcard_type;
 
+void machine_init(void);
+void machine_deinit(void);
 void machine_pins_init(void);
 void machine_pins_deinit(void);
 void machine_timer_deinit_all(void);