bricks/stm32: Force exit on shutdown.

Since the removal of the longjump in 6d06933,
the user could prevent the hub from stopping the program and shutting down
by catching all exceptions.

This commit ensures we can force a safe exit on shutdown in all cases.

bricks/_common/micropython.c

@@ -32,19 +32,33 @@
 #include "py/stackctrl.h"
 #include "py/stream.h"
 
+// Outermost nlr buffer.
+nlr_buf_t nlr_main;
+
 // Implementation for MICROPY_EVENT_POLL_HOOK
 void pb_event_poll_hook(void) {
     while (pbio_do_one_event()) {
     }
 
+    // On forced exit, pop back to outer nlr buffer so the exception will
+    // always be raised and the application program exits cleanly. We also need
+    // MP_STATE_THREAD(mp_pending_exception) to be the system exit exception
+    // but we don't check it because it is set along with pyexec_system_exit.
+    if (pyexec_system_exit == PYEXEC_FORCED_EXIT) {
+        while (MP_STATE_MAIN_THREAD(nlr_top) != &nlr_main) {
+            nlr_pop();
+        }
+        pyexec_system_exit = 0;
+    }
+
     mp_handle_pending(true);
 
     // Platform-specific code to run on completing the poll hook.
     pb_event_poll_hook_leave();
 }
 
 // callback for when stop button is pressed in IDE or on hub
-void pbsys_main_stop_program(void) {
+void pbsys_main_stop_program(bool force_stop) {
 
     static const mp_obj_tuple_t args = {
         .base = { .type = &mp_type_tuple },
@@ -53,9 +67,6 @@ void pbsys_main_stop_program(void) {
     };
     static mp_obj_exception_t system_exit;
 
-    // Trigger soft reboot.
-    pyexec_system_exit = PYEXEC_FORCED_EXIT;
-
     // Schedule SystemExit exception.
     system_exit.base.type = &mp_type_SystemExit;
     system_exit.traceback_alloc = 0;
@@ -68,6 +79,11 @@ void pbsys_main_stop_program(void) {
         MP_STATE_VM(sched_state) = MP_SCHED_PENDING;
     }
     #endif
+
+    // IDE stop button and long-press power button will force an exit.
+    if (force_stop) {
+        pyexec_system_exit = PYEXEC_FORCED_EXIT;
+    }
 }
 
 bool pbsys_main_stdin_event(uint8_t c) {
@@ -112,16 +128,15 @@ static void mp_vfs_map_minimal_new_reader(mp_reader_t *reader, mp_vfs_map_minima
 static void run_repl() {
     // Reset REPL history.
     readline_init0();
-    nlr_buf_t nlr;
-    if (nlr_push(&nlr) == 0) {
+    if (nlr_push(&nlr_main) == 0) {
         // Run the REPL.
         pyexec_friendly_repl();
         nlr_pop();
     } else {
         // clear any pending exceptions (and run any callbacks).
         mp_handle_pending(false);
         // Print which exception triggered this.
-        mp_obj_print_exception(&mp_plat_print, (mp_obj_t)nlr.ret_val);
+        mp_obj_print_exception(&mp_plat_print, (mp_obj_t)nlr_main.ret_val);
     }
 }
 #endif
@@ -209,8 +224,7 @@ static mpy_info_t *mpy_data_find(qstr name) {
  */
 static void run_user_program(void) {
 
-    nlr_buf_t nlr;
-    if (nlr_push(&nlr) == 0) {
+    if (nlr_push(&nlr_main) == 0) {
         mpy_info_t *info = mpy_data_find(MP_QSTR___main__);
 
         if (!info) {
@@ -241,11 +255,11 @@ static void run_user_program(void) {
         mp_handle_pending(false);
 
         // Print which exception triggered this.
-        mp_obj_print_exception(&mp_plat_print, (mp_obj_t)nlr.ret_val);
+        mp_obj_print_exception(&mp_plat_print, (mp_obj_t)nlr_main.ret_val);
 
         #if PYBRICKS_OPT_COMPILER
         // On KeyboardInterrupt, drop to REPL for debugging.
-        if (mp_obj_exception_match((mp_obj_t)nlr.ret_val, &mp_type_KeyboardInterrupt)) {
+        if (mp_obj_exception_match((mp_obj_t)nlr_main.ret_val, &mp_type_KeyboardInterrupt)) {
 
             // The global scope is preserved to facilitate debugging, but we
             // stop active resources like motors and sounds. They are stopped

bricks/virtualhub/mp_port.c

@@ -34,7 +34,7 @@
 #define FORCED_EXIT (0x100)
 
 // callback for when stop button is pressed in IDE or on hub
-void pbsys_main_stop_program(void) {
+void pbsys_main_stop_program(bool force_stop) {
     static const mp_rom_obj_tuple_t args = {
         .base = { .type = &mp_type_tuple },
         .len = 2,

lib/pbio/include/pbsys/main.h

@@ -52,8 +52,12 @@ void pbsys_main_run_program(pbsys_main_program_t *program);
  * Stops (cancels) the main application program.
  *
  * This should be provided by the application running on top of pbio.
+ *
+ * @param [in]  force_stop  Whether to force stop the program instead of asking
+ *                          nicely. This is true when the application must stop
+ *                          on shutdown.
  */
-void pbsys_main_stop_program(void);
+void pbsys_main_stop_program(bool force_stop);
 
 /**
  * Handles standard input.
@@ -68,7 +72,7 @@ bool pbsys_main_stdin_event(uint8_t c);
 
 #else
 
-static inline void pbsys_main_stop_program(void) {
+static inline void pbsys_main_stop_program(bool force_stop) {
 }
 
 static inline bool pbsys_main_stdin_event(uint8_t c) {

lib/pbio/sys/command.c

@@ -23,7 +23,7 @@ pbio_pybricks_error_t pbsys_command(const uint8_t *data, uint32_t size) {
 
     switch (cmd) {
         case PBIO_PYBRICKS_COMMAND_STOP_USER_PROGRAM:
-            pbsys_program_stop();
+            pbsys_program_stop(false);
             return PBIO_PYBRICKS_ERROR_OK;
         case PBIO_PYBRICKS_COMMAND_START_USER_PROGRAM:
             return pbio_pybricks_error_from_pbio_error(pbsys_program_load_start_user_program());

lib/pbio/sys/program_stop.c

@@ -22,10 +22,14 @@ static bool program_stop_on_shutdown_requested;
 /**
  * Request the user program to stop. For example, in MicroPython, this may raise
  * a SystemExit exception.
+ *
+ * @param [in]  force_stop  Whether to force stop the program instead of asking
+ *                          nicely. This is true when the application must stop
+ *                          on shutdown.
  */
-void pbsys_program_stop(void) {
+void pbsys_program_stop(bool force_stop) {
     if (pbsys_status_test(PBIO_PYBRICKS_STATUS_USER_PROGRAM_RUNNING)) {
-        pbsys_main_stop_program();
+        pbsys_main_stop_program(force_stop);
     }
 }
 
@@ -48,7 +52,7 @@ void pbsys_program_stop_poll(void) {
         // Should not request stop more than once.
         return;
     } else if (pbsys_status_test(PBIO_PYBRICKS_STATUS_SHUTDOWN_REQUEST)) {
-        pbsys_program_stop();
+        pbsys_program_stop(true);
         program_stop_on_shutdown_requested = true;
         return;
     }
@@ -63,7 +67,7 @@ void pbsys_program_stop_poll(void) {
     if ((btn & stop_buttons) == stop_buttons) {
         if (!stop_button_pressed) {
             stop_button_pressed = true;
-            pbsys_program_stop();
+            pbsys_program_stop(false);
         }
     } else {
         stop_button_pressed = false;

lib/pbio/sys/program_stop.h

@@ -5,6 +5,6 @@
 #define _PBSYS_SYS_USER_PROGRAM_H_
 
 void pbsys_program_stop_poll(void);
-void pbsys_program_stop(void);
+void pbsys_program_stop(bool force_stop);
 
 #endif // _PBSYS_SYS_USER_PROGRAM_H_