codal_port: Add mp_sched_schedule_exception helper and use it.

Signed-off-by: Damien George <damien@micropython.org>

Author: dpgeorge

src/codal_port/drv_display.c

@@ -93,7 +93,7 @@ static void draw_object(mp_obj_t obj) {
             async_stop();
         }
     } else {
-        MP_STATE_VM(mp_pending_exception) = mp_obj_new_exception_msg(&mp_type_TypeError, "not an image");
+        mp_sched_schedule_exception(mp_obj_new_exception_msg(&mp_type_TypeError, "not an image"));
         async_stop();
     }
 }
@@ -126,7 +126,7 @@ void microbit_display_update(void) {
                     if (mp_obj_get_type(nlr.ret_val) == &mp_type_MemoryError) {
                         mp_printf(&mp_plat_print, "Allocation in interrupt handler");
                     }
-                    MP_STATE_VM(mp_pending_exception) = MP_OBJ_FROM_PTR(nlr.ret_val);
+                    mp_sched_schedule_exception(MP_OBJ_FROM_PTR(nlr.ret_val));
                 }
                 obj = MP_OBJ_STOP_ITERATION;
             }

src/codal_port/modaudio.c

@@ -77,7 +77,7 @@ STATIC void audio_data_fetcher(void) {
     } else {
         if (!mp_obj_is_subclass_fast(MP_OBJ_FROM_PTR(((mp_obj_base_t*)nlr.ret_val)->type),
             MP_OBJ_FROM_PTR(&mp_type_StopIteration))) {
-            MP_STATE_VM(mp_pending_exception) = MP_OBJ_FROM_PTR(nlr.ret_val);
+            mp_sched_schedule_exception(MP_OBJ_FROM_PTR(nlr.ret_val));
         }
         buffer_obj = MP_OBJ_STOP_ITERATION;
     }
@@ -89,7 +89,7 @@ STATIC void audio_data_fetcher(void) {
         // Audio iterator did not return an AudioFrame
         audio_source_iter = NULL;
         microbit_audio_stop();
-        MP_STATE_VM(mp_pending_exception) = mp_obj_new_exception_msg(&mp_type_TypeError, "not an AudioFrame");
+        mp_sched_schedule_exception(mp_obj_new_exception_msg(&mp_type_TypeError, "not an AudioFrame"));
     } else {
         microbit_audio_frame_obj_t *buffer = (microbit_audio_frame_obj_t *)buffer_obj;
         uint8_t *dest = &audio_output_buffer[0];

src/codal_port/mphalport.c

@@ -27,6 +27,13 @@
 #include "py/runtime.h"
 #include "py/mphal.h"
 
+void mp_sched_schedule_exception(mp_obj_t exc) {
+    MP_STATE_VM(mp_pending_exception) = exc;
+    if (MP_STATE_VM(sched_state) == MP_SCHED_IDLE) {
+        MP_STATE_VM(sched_state) = MP_SCHED_PENDING;
+    }
+}
+
 void mp_hal_delay_us(mp_uint_t us) {
     if (us <= 0) {
         return;

src/codal_port/mphalport.h

@@ -24,11 +24,13 @@
  * THE SOFTWARE.
  */
 
+#include "py/obj.h"
 #include "microbithal.h"
 
 // Not implemented and not exposed in utime module.
 #define mp_hal_ticks_cpu() (0)
 
+void mp_sched_schedule_exception(mp_obj_t exc);
 void mp_hal_set_interrupt_char(int c);
 
 // MicroPython low-level C API for pins