bricks/_common/micropython: Flush stdout on completion.

Ensures we don't send the program stopped status before the program is truly done.

In turn, this ensures that a new program can't be started before stdout from the last program is one.

Author: laurensvalk

bricks/_common/micropython.c

@@ -406,6 +406,10 @@ void pbsys_main_run_program(pbsys_main_program_t *program) {
             run_user_program();
             break;
     }
+
+    // Ensure everything is written before the user application is considered
+    // done, so that the host does not receive stdout after receiving stop.
+    mp_hal_stdout_tx_flush();
 }
 
 void pbsys_main_run_program_cleanup(void) {

bricks/_common/mphalport.c

@@ -71,6 +71,7 @@ mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
             return len - remaining;
         }
 
+        // May raise, so long print can be stopped.
         MICROPY_EVENT_POLL_HOOK
     }
 
@@ -79,6 +80,7 @@ mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
 
 void mp_hal_stdout_tx_flush(void) {
     while (!pbsys_host_tx_is_idle()) {
-        MICROPY_EVENT_POLL_HOOK
+        // Don't raise, just wait for data to clear.
+        MICROPY_VM_HOOK_LOOP;
     }
 }