pbsys/status: add status report size macro

The size of the status report may change in the future, so add a macro
to help catch other places in the code that may need to be updated when
the size changes.

Author: dlech

lib/pbio/include/pbsys/status.h

@@ -14,6 +14,8 @@
 
 #include <pbio/protocol.h>
 
+#define PBSYS_STATUS_REPORT_SIZE 6
+
 void pbsys_status_set_program_id(pbio_pybricks_user_program_id_t program_id);
 void pbsys_status_set(pbio_pybricks_status_t status);
 void pbsys_status_clear(pbio_pybricks_status_t status);

lib/pbio/sys/bluetooth.c

@@ -269,6 +269,7 @@ static PT_THREAD(pbsys_bluetooth_monitor_status(struct pt *pt)) {
         etimer_restart(&timer);
 
         // send the message
+        _Static_assert(sizeof(msg.payload) >= PBIO_PYBRICKS_EVENT_STATUS_REPORT_SIZE);
         msg.context.size = pbsys_status_get_status_report(&msg.payload[0]);
         msg.context.connection = PBDRV_BLUETOOTH_CONNECTION_PYBRICKS;
         list_add(send_queue, &msg);

lib/pbio/sys/status.c

@@ -38,12 +38,16 @@ static void pbsys_status_update_flag(pbio_pybricks_status_t status, bool set) {
 }
 
 /**
- * Gets the Pybricks status report and writes it to @p buf
+ * Gets the Pybricks status report and writes it to @p buf.
+ *
+ * The buffer must be at least ::PBSYS_STATUS_REPORT_SIZE bytes.
  *
  * @param [in]  buf        The buffer to hold the binary data.
  * @return                 The number of bytes written to @p buf.
  */
 uint32_t pbsys_status_get_status_report(uint8_t *buf) {
+    _Static_assert(PBSYS_STATUS_REPORT_SIZE == PBIO_PYBRICKS_EVENT_STATUS_REPORT_SIZE,
+        "size of status report does not match size of event");
     return pbio_pybricks_event_status_report(buf, pbsys_status.flags, pbsys_status.program_id);
 }