pbio/os: Add API for extending timeout by interval.

This makes it possible to have processes have constant loop time on average.

Fixes pybricks/support#2282

Author: laurensvalk

lib/pbio/include/pbio/os.h

@@ -71,6 +71,8 @@ typedef struct pbio_os_timer_t {
 
 void pbio_os_timer_set(pbio_os_timer_t *timer, uint32_t duration);
 
+void pbio_os_timer_extend(pbio_os_timer_t *timer);
+
 bool pbio_os_timer_is_expired(pbio_os_timer_t *timer);
 
 /**

lib/pbio/src/os.c

@@ -24,6 +24,17 @@ void pbio_os_timer_set(pbio_os_timer_t *timer, uint32_t duration) {
     timer->duration = duration;
 }
 
+/**
+ * Extends the timeout by incrementing the start time by the duration.
+ *
+ * Duration must have been set by ::pbio_os_timer_set previously.
+ *
+ * @param timer     The timer whose timeout to extend.
+ */
+void pbio_os_timer_extend(pbio_os_timer_t *timer) {
+    timer->start += timer->duration;
+}
+
 /**
  * Whether the timer has expired.
  *