movement: prevent invalid tick frequency from breaking scheduled tasks

2 files changed, 7 insertions, 4 deletions

diff --git a/movement/movement.c b/movement/movement.c
index aa95f2f1..42b73526 100644
--- a/movement/movement.c
+++ b/movement/movement.c
@@ -152,14 +152,19 @@ static void _movement_handle_scheduled_tasks(void) {
 }
 
 void movement_request_tick_frequency(uint8_t freq) {
-    if (freq == 128) return; // Movement uses the 128 Hz tick internally
+    // Movement uses the 128 Hz tick internally
+    if (freq == 128) return;
+
+    // Movement requires at least a 1 Hz tick.
+    // If we are asked for an invalid frequency, default back to 1 Hz.
+    if (freq == 0 || __builtin_popcount(freq) != 1) freq = 1;
 
     // disable all callbacks except the 128 Hz one
     watch_rtc_disable_matching_periodic_callbacks(0xFE);
 
     movement_state.subsecond = 0;
     movement_state.tick_frequency = freq;
-    if (freq) watch_rtc_register_periodic_callback(cb_tick, freq);
+    watch_rtc_register_periodic_callback(cb_tick, freq);
 }
 
 void movement_illuminate_led(void) {
diff --git a/movement/movement.h b/movement/movement.h
index 8949d026..cb2c9ca2 100644
--- a/movement/movement.h
+++ b/movement/movement.h
@@ -274,8 +274,6 @@ void movement_move_to_face(uint8_t watch_face_index);
 void movement_move_to_next_face(void);
 void movement_illuminate_led(void);
 
-// note: requesting a tick frequency of 0 will break any scheduled background tasks.
-// this will be fixed in a future refactor of the tick mechanism.
 void movement_request_tick_frequency(uint8_t freq);
 
 // note: watch faces can only schedule a background task when in the foreground, since