applications: nrf_desktop: Introduce forced scan state

Change introduces forced scan state. In this state scanning is not
interrupted by HID data transmission to host. The new state speeds up
connection establishment.

Jira: NCSDK-20843

Signed-off-by: Marek Pieta <Marek.Pieta@nordicsemi.no>

applications/nrf_desktop/src/modules/Kconfig.ble_scan

@@ -45,6 +45,16 @@ config DESKTOP_BLE_SCAN_DURATION_S
  help
  After this time scan is disabled if any peripheral is connected.
 
+config DESKTOP_BLE_FORCED_SCAN_DURATION_S
+ int "Forced scan duration [s]"
+ default 4
+ help
+ Duration of the forced scan operation in seconds. The module enters a
+ forced scan state right after boot or wakeup, on successful peripheral
+ discovery, on peripheral disconnection and on connection failure.
+
+ Setting forced scan duration to 0 disables the feature.
+
 config DESKTOP_BLE_SCAN_MOUSE_LIMIT
  int "Maximum number of bonded mice"
  default 1

applications/nrf_desktop/src/modules/ble_scan.c

@@ -27,11 +27,13 @@ LOG_MODULE_REGISTER(MODULE, CONFIG_DESKTOP_BLE_SCAN_LOG_LEVEL);
 #define SCAN_START_CHECK_MS (1 * MSEC_PER_SEC)
 #define SCAN_START_TIMEOUT_MS (CONFIG_DESKTOP_BLE_SCAN_START_TIMEOUT_S * MSEC_PER_SEC)
 #define SCAN_DURATION_MS (CONFIG_DESKTOP_BLE_SCAN_DURATION_S * MSEC_PER_SEC)
+#define FORCED_SCAN_DURATION_MS (CONFIG_DESKTOP_BLE_FORCED_SCAN_DURATION_S * MSEC_PER_SEC)
 #define SCAN_START_DELAY_MS 15
 
 BUILD_ASSERT(SCAN_START_CHECK_MS > 0);
 BUILD_ASSERT(SCAN_START_TIMEOUT_MS > 0);
 BUILD_ASSERT(SCAN_DURATION_MS > 0, "");
+BUILD_ASSERT(FORCED_SCAN_DURATION_MS >= 0, "");
 BUILD_ASSERT(SCAN_START_DELAY_MS > 0, "");
 
 #define SUBSCRIBED_PEERS_STORAGE_NAME "subscribers"
@@ -42,6 +44,7 @@ enum state {
  STATE_INITIALIZED,
  STATE_INITIALIZED_OFF,
  STATE_ACTIVE,
+ STATE_FORCED_ACTIVE,
  STATE_DELAYED_ACTIVE,
  STATE_INACTIVE,
  STATE_OFF,
@@ -534,6 +537,9 @@ static const char *state2str(enum state s)
  case STATE_ACTIVE:
  return "ACTIVE";
 
+ case STATE_FORCED_ACTIVE:
+ return "FORCED_ACTIVE";
+
  case STATE_DELAYED_ACTIVE:
  return "DELAYED_ACTIVE";
 
@@ -557,7 +563,12 @@ static enum state update_state_transition(enum state prev_state, enum state new_
  size_t conn_count = count_conn();
  size_t bond_count = count_bond();
 
- if (new_state == STATE_ACTIVE) {
+ /* Skip forced active state if disabled in configuration. */
+ if ((new_state == STATE_FORCED_ACTIVE) && (FORCED_SCAN_DURATION_MS == 0)) {
+ new_state = STATE_ACTIVE;
+ }
+
+ if ((new_state == STATE_ACTIVE) || (new_state == STATE_FORCED_ACTIVE)) {
  if (IS_ENABLED(CONFIG_DESKTOP_BLE_NEW_PEER_SCAN_REQUEST) &&
  (conn_count == bond_count) && peers_only) {
  if (verbose) {
@@ -626,6 +637,7 @@ static int update_scan_control(enum state prev_state, enum state new_state)
 
  switch (new_state) {
  case STATE_ACTIVE:
+ case STATE_FORCED_ACTIVE:
  err = scan_start();
  break;
 
@@ -656,6 +668,10 @@ static void update_work(enum state prev_state, enum state new_state)
  }
  break;
 
+ case STATE_FORCED_ACTIVE:
+ (void)k_work_reschedule(&update_state_work, K_MSEC(FORCED_SCAN_DURATION_MS));
+ break;
+
  case STATE_DELAYED_ACTIVE:
  (void)k_work_reschedule(&update_state_work, K_MSEC(SCAN_START_DELAY_MS));
  break;
@@ -723,10 +739,14 @@ static void update_state_work_fn(struct k_work *w)
  update_state(STATE_INACTIVE);
  break;
 
- case STATE_DELAYED_ACTIVE:
+ case STATE_FORCED_ACTIVE:
  update_state(STATE_ACTIVE);
  break;
 
+ case STATE_DELAYED_ACTIVE:
+ update_state(STATE_FORCED_ACTIVE);
+ break;
+
  case STATE_INACTIVE:
  scan_start_counter += SCAN_START_CHECK_MS;
  if (scan_start_counter >= SCAN_START_TIMEOUT_MS) {
@@ -757,7 +777,7 @@ static bool handle_hid_report_event(const struct hid_report_event *event)
  * avoid negatively affecting HID report rate.
  */
  scan_start_counter = 0;
- } else if ((state == STATE_ACTIVE) || (state == STATE_DELAYED_ACTIVE)) {
+ } else if (state == STATE_ACTIVE) {
  update_state(STATE_INACTIVE);
  }
 
@@ -790,7 +810,7 @@ static bool handle_module_state_event(const struct module_state_event *event)
  */
  switch (state) {
  case STATE_INITIALIZED:
- update_state(STATE_ACTIVE);
+ update_state(STATE_FORCED_ACTIVE);
  break;
 
  case STATE_INITIALIZED_OFF:
@@ -857,7 +877,7 @@ static bool handle_ble_peer_operation_event(const struct ble_peer_operation_even
  }
 
  if (state != STATE_OFF) {
- update_state(STATE_ACTIVE);
+ update_state(STATE_FORCED_ACTIVE);
  }
  break;
 
@@ -909,6 +929,7 @@ static bool handle_power_down_event(const struct power_down_event *event)
  case STATE_ACTIVE:
  case STATE_DELAYED_ACTIVE:
  case STATE_INACTIVE:
+ case STATE_FORCED_ACTIVE:
  update_state(STATE_OFF);
  break;
 
@@ -932,7 +953,7 @@ static bool handle_wake_up_event(const struct wake_up_event *event)
  break;
 
  case STATE_OFF:
- update_state(STATE_ACTIVE);
+ update_state(STATE_FORCED_ACTIVE);
  break;
 
  default: