SoftDevice Controller: Scanner window gets truncated/cancelled during concurrent Advertiser activity on nRF54LM20 (NCS v3.3.1)

Question

Subject: SoftDevice Controller: Scanner window gets truncated/cancelled during concurrent Advertiser activity on nRF54LM20 (NCS v3.3.1) Description: Environment: Board: nRF54LM20 DK SDK: nRF Connect SDK v3.3.1 Stack: SoftDevice Controller (default) Role: Concurrent Advertiser (Connectable) + Scanner (No connection) Configuration: CONFIG_BT_PERIPHERAL=y CONFIG_BT_OBSERVER=y CONFIG_BT_CENTRAL=y (Required for bt_scan library compilation) Advertising: BT_LE_ADV_CONN_FAST_1 , interval 30–60 ms (randomized) Scanning: Passive scan via Nordic bt_scan API, using default parameters: scan interval = 60 ms, scan window = 30 ms . A non-existent MAC address is used as a filter so it never matches/connects. Connection interval: When a central device connects to us (we are the Peripheral), we request a connection interval of 60 ms via bt_conn_le_param_update() . Therefore, once connected, connection events occur every 60 ms and can also preempt the Scanner's RX window. Problem Description: I am running a dual-role application (Advertiser + Scanner). When monitoring power consumption, I observe that the Scanner RX window (approx. 4-5mA) starts, but gets abruptly truncated by TX spikes (approx. 15mA) around the 15ms mark. The scanner window does not resume after the TX spike; instead, it waits for the next scan interval. The interruption appears to be caused by the Advertiser's TX activity, which may be either an advertising event or a connection event (if a central device has connected to us, with a 60 ms connection interval). [Please see the attached power profiler waveform showing the interruption] Questions: The documentation states: "The timing-activities run to completion and cannot be preempted by other timing-activities, even if the timing-activity trying to preempt has a higher priority." However, my power profiler waveform shows that the Scanner RX window (approx. 4-5mA) has already been running for ~15ms when it gets abruptly truncated by the Advertiser TX spikes (approx. 15mA). How does the SoftDevice Controller define "already started"? Is it at the moment the radio starts receiving, or at the moment the scheduler officially locks the radio resource? Why does an event that appears to have already started still get truncated? The documentation states: "Activity B will be blocked and its timing-event will be rescheduled for a later time." However, in my observation, the Scanner window is not "blocked and rescheduled" — it is directly terminated, and the remaining 15ms is discarded. The scanner does not resume after the TX spike; it waits for the next scan interval. Does "rescheduled for a later time" mean the next scan interval (i.e., the entire window is discarded), or does it mean the remaining window time should be resumed? CONFIG_BT=y CONFIG_BT_PERIPHERAL=y CONFIG_BT_OBSERVER=y CONFIG_BT_DEVICE_NAME="DualRole" CONFIG_BT_SCAN=y CONFIG_BT_SCAN_FILTER_ENABLE=y CONFIG_BT_SCAN_UUID_CNT=1 CONFIG_BT_CENTRAL=y CONFIG_SERIAL=n CONFIG_UART_CONSOLE=n CONFIG_PRINTK=n #include #include #include #include #include /* ========== Advertising data ========== */ static const struct bt_data ad[] = { BT_DATA_BYTES(BT_DATA_FLAGS, (BT_LE_AD_GENERAL | BT_LE_AD_NO_BREDR)), BT_DATA(BT_DATA_NAME_COMPLETE, CONFIG_BT_DEVICE_NAME, sizeof(CONFIG_BT_DEVICE_NAME) - 1), }; /* ========== Connection callbacks ========== */ static void connected(struct bt_conn *conn, uint8_t err) { if (err) { return; } /* Connection established. No action needed here. */ } static void disconnected(struct bt_conn *conn, uint8_t reason) { struct bt_conn_info info; bt_conn_get_info(conn, &info); /* Restart connectable advertising when the peripheral role disconnects */ if (info.role == BT_CONN_ROLE_PERIPHERAL) { bt_le_adv_start(BT_LE_ADV_CONN_FAST_1, ad, ARRAY_SIZE(ad), NULL, 0); } } BT_CONN_CB_DEFINE(conn_callbacks) = { .connected = connected, .disconnected = disconnected, }; /* ========== Advertising start ========== */ static void adv_start(void) { bt_le_adv_start(BT_LE_ADV_CONN_FAST_1, ad, ARRAY_SIZE(ad), NULL, 0); } /* ========== Scan callbacks (empty, placeholders only) ========== */ static void scan_filter_match(struct bt_scan_device_info *device_info, struct bt_scan_filter_match *filter_match, bool connectable) { (void)device_info; (void)filter_match; (void)connectable; } static void scan_connecting_error(struct bt_scan_device_info *device_info) { (void)device_info; } static void scan_connecting(struct bt_scan_device_info *device_info, struct bt_conn *conn) { (void)device_info; (void)conn; } BT_SCAN_CB_INIT(scan_cb, scan_filter_match, NULL, scan_connecting_error, scan_connecting); /* ========== Scan initialization ========== */ static void scan_init(void) { /* Non-existent MAC address, so the filter never matches */ static const bt_addr_le_t target_addr = { .type = BT_ADDR_LE_PUBLIC, .a = { { 0xDE, 0xAD, 0xBE, 0xEF, 0x00, 0x01 } }, }; struct bt_scan_init_param param = { .scan_param = NULL, /* Use default scan parameters */ .conn_param = BT_LE_CONN_PARAM_DEFAULT, .connect_if_match = 1, /* Auto-connect enabled, but filter never matches */ }; bt_scan_init(¶m); bt_scan_cb_register(&scan_cb); /* Add address filter (never matches) */ bt_scan_filter_add(BT_SCAN_FILTER_TYPE_ADDR, (void *)&target_addr); bt_scan_filter_enable(BT_SCAN_ADDR_FILTER, false); } /* ========== Main ========== */ int main(void) { int err; err = bt_enable(NULL); if (err) { return 0; } /* Start connectable advertising (Peripheral role) */ adv_start(); /* Initialize scan module and start continuous scanning */ scan_init(); err = bt_scan_start(BT_SCAN_TYPE_SCAN_PASSIVE); if (err) { return 0; } while (1) { k_sleep(K_FOREVER); } return 0; }