Bus fault on nRF52840 peripheral in BLE HCI USB Raw mode with 251-byte packets

RE: Bus fault on nRF52840 peripheral in BLE HCI USB Raw mode with 251-byte packets

Kenneth — Tue, 06 Jan 2026 08:41:11 GMT

Hi,

As a first step, make sure to only follow the description:
https://docs.nordicsemi.com/bundle/ncs-latest/page/zephyr/samples/bluetooth/hci_uart/README.html#using_a_usb_cdc_acm_uart

Looks like it resets, like due to an assert. Try to enable the following for more information about the assert:

CONFIG_ASSERT=y
CONFIG_ASSERT_VERBOSE=y
CONFIG_ASSERT_NO_COND_INFO=n
CONFIG_ASSERT_NO_MSG_INFO=n
CONFIG_RESET_ON_FATAL_ERROR=n

Best regards,
Kenneth

RE: Bus fault on nRF52840 peripheral in BLE HCI USB Raw mode with 251-byte packets

SaleemN — Wed, 31 Dec 2025 16:48:50 GMT

Hello,

I tried using HCI UART with USB CDC ACM UART (HCI UART). My hardware only supports USB, so I added CONFIG_CDC_ACM_SERIAL_PRODUCT_STRING to enable a virtual UART over USB. Below is the complete configuration used in the prj.conf file. However, I do not see any UART device on the host (for example, /dev/ttyACM*). Am I missing anything?”

Environment:

Host OS: Yocto-based Linux v6.6-scarthgap
Bluetooth stack: BlueZ v5.72

Settings:

CONFIG_CONSOLE=n

CONFIG_STDOUT_CONSOLE=n

CONFIG_UART_CONSOLE=n

CONFIG_GPIO=y

#CONFIG_SERIAL=y

CONFIG_UART_INTERRUPT_DRIVEN=y

CONFIG_BT=y

CONFIG_BT_HCI_RAW=y

CONFIG_BT_HCI_RAW_H4=y

CONFIG_BT_HCI_RAW_H4_ENABLE=y

CONFIG_BT_BUF_ACL_RX_SIZE=255

CONFIG_BT_BUF_CMD_TX_SIZE=255

CONFIG_BT_BUF_EVT_DISCARDABLE_SIZE=255

CONFIG_BT_CTLR_ASSERT_HANDLER=y

CONFIG_BT_MAX_CONN=16

#CONFIG_BT_CTLR_DTM_HCI=y

CONFIG_CDC_ACM_SERIAL_PRODUCT_STRING="Zephyr HCI UART sample"

CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=512

CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=y

I see the following log with RTT Viewer.

RE: Bus fault on nRF52840 peripheral in BLE HCI USB Raw mode with 251-byte packets

Kenneth — Mon, 29 Dec 2025 10:56:50 GMT

Hello,

The hci_usb is not stable, so please use hci_uart but with usb cdc as transport layer:
https://docs.nordicsemi.com/bundle/ncs-latest/page/zephyr/samples/bluetooth/hci_uart/README.html#using_a_usb_cdc_acm_uart

Kenneth