This fork of the Zephyr HCI UART example adds a custom HCI Command to allow for timesync between the Bluetooth Host and the Bluetooth Controller. When the HCI LE Read ISO Clock command is received, the Controller toggles a GPIO and returns its current Bluetooth LE ISO Clock in the Command Complete Event.

It has been tested on the nRF5340 Audio DK, but it should work with any nRF5340 dev kit.

HCI LE Read ISO Clock Command

OGF: 0x3f, OCF: 0x200
Parameters: Flags (1 Octet) unused
Response: HCI Command Complete Event with status and 4 bytes timestamp in microseconds

nRF5340 Development Kit

HCI over USB CDC

west build -b nrf5340dk_nrf5340_cpuapp -- -DEXTRA_DTC_OVERLAY_FILE=usb.overlay -DOVERLAY_CONFIG=overlay-usb.conf

HCI over UART and timesync not tested.

nRF5340 Audio DK

HCI over USB CDC

west build -b nrf5340_audio_dk_nrf5340_cpuapp -- -DEXTRA_DTC_OVERLAY_FILE=usb.overlay -DOVERLAY_CONFIG=overlay-usb.conf

HCI over UART 0 connected to Virtual UART in J-Link Probe

west build -b nrf5340_audio_dk_nrf5340_cpuapp

HCI over UART 1 connected to Virtual UART in J-Link Probe as well as Arduino Headers

Release build:

west build -b nrf5340_audio_dk_nrf5340_cpuapp -- -DEXTRA_DTC_OVERLAY_FILE=uart1.overlay

Debug build:

west build -b nrf5340_audio_dk_nrf5340_cpuapp -- -DEXTRA_DTC_OVERLAY_FILE=uart1.overlay -DOVERLAY_CONFIG=debug.conf

To use UART 1 via Arduino headers, the virtual UART of the J-Link probe needs to be disabled, e.g. with the JLink Configuration Tool.

UART 1 + Time Sync Pinout

Signal direction as seen from the nRF5340.

PIN	Arduino	nrf	Direction
TX	D0	P1.09	out
RX	D1	P1.08	in
RTS	D7	P1.11	out
CTS	D8	P1.10	in
Timesync	D10	P1.01	out