Unable to establish communication between a nRF52840-Dongle, programmed with the HCI_uart example, and a Raspberry Pi 3 B+

[matt_C]

I am trying to use the BluePy Scanner on a Raspberry Pi 3 B+ with a nRF52840-Dongle programmed as a Bluetooth: HCI-uart.

I am able to get the Bluepy Scanner code to work with the onboard BLE, but I am so far unable to get it to communicate with the Bluetooth HCI dongle that is attached to the UART0 (/dev/ttyS0). I have connected UART0_TXD (GPIO14), UART0_RXD (GPIO15), UART0_CTS (GPIO16), and UART0_RTS (GPIO17).

How can I attach and use a nRF52840-Dongle, programmed with the HCI_uart example, with a Raspberry Pi 3 B+?

Following are my nrf52840dongle_nrf52840.overlay and proj.conf files for the HCI_uart.

nrf52840dongle_nrf52840.overlay

/* SPDX-License-Identifier: Apache-2.0 */

&uart0 {
	compatible = "nordic,nrf-uart";
	current-speed = <1000000>;
	status = "okay";
	tx-pin = <45>;
	rx-pin = <42>;
	rts-pin = <47>;
	cts-pin = <29>;
	hw-flow-control;
};

proj.conf

CONFIG_CONSOLE=n
CONFIG_STDOUT_CONSOLE=n
CONFIG_UART_CONSOLE=n
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_GPIO=y
CONFIG_UART_0_NRF_FLOW_CONTROL=y
CONFIG_MAIN_STACK_SIZE=1024
CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=512
CONFIG_BT_MAX_CONN=16
CONFIG_BT_TINYCRYPT_ECC=n
CONFIG_BT_CTLR_DTM_HCI=y
CONFIG_BT_CTLR_ASSERT_HANDLER=y

I following DT overlays in on my Raspberry Pi, uart_ctsrts and krnbt_baudrate=1000000.

From the command line I try 

btattach -B /dev/ttyS0 -P bcm -S 1000000 -R &

and I get the following message.

Attaching Primary controller to /dev/ttyS0
Switched line discipline from 0 to 15
Device index 1 attached
Failed to open HCI user channel
No controller attached

hciconfig status returns the following for the onboard BLE

hci0: Type: Primary Bus: UART
BD Address: B8:27:EB:EE:6C:BD ACL MTU: 1021:8 SCO MTU: 64:1
UP RUNNING
RX bytes:13508 acl:0 sco:0 events:562 errors:0
TX bytes:2402 acl:0 sco:0 commands:124 errors:0

However, when I use the HCI_USB example I see the hci1 entry for the dongle. I realize that the USB will auto mount, unlike ttyS0, this is just to evidence that the dongle is functional.

[JONATHAN LL]

Hi Matthew,

UART0_CTS (GPIO16)

The P016 is not connected to anything on the nrf52dongle, ref

So try changing it to one of the I/O that are accessible.

Regards,
Jonathan

[matt_C]

Sorry for the confusion. I am not connecting to P0.16 on the dongle. Following are my connections.

nRF52840-Dongle			Raspberry Pi 3 B+
Signal	Pin		Signal	BCM Pin	40-pin header pin
RX	P1.10	<—->	TXD0	GPIO14	8
TX	P1.13	<—->	RXD0	GPIO15	10
CTS	P0.29	<—->	CTS0	GPIO16	36
RTS	P1.15	<—->	RTS0	GPIO17	11

Following is my Zephyr device tree overlay for the nRF52840-Dongle.

/* SPDX-License-Identifier: Apache-2.0 */

&uart0 {

    compatible = "nordic,nrf-uart";

    current-speed = <1000000>;

    status = "okay";

    tx-pin = <45>;

    rx-pin = <42>;

    rts-pin = <47>;

    cts-pin = <29>;

    hw-flow-control;

};

[JONATHAN LL]

Hi Matthew sorry for the late reply,
What you have done seems to be correct for the dongle, but I would recommend testing whit a lower baud rate. 
Alternatively here is a link to a blog post for Linux use. I think maybe the problem is on the RPi side of things, I don't ha a RPi to test right now but can try to get a old of one an se if i can reproduce the error. 
Have you checked out the RPi forum to see if there are some similar cases? I vas able to find this one, maybe it helps?
Regards,
Jonathan

[matt_C]

I will look over the links you sent.

Where do I need to modify the HCI UART example to set the lower baud rate, since 1Mbit/s is the default uart setting?

I haven't tried the RPi forum, but I have made the following post on the Balena forums. forums.balena.io/.../193535

[matt_C]

I agree that the problem is most likely on the RPi side of things, I am hoping that the testing that was done by Nordic to validate the HCI_UART can help illuminate how I can make It work with the RPi.

Following is my post to the RPi forum, https://www.raspberrypi.org/forums/viewtopic.php?f=28&t=287232 

[JONATHAN LL]

Hi,

To change the baud rate edit this; current-speed = <Baud Rate>;  in the overlay file.

I will test it out and se if i am able to find a solution, it might take some time as i don't have a RPi atm. 
I will update you on any progress. 


Do you have any other 52 devices? a 52DK or something that you could test with maybe ?

Regards,
Jonathan

[matt_C]

I have an nRF52840-DK I could test with. Do you have a sample project that would use the nRF52840-Dongle HCI_UART as a peripheral?

Thanks,

Matt

[JONATHAN LL]

I was thinking that you could use the nrf52-dk instead of the dongle. try to use the I/O pins on the dk and connect it to the RPi's GPIO in the same way you tired the dongle. Then you could see if the same behaviour happens with the 52-dk. if so then i think we can assume its on the RPi side and try something else  

Here are some hopefully helpful links:
https://devzone.nordicsemi.com/f/nordic-q-a/39998/maximum-number-of-ble-slaves-with-rpi-master
https://github.com/NordicSemiconductor/pc-ble-driver
https://devzone.nordicsemi.com/f/nordic-q-a/17783/nrf52832-hci-firmware
https://devzone.nordicsemi.com/f/nordic-q-a/39106/nrf52840-dongle-to-raspberry-pi-b
https://github.com/nicslabdev/NRF52840-Beacon_Scanner

We do not have a sample project other than HCI_UART in the nrf-connect-sdk. 
Regards,
Jonathan