Thingy91 connections between 9160 and 52840

[dboling]

I would like to program the 52840 with the HCI_UART sample to use it for Bluetooth scanning. I did this and lost the USB serial out.  I now understand that on the Thingy91, the '840 is used as a board controller and that serial communication is relayed from the 9160 through to the USB port.  I found the code for the UART / USB bridge and was able to restore the USB serial comm.

I would like to combine the two samples so that I can use Bluetooth, while retaining the USB serial out. The problem is parsing the serial out data vs the bluetooth commands.

I'm trying to determine the UART connections between the two chips. Are both UART0 and UART1 on the 9160 connected to the 52840 or just one?  I've scanned the schematics but the flexibility of the I/O on the chips makes it it a bit complex. A bit of help on the connectivity would save me a fair amount of reverse engineering.  Thanks.

Doug

[Håkon Alseth]

Hi,

 

This is the sample that does the usb-to-uart bridging on the nRF52840 located on the thingy:91:

https://github.com/NordicPlayground/fw-nrfconnect-nrf/tree/master/samples/usb/usb_uart_bridge

This one is connected via the pins labeled "MCU_IF0" to "MCU_IF7", and you can use the dts file to see how its mapped between nRF91 and nRF52840:

nRF52840: https://github.com/NordicPlayground/fw-nrfconnect-nrf/blob/master/boards/arm/nrf52840_pca20035/nrf52840_pca20035.dts#L39

nRF9160: https://github.com/NordicPlayground/fw-nrfconnect-nrf/blob/master/boards/arm/nrf9160_pca20035/nrf9160_pca20035_common.dts#L164

 

Both are physically connected, but usually only UART0 is active (debug out etc.)

 

Towards integrating the HCI_UART into the nrf9160 side, you have the ble_lte_gateway sample, but on the nRF52840 side, you need to manually combine the hci_uart and the usb_uart bridge (where you disable one of the UARTs, as its going to be used by HCI). Unfortunately, we do not have any example showing exactly this scenario.

 

Kind regards,

Håkon

[dboling]

A question that would save me lots of digging through the code.  Where is the debug output UART defined?  That is, where in the code is it set to UART0 vs UART1 or somewhere else?  Thanks. 

[Håkon Alseth]

Hi,

 

That is defined at the top of the common device tree:

https://github.com/NordicPlayground/fw-nrfconnect-nrf/blob/master/boards/arm/nrf9160_pca20035/nrf9160_pca20035_common.dts#L12

https://github.com/NordicPlayground/fw-nrfconnect-nrf/blob/master/boards/arm/nrf52840_pca20035/nrf52840_pca20035.dts#L15

 

You can override device tree by creating an overlay file, like done here (this one sets the bt-uart interface, but the concept is equal for the console):

https://github.com/NordicPlayground/fw-nrfconnect-nrf/blob/master/samples/nrf9160/lte_ble_gateway/nrf9160_pca10090ns.overlay#L3

The device tree is touched on in this blog post, if you want to know more about it:

https://devzone.nordicsemi.com/nordic/cellular-iot-guides/b/getting-started-cellular/posts/nrf-connect-sdk-tutorial

(here's also part 2 of the ncs tutorial: https://devzone.nordicsemi.com/nordic/cellular-iot-guides/b/getting-started-cellular/posts/nrf-connect-sdk-tutorial---part-2)

 

Kind regards,

Håkon

[dboling]

Thanks for the response. Spent the day trying to combine the USB bridge with the HCI_UART code. I was able to rebuild the original usb-bridge code and make it work. I was even able to spin that code onto a separate thread so that the primary thread could run the HCI_UART code.

First roadblock was finding a spare pin for the needed interrupt. I decided to repurpose the UART0 CTS pin since there's no need to receive any debug data into the 9160. 

I attempted to port the .dts and kconfig files from the 52840_PCA10090 folder to the 52840_PCA20035 board folder. In the end, the reset doesn't seem to be working correctly.

It's sad that this very powerful bluetooth chip on the Thingy doesn't have any better example other than the usb bridge. I know it's early days, but it's a powerful chip and I'd like to take advantage of it. 

Thanks for your help. I'll continue to work with the Thingy codebase.

[Håkon Alseth]

dboling said:

It's sad that this very powerful bluetooth chip on the Thingy doesn't have any better example other than the usb bridge. I know it's early days, but it's a powerful chip and I'd like to take advantage of it. 

 The examples, as of now, is limited, but I will ofcourse give this feedback to the R&D team working on thingy:91.

PS: RTS/CTS can be declared as "0xFFFFFFFF" so that the uart driver interprets them as unused. Flow control isn't enabled between the two nRF's, so they can safely be used.

 

Kind regards,

Håkon