Thingy:91 nrf9160 to CDC UARTE0_NS comms setup

[Christopher Hunt]

I've got a Thingy:91 plugged into my computer and can see its USB terminals (/dev/tty.usbmodem143101 and /dev/tty.usbmodem143104). I can also see the "ZEPHYR USB" volume and its contents. This indicates to me that the connectivity bridge running on the Thingy:91's nRF52840 is operational.

I'm attempting to write out to UARTE0_NS which has been configured as per the following Zephyr config:

&uart0 {
  compatible = "nordic,nrf-uarte";
  current-speed = <115200>;
  status = "okay";
  tx-pin = <18>;
  rx-pin = <19>;
  rts-pin = <20>;
  cts-pin = <21>;
};

I'm also flashing the SPM sample, which I *think* permits the use of UARTE0_NS.

My program loops on waiting for the transmission to end. Am I missing anything so far?

Thanks.

[Carl Richard]

Hello, Christopher!

The Thingy:91 board files (for the thingy91_nrf52840) shows that UART0 is configured as below. Could you try with that overlay instead and see if it improves?

&uart0 {
	compatible = "nordic,nrf-uarte";
	current-speed = <115200>;
	status = "okay";
	tx-pin = <15>;
	rx-pin = <11>;
	rts-pin = <21>;
	cts-pin = <20>;
};

SPM configures UARTE0 as non-secure, yes.

Best regards,
Carl Richard

[Christopher Hunt]

Thanks, but are you sure? I'm trying to communicate from the nRF9160 to the nRF52840. Your config looks like its from the thingy91_nrf52840.dts file. I'm looking at the thingy91_nrf9160_common.dts. Neither settings are working for me though, but perhaps this is then something else... Any further thoughts?

Also, I just built and flashed the sample connectivity bridge to the Thingy's nRF52840 just to see that all is well there. The volume now mounts as "NONAME", so this confirms that my flashing was correct at least.

[Carl Richard]

Hello again!

Apologies, you are correct. That was from the thingy91_nrf52840.dts file. Your original settings should be correct. What are your flow control settings on the computer side? HW flow control should be disabled by default. 

Best regards,
Carl Richard

[Christopher Hunt]

Thanks for the follow-up and confirming the settings. Setting the flow control explicitly to being software enabled makes no difference for me. I'm not that surprised though as I'd expect software flow control to be used by default given the use of macOS's `screen` command.

[Carl Richard]

Hi again!

Could you try with flow control explicitly disabled? It's disabled by default on the device side, so to see any data on the computer side it must be disabled there as well.

Best regards,
Carl Richard

[Christopher Hunt]

Thanks. Here's the exact command I tried:

screen /dev/tty.usbmodem0009600667481 115200,ixon,ixoff

I understand that the "ixon,ixoff" turns on software flow control. 

[Carl Richard]

Understood. I will try this out on the office mac and see if I can reproduce. In the meantime, could you see if you get different results when using the LTE Link Monitor app from nRF Connect for desktop?

Best regards,
Carl Richard

[Christopher Hunt]

Hmm. I've downloaded the Thingy:91 firmware files again and cannot connect via the LTE Link Monitor app. I installed the client app on the device (serial_lte_modem_2021-03-04_8e8c6089.hex) and ensured that its modem software is up to date.

[Christopher Hunt]

OK, some more info for you. If I completely erase the board and flash the zephyr/samples/basic/blinky_pwm to it, all is well i.e. the LEDs blink and I can connect to the USB serial port and see the PWM debug log messages i.e.

[00:00:24.099,334] <dbg> pwm_nrfx.pwm_nrfx_pin_set: pin 31, pulse 500000, period 1000000, prescaler: 5.

etc.

This categorically proves that the 52840 is forwarding on the UART comms from the 9160. Here's the resultant build/zephyr.dts file for the UART0:

uart0: uart@8000 {
  compatible = "nordic,nrf-uarte";
  reg = < 0x8000 0x1000 >;
  interrupts = < 0x8 0x1 >;
  status = "okay";
  label = "UART_0";
  current-speed = < 0x1c200 >;
  tx-pin = < 0x12 >;
  rx-pin = < 0x13 >;
  rts-pin = < 0x14 >;
  cts-pin = < 0x15 >;
};

There's nothing stated about parity... I assume that it is excluded.

Any more pointers? Thanks.

[Carl Richard]

Hi again, Christopher!

I just tried with the same Serial LTE Modem image and it worked fine. When you say that you cannot connect via the LTE Link Monitor app, is it because you can't see the device or is there no data/messages being transmitted? 

I also successfully connected to the Thingy using "screen" on the Mac. Did you connect to the correct tty.usbmodem device? The Thingy:91 exposes two virtual com ports and only one is for UART logging.

Best regards,
Carl Richard