Possible to fully turn off UART from Zephyr based application?

RE: Possible to fully turn off UART from Zephyr based application?

Didrik Rokhaug — Tue, 15 Mar 2022 13:42:02 GMT

After connecting to the debugger with JLinkExe in one terminal, you can get the log in another terminal by running JLinkRTTClient.

See the last step (3): https://infocenter.nordicsemi.com/topic/ug_gsg_ses/UG/gsg/connect_rtt_linux.html

RE: Possible to fully turn off UART from Zephyr based application?

tedhavelka — Fri, 11 Mar 2022 19:16:48 GMT

Hello Didrik,

Thank you for the sample app. I've just compiled and flashed your shared, modified hello_world app onto our board. I've invoked `JLinkExe -if SWD` and connected to our ARM Cortex-M33 application processor, as I did in the post a day or two ago. Same behavior. I can connect, but I do not see any messages over RTT. Also no error messages from JLinkExe itself.

Is there a JLinkExe command I must issue to start the presentation of messages coming across the RTT based physical link?

JLinkExe has several dozen commands, but none jumps out as a 'start logging / start dispaly' type command. These commands largely look like commands I would find in the debugger `gdb`.

- Ted

RE: Possible to fully turn off UART from Zephyr based application?

Didrik Rokhaug — Fri, 11 Mar 2022 14:50:21 GMT

Are you sure your application is outputting any logs?

I've attached a slightly modified version of the hello_world sample, which prints using both log and printk, and can be configured to print over both UART and RTT.

In the current state, it will only print over RTT, but if you comment out/enable the configs that are currently disabling UART, you will get log over UART as well.

Could you try it, to see if you are able to get RTT log with a known good application?

devzone.nordicsemi.com/.../2744.hello_5F00_world.zip

RE: Possible to fully turn off UART from Zephyr based application?

tedhavelka — Wed, 09 Mar 2022 22:24:29 GMT

Hello Didrik,

Thank you for the further instructions on Kconfig symbol settings for Segger based RTT console. I'd actually found a number of posts on this very topic last night ( Devzone 75533, Devzone 46083, Devzone 81416 ). So far I have tried applying these three config symbols (and a few others from the three posts above, and a Nordic pelion sample app Kconfig file) but am not seeing any messages over RTT. Here is a command line excerpt which shows invocation of JLinkExe and connection to an ARM Cortex-M33, the application processor in our board's nRF9160 SiP:

```ted@localhost:~$ JLinkExe -if SWD
SEGGER J-Link Commander V7.60g (Compiled Feb 2 2022 10:33:39)
DLL version V7.60g, compiled Feb 2 2022 10:33:24

Connecting to J-Link via USB...O.K.
Firmware: J-Link V11 compiled Dec 9 2021 14:14:49
Hardware version: V11.00
S/N: 51018155
License(s): GDB
USB speed mode: High speed (480 MBit/s)
VTref=1.859V

Type "connect" to establish a target connection, '?' for help
J-Link>connect
Please specify device / core. <Default>: CORTEX-M33
Type '?' for selection dialog
Device>?
_IceTransOpen: Unable to Parse address lightdm
Qt: Session management error: Could not open network socket
Specify target interface speed [kHz]. <Default>: 4000 kHz
Speed>

Device "CORTEX-M33" selected.

Connecting to target via SWD
Found SW-DP with ID 0x6BA02477
DPIDR: 0x6BA02477
CoreSight SoC-400 or earlier
Scanning AP map to find all available APs
AP[7]: Stopped AP scan as end of AP map has been reached
AP[0]: AHB-AP (IDR: 0x84770001)
AP[1]: AHB-AP (IDR: 0x24770011)
AP[2]: JTAG-AP (IDR: 0x12880000)
AP[3]: APB-AP (IDR: 0x54770002)
AP[4]: JTAG-AP (IDR: 0x12880000)
AP[5]: JTAG-AP (IDR: 0x12880000)
AP[6]: MEM-AP (IDR: 0x128800A1)
Iterating through AP map to find AHB-AP to use
AP[0]: Core found
AP[0]: AHB-AP ROM base: 0xE00FF000
CPUID register: 0x410FD212. Implementer code: 0x41 (ARM)
Feature set: Mainline
Found Cortex-M33 r0p2, Little endian.
FPUnit: 8 code (BP) slots and 0 literal slots
Security extension: implemented
Secure debug: enabled
CoreSight components:
ROMTbl[0] @ E00FF000
[0][0]: E000E000 CID B105900D PID 000BBD21 DEVARCH 47702A04 DEVTYPE 00 Cortex-M33
[0][1]: E0001000 CID B105900D PID 000BBD21 DEVARCH 47701A02 DEVTYPE 00 DWT
[0][2]: E0002000 CID B105900D PID 000BBD21 DEVARCH 47701A03 DEVTYPE 00 FPB
[0][3]: E0000000 CID B105900D PID 000BBD21 DEVARCH 47701A01 DEVTYPE 43 ITM
[0][5]: E0041000 CID B105900D PID 002BBD21 DEVARCH 47724A13 DEVTYPE 13 ETM
[0][6]: E0042000 CID B105900D PID 000BBD21 DEVARCH 47701A14 DEVTYPE 14 CSS600-CTI
Cortex-M33 identified.
J-Link>

```

I've also tried the GUI version `JLinkRTTViewerExe`. Successful target processor connection there too, but no messages from my application firmware.

Early on JLinkExe reports a VTref of about 1p8 volts. Could this voltage be too low to support RTT communications via a JLink Base, hardware version 11.0?

Are there any other Kconfig symbols I could check in menuconfig? That is, by invoking `west build -t menuconfig` in my Zephyr app top directory? Could some other project setting be overriding the three symbols you shared in your latest reply?

- Ted

RE: Possible to fully turn off UART from Zephyr based application?

Didrik Rokhaug — Wed, 09 Mar 2022 12:37:04 GMT

[quote user="tedhavelka"]I'm searching for examples now but you may be able to speed me there sooner: is the API macro or function I need to send messages to RTT console `NRF_LOG()`? This question I make in the context of Nordic ncs 1.6.1 and a Zephyr based application.[/quote]

NRF_LOG was used in the nRF5 SDK.

In NCS, the corresponding macro is LOG_<level>, where <level> is one of DBG, INF, WRN, ERR.

printf() or printk() can also be used.

However, to get the output over RTT, you must enable the RTT backend:

# Enable RTT
CONFIG_USE_SEGGER_RTT=y

# Send log over RTT
CONFIG_LOG_BACKEND_RTT=y
#(Optionally also CONFIG_LOG_BACKEND_UART=n, you'll probably get some Kconfig warnings without)

# Send printk/printf over RTT
CONFIG_RTT_CONSOLE=y
#(Optionally also CONFIG_UART_CONSOLE=n)

RE: Possible to fully turn off UART from Zephyr based application?

tedhavelka — Wed, 09 Mar 2022 00:45:51 GMT

Hello Didrik,

Thank you for the link to command line JLinkExe utility. It turns out I have that installed, it's alongside `nrfjprog` which I use at the command line. I just had not occasion yet to review all the utilities which install with Segger JLink drivers for Linux.

I'm searching for examples now but you may be able to speed me there sooner: is the API macro or function I need to send messages to RTT console `NRF_LOG()`? This question I make in the context of Nordic ncs 1.6.1 and a Zephyr based application.

- Ted

RE: Possible to fully turn off UART from Zephyr based application?

Didrik Rokhaug — Mon, 07 Mar 2022 15:52:58 GMT

[quote user="tedhavelka"]By the way I think that a hyperlink to the blog post you mention at end of your message might be missing. I don't know which blog to which you refer, and cannot review that.[/quote]

Yes, sorry. Here is the link: https://devzone.nordicsemi.com/guides/cellular-iot-guides/b/hardware-design/posts/getting-started-with-current-measurements-on-the-nrf9160?CommentId=b6127988-c126-4d90-a566-86596e84a0f0

I've also edited my previous reply to include the link.

[quote user="tedhavelka"]To confirm then, I may keep CONFIG_SERIAL=y, and on demand suspend one or more on-chip UARTs by calling pm_device_state_set(zephyr_device_handle, <new state>, NULL, NULL), and enjoy the lowest nRF9160 power consumption as if I had disabled all UARTs at compile time?[/quote]

Yes. That should disable UART RX, which is what uses the HF clock and consumes power.

[quote user="tedhavelka"](4) Regarding RTT logging, this is less accessible to me as I am building and developing at the command line on Linux, and have Segger installed in only one of the places I get to work. But I'm noting this UART based alternative for debugging. Thank you for educating me[/quote]

You don't need the full Segger Embedded Studio IDE to read RTT.

J-Link RTT Viewer works on Linux, or you can use the command line: https://infocenter.nordicsemi.com/topic/ug_gsg_ses/UG/gsg/connect_rtt_linux.html

RE: Possible to fully turn off UART from Zephyr based application?

tedhavelka — Fri, 04 Mar 2022 21:07:35 GMT

Hello Didrik,

To your questions:

(1) I am using ncs v1.6.1

(2) In app space periodic accelerometer readings stop working. This sensor is I2C based, and so depends on the high speed clock for operation with the app firmware.

(3) There is a thread I can use to flash an LED on the board, it is a custom and optional thread I'm using for new feature development. That should only depend upon gpio type devices, not high speed clocks.

(4) Regarding RTT logging, this is less accessible to me as I am building and developing at the command line on Linux, and have Segger installed in only one of the places I get to work. But I'm noting this UART based alternative for debugging. Thank you for educating me!

I am working presently to implement a couple of tests and confirm or disconfirm the seeming "dead in the water" nature of my app when CONFIG_SERIAL=n in the app's prj.conf file. I'll update you on my findings in this regard, soon as possible.

Thank you also for explaining the use of `child_image` directory and amending files added there, per your example `child_image/mcuboot.conf`. These conf files sound akin to the manner in which device tree language supports additive and change-wise amendments in dot overlay files. That will be helpful to keep such configuration changes in application space, where they can be git tracked.

By the way I think that a hyperlink to the blog post you mention at end of your message might be missing. I don't know which blog to which you refer, and cannot review that.

To confirm then, I may keep CONFIG_SERIAL=y, and on demand suspend one or more on-chip UARTs by calling pm_device_state_set(zephyr_device_handle, <new state>, NULL, NULL), and enjoy the lowest nRF9160 power consumption as if I had disabled all UARTs at compile time?

- Ted

RE: Possible to fully turn off UART from Zephyr based application?

Didrik Rokhaug — Fri, 04 Mar 2022 13:38:10 GMT

Hi,

Just to be sure, what NCS version are you currently using?

[quote user=""]One post mentions that `mcuboot` and `spm` firmware modules must also be assured to have their prj.conf files disable serial port use and logging. But I am having trouble locating the prj.conf file for Nordic's ncs/nrf/modules/mcuboot application. There's no instance of CONFIG_SERIAL in this sub-project or application element of the larger SDK. Am I correct here that there is not logging and not serial port use in mcuboot?[/quote]

MCUBoot does have logging enabled by default.

The easiest way to configure child images, rather than chasing down their prj.conf files, is to add a folder called "child_image" in your project folder, and inside there a file called <child_image>.conf. I.e. for MCUBoot, you would have <your project folder>/child_image/mcuboot.conf.

[quote user=""]I find that other parts of current firmware app stop working with this sole change CONFIG_SERIAL=y to CONFIG_SERIAL=n. This does not make sense to me.[/quote]

This sounds strange to me as well. What parts of the application stops working?

Do you have any way of getting information from the device other than serial that can give us some insight into what is happening?

What if you log over RTT instead of UART? Does your application work then?

[quote user=""]Last question I have, not answered by these more recent posts, can a run time UART setting to state PM_DEVICE_STATE_SUSPENDED permit the nRF9160 to draw its ultimately lowest spec'd current of about 1.4uA?[/quote]

Yes, that should disable the UART, so that the UART does not consume any power.

You might also be interrested in the low_power_uart driver, which adds two extra GPIO pins (replacing the normal HW flow control pins), which are used to control when the UART has RX enabled (which is what requires power).

Finally, just to be sure, could you try to meassure the current consumption with the application found in this blog post? That way we can verify that the problem is the application, and not something else in your meassurement setup.

Best regards,

Didrik