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  • Case ID: 346276
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nrf5340 current consumption of shell by using uart async api

whati001

Hi Nordic Team,

am I currently evaluating the nrf5340 development kit for our new product revision and fail to get a power efficient shell besides rtt logigng.

Concrete, I am trying to achieve the following:

* Debug Logging via RTT

* Shell access via UART (async API)

As a base, I have used the blinky example and added the following KConfig options to my prj.conf:


CONFIG_GPIO=y

# enable logging via segger RTT
CONFIG_LOG=y
CONFIG_LOG_PRINTK=y
CONFIG_USE_SEGGER_RTT=y
CONFIG_LOG_BACKEND_RTT=y

# uart
CONFIG_SERIAL=y
CONFIG_UART_ASYNC_API=y

# enable shell
CONFIG_SHELL=y
CONFIG_SHELL_ASYNC_API=y
CONFIG_SHELL_BACKEND_SERIAL=y
CONFIG_SHELL_BACKEND_SERIAL_API_ASYNC=y
CONFIG_SHELL_BACKEND_SERIAL_INTERRUPT_DRIVEN=n
CONFIG_SHELL_LOG_BACKEND=n

# CONFIG_PM=y
CONFIG_PM_DEVICE=y

The application works fine, but the current consumption in IDLE mode is not fine. I receive the logs via RTT and can connect to the UART shell.

The PPK2, in ampere mode, shows an average current of ~650uA, which is the UART peripheral.

If I disbale the SHELL (CONFIG_SHELL=n), the current drops to around ~3uA to 5uA, which is what I am targetting for. The current consumption is also fine, if I print log via the UART. But after enabling the CONFIG_SHELL option, it seems like that the UART never goes into IDLE mode. But I have enabled all possible ASYNC_API options I have found in the source code.

What I would expect is that the current remains at ~3uA to 5uA if no UART communication is going one.

Maybe you can help me to find the proper KConfig parameters to reduce the current consumption of the shell.

---

Update from my side: After some more reserach I think this current consumption is normal and caused by the active UART RX. My should already use the ASNY API of the UART.

So let me change this/add a new question. Is it possible to reduce the UART RX current somehow? I am thinking about:

* hardware control CTS/RTS lines (CONFIG_UART_LINE_CTRL=y) has not reduce the current for me

* wake on character (guess the nrf5340 does not support this)  

Best regards

Andreas Karner

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    Hi Andreas,

    The UART continues to request the HF clock source as long as rx reception is enabled, which results in the increased idle current you measured. The standard HW control signals are not asserted early enough for the HF clock to start up and for the UART to resume receiving data in time. But if you control the UART driver implementation on both sides, you may consider using our Low power UART driver with the custom handshake signals.

    Best regards,

    Vidar

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  • 0

    Hi Andreas,

    The UART continues to request the HF clock source as long as rx reception is enabled, which results in the increased idle current you measured. The standard HW control signals are not asserted early enough for the HF clock to start up and for the UART to resume receiving data in time. But if you control the UART driver implementation on both sides, you may consider using our Low power UART driver with the custom handshake signals.

    Best regards,

    Vidar

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