High power consumption after uninit of libuarte

[ilockit_CFR]

Hi,

currently I'm facing an issue with the power consumption of my pcb. The idle power consumption is at about 20 µA. After initialising the UART it goes up to over 1 mA. If I uninitialise the UART again, the power consumption stays at about 280 µA which is much higher than before. At the moment of the test both pins from the UART were disconnected. 

I'm using SDK5 17.1.0 and the following code snippets to (un-)initialise the UART:

//Definition
NRF_LIBUARTE_ASYNC_DEFINE(uart_gsm, 0, 1, NRF_LIBUARTE_PERIPHERAL_NOT_USED, NRF_LIBUARTE_PERIPHERAL_NOT_USED, 255, 3);

// Activation
nrf_libuarte_async_config_t nrf_libuarte_async_config = {
                .tx_pin     = PIN_GSM_RX,
                .rx_pin     = PIN_GSM_TX,
                .baudrate   = NRF_UARTE_BAUDRATE_9600,
                .parity     = NRF_UARTE_PARITY_EXCLUDED,
                .hwfc       = NRF_UARTE_HWFC_DISABLED,
                .timeout_us = 100,
                .int_prio   = APP_IRQ_PRIORITY_LOW_MID
            };

uint32_t err_code = nrf_libuarte_async_init(&uart_gsm, &nrf_libuarte_async_config, uart_gsm_event_handler, (void *)&uart_gsm);
APP_ERROR_CHECK(err_code);

nrf_libuarte_async_enable(&uart_gsm);
            
//Deactivation
nrf_libuarte_async_uninit(&uart_gsm);
           
nrf_gpio_input_disconnect(PIN_GSM_TX);
nrf_gpio_input_disconnect(PIN_GSM_RX);

Is there anything I'm missing when deactivating the UART? How can I go back to my idle power consumption?

Best regards,

Christian 

[Vidar Berg]

Hi Christian,

Based on the pin naming, I assume that you are connected to a GSM modem. Is the current going into the modem part of the measurement, or do you power it off after disabling the UART? 

Best regards,

Vidar 

[ilockit_CFR]

Hi Vidar, 

at the moment the GSM modem is completely disconnected. We observed higher current consumption after using the modem so we investigated where it comes from. We could break it down to the initialisation and uninitialisartion of the UART after we disconnected the whole modem part. So I guessed that there's an issue with the configuration or usage of the UART library, bubt I couldn't find any solution in your examples or the devzone. 

Best regards,

Christian

[Vidar Berg]

Hi Christian,

Thanks for confirming. Is your application requesting the HF crystal oscillator when it enables the UARTE as recommended in the PS? Are there any other pins being used for interfacing with the GSM modem apart from the RX and TX pins? A current draw of 2-300 µA often indicates that there is a floating input or that the crystal oscillator is left running.

Best regards,

Vidar

[ilockit_CFR]

Hi Vidar, 

we only have one other pin to activate/deactivate the modem part, but for the tests this pin is set to LOW the whole time. 

The application does not request the HF oscillator when initialising the UART. How would I do that? I checked it with nrf_drv_clock_hfclk_is_running and it always returned false. 

Best regards,

Christian

[Vidar Berg]

Hi Christian,

You can use the nrf_drv_clock_hfclk_request() function to start up the crystal oscillator, and nrf_drv_clock_hfclk_release() when you no longer need it.

Are you able to share a minimal version of your project so I can try to replicate this issue on a DK? 

Best regards,

Vidar

[ilockit_CFR]

Hi Vidar,

thanks for the hint. I prepared a minimal example. Unfortunately, I have no dev-kit here at the moment, so that I could only test with our custom pcb. I hope it works on your side.  

Best regards,

Christian

[Vidar Berg]

Hi Christian,

Thanks for sharing the project. Unfortunately, I'm currently unable to build Keil projects as I'm running Ubuntu, but I did look at the code and did not spot any errors.

Please try to add the code snippet below after libuarte uninit and see if it makes any difference. This will help confirm if the UARTE peripheral is the culprit or not.

    /* Power-cycle UARTE0 to force release of HF clock request */
    *(volatile uint32_t *)(NRF_UARTE0_BASE + 0xFFC) = 0;
    *(volatile uint32_t *)(NRF_UARTE0_BASE + 0xFFC);
    *(volatile uint32_t *)(NRF_UARTE0_BASE + 0xFFC) = 1;

Best regards,

Vidar

[ilockit_CFR]

Hi Vidar, 

thanks for your support. I tried the code snippet, but nothing changes. So I initialised the UART with two different pins and that led to the correct result. The power consumption was reduced to the expected value after uninit. Obviously, there's an issue with our pcb but that's something I have to discuss with our team. 

Thanks for your time and your help.

Best regards,

Christian