Low power mode with nrf9160 and cat_tracker application

RE: Low power mode with nrf9160 and cat_tracker application

Tjaz — Mon, 16 Mar 2020 08:52:54 GMT

Hi,

we managed to figure it out. Setting only TASKS_STOPTX and TASKS_STOPRX does not turn UART off fully.
If it helps anyone else, the following two functions do all we need to fully disable and enable UART 0, as well as prevent leaking of current out of the pins.

void uart_0_disable(void)
{
    // stop tx and rx
    NRF_UARTE0->TASKS_STOPTX = 1;
    NRF_UARTE0->TASKS_STOPRX = 1;
    // disable whole UART 0 interface
    NRF_UARTE0->ENABLE = 0;

    // deselect rx and tx pins and clear them
    NRF_UARTE0->PSEL.TXD = 0xFFFFFFFF;
    NRF_P0_NS->OUTCLR = (1 << UART0_TX_PIN);

    NRF_UARTE0->PSEL.RXD = 0xFFFFFFFF;
    NRF_P0_NS->OUTCLR = (1 << UART0_RX_PIN);

    // reconfigure them as GPIO pins and set them to output/0
    gpio_pin_configure(gpio_dev, UART0_RX_PIN, GPIO_DIR_OUT);
    gpio_pin_write(gpio_dev, UART0_RX_PIN, 0);

    gpio_pin_configure(gpio_dev, UART0_TX_PIN, GPIO_DIR_OUT);
    gpio_pin_write(gpio_dev, UART0_TX_PIN, 0);
}

void uart_0_enable(void)
{
    // select pins
    NRF_UARTE0->PSEL.TXD = UART0_TX_PIN;
    NRF_UARTE0->PSEL.RXD = UART0_RX_PIN;

    // enable interface
    NRF_UARTE0->ENABLE = 8;
    NRF_UARTE0->TASKS_STARTRX = 1;
    NRF_UARTE0->TASKS_STARTTX = 1;
}

The same can be done for other UARTs, just replace NRF_UARTE0 with NRF_UARTE1, for example.

It would be immensely helpful, if things like this were documented, instead of having to scour devzone, trying and merging different answers.

Regards,
Tjaž V

RE: Low power mode with nrf9160 and cat_tracker application

Martin Lesund — Tue, 25 Feb 2020 14:16:09 GMT

Hi Tjaz,
No, I am not suggesting that at all.

If you have called the function lte_lc_offline(), the modem goes to offline mode.
Try to call the function lte_lc_power_off(), to put the modem in Power OFF mode and see if that changes the power consumption.

I am not too familiar with the cat tracker application since it is not in the official NCS repository, but let me try to come with some suggestions.

If you check the .config file in the build/zephyr folder you can check which peripherals and modules that are enabled in the application.

To check e.g. peripherals in runtime you could either read directly the registers or utilize the driver APIs if they support that function.
Please check out this pull request of the Serial LTE modem example on how it goes to sleep mode and turn OFF the UART in runtime.

RE: Low power mode with nrf9160 and cat_tracker application

Tjaz — Thu, 20 Feb 2020 08:36:22 GMT

Hi,

we are not actually using PSM - i.e. we do not request it from the network with lte_lc_psm_req.
We connect with lte_lc_init_and_connect(), send our data and then disconnect with lte_lc_offline();

So you are suggesting that not using PSM mode, the modem and/or SIM card is still communicating with the network and thus using power?

Best Regards,
Tjaž V

RE: Low power mode with nrf9160 and cat_tracker application

Martin Lesund — Mon, 17 Feb 2020 13:42:54 GMT

Hi Tjaz,
Before digging into your code, please state which SIM card you are using?
And also which network you are connecting to can be interesting.

I would like you to try to increase the PSM interval (RPTAU) to over 10 minutes to see if there is a restriction in the SIM card.

Some SIM cards require that the modem needs to stay in PSM mode longer than 10 minutes so the SIM card can go in Shut down mode and draw around (~0,01µA).

I may suspect that this could be the idle current from the SIM card.

Best regards,
martin L,