nRF54L15 bare-metal BLE disables UART RX

[strz]

Hello,

We're using nrf-sdk-bm v0.9.0 and having an issue with BLE and UART coexistence. The goal is to be able to operate in and transition between three modes: UART alone, UART/BLE together, and BLE alone.

We are able to connect over UART at 921600 baud and send/receive. When we start BLE advertising, the UART continues to send logs but doesn't respond to commands until the device is rebooted.

The working hypothesis is that UART receive requires the Constant Latency sub-power mode, but the SoftDevice overrides this to Low-power (either when starting advertising or earlier when enabled). 

I've been experimenting to try and recover the UART by requesting Constant Latency mode again, but this doesn't seem to be very reliable.

void RequestConstantLatency()
{
    // If the SoftDevice is enabled use the SVC call.
    if (nrf_sdh_is_enabled())
    {
        uint32_t ret = sd_power_mode_set(NRF_POWER_MODE_CONSTLAT);
        if (ret == NRF_SUCCESS)
        {
            LOG_INFO("Constant latency mode requested (SD)");
        }
        else
        {
            LOG_ERROR("Failed to request constant latency mode (SD): %u", ret);
        }
    } else {
        nrfx_err_t err = nrfx_power_constlat_mode_request();
        if (err == NRFX_SUCCESS)
        {
            LOG_INFO("Constant latency mode requested (nrfx)");
        }
        else
        {
            LOG_ERROR("Failed to request constant latency mode (nrfx): %u", err);
        }
    }
}

Is there any documentation on when the SoftDevice requests Low-Power mode, or guidance on how to use both interfaces at the same time?

We're using UARTE21, and the board has UART_RX into P2.07/SWO and UART_TX into P2.08

[Turbo J]

You are using pins across power domains. Either use UART00 or use pins from Port 1. 

See Figure 1 in Product overview (datasheet), which shows power domains for peripherials and GPIO ports.

[Yanqil]

Hi, thank you for the reply.  Switching to UART00 seems to have resolved the issue.  Some follow up questions: 

- We used Table 73 in the datasheet to help us pick the peripherals and the table indicated that UARTE 21 is valid for P2 pins 7 and 8.  Can you point us to where in the datasheet we can find information that we are crossing power domains by using UART21 on port 2 pins?  This way, we can check if there are other irregularities.

- Is there a tool that we can use to help check pin to peripheral mapping?  Other vendors I've used in the past has GUI tools that help generate configuration files.