RE: nRF52832 + NCS v3.3.1 + MPSL: UARTE disable/enable at runtime breaks BLE connection

Nordfield — Sat, 11 Jul 2026 03:43:14 GMT

Platform:

Chip: nRF52832 (QFAA)
SDK: nRF Connect SDK (NCS) v3.3.1 based on Zephyr RTOS
SoftDevice: S140 (integrated in Zephyr build, MPSL enabled)
Toolchain: nRF Connect for Desktop

Application Overview:
We are developing a BLE UART transparent transmission module (NUS service). The module works as a BLE Peripheral, receiving AT commands and data from a host device via BLE, and forwarding them to a target device via UART, and vice versa.

UART Working Mode:

UART baudrate: configurable from 4800 to 921600 via AT commands (runtime changeable)
UART pins: TX=P0.06, RX=P0.08
When UART is actively transmitting/receiving data, it operates normally in interrupt-driven mode
When UART is idle for a configurable timeout (default 3 minutes), the module should enter low-power sleep mode:
- UART peripheral should be fully powered down / disabled to minimize leakage current
- RX pin is configured as GPIO wake source (edge-triggered interrupt) to detect incoming data and wake the module
When data arrives on RX pin during sleep:
- GPIO interrupt triggers
- UART peripheral is re-enabled and re-initialized
- Normal UART communication resumes
Power Consumption Requirement:
Target idle current: as close to the nRF52832 base current as possible (~0.3mA or less)
The old firmware (nRF5 SDK 17.0 + SoftDevice S132, no MPSL) achieves this by calling app_uart_close() → nrf_drv_uart_uninit() → nrf_uarte_disable() to fully power down the UARTE peripheral during sleep, and uart_init() to fully re-initialize on wake. This works perfectly with no BLE issues.

The Problem:
In the NCS/Zephyr + MPSL architecture, any direct UARTE register operations (including nrf_uarte_disable(), nrf_uarte_int_disable(), STOPRX/STOPTX tasks) conflict with MPSL shared resources and cause BLE connection failures. Even the Zephyr UART Async API (uart_rx_disable() / uart_rx_enable()) causes BLE connection failures on nRF52832.

What We Need:
A recommended approach to fully power down the UARTE peripheral during idle periods on nRF52832 with NCS/Zephyr + MPSL, and re-enable it on GPIO wake, without breaking BLE connectivity. Specifically:

Is there a safe API or driver-level method to completely disable UARTE (similar to nrf_drv_uart_uninit() in nRF5 SDK) that is compatible with MPSL?
If direct register access is not safe, what is the correct Zephyr driver approach to power down UART when idle and restore it on wake?
Are there any known limitations or workarounds for UART Async API coexistence with BLE on nRF52832?

Additional Note:

CONFIG_PM is not available on nRF52832 (Zephyr power management framework not supported for this SoC)
LFCLK source: internal RC oscillator (no external 32.768kHz crystal)
P0.09 and P0.10 are used as GPIO (LED and BUTTON), requiring UICR.NFCPINS to be configured for GPIO mode