Integration notes

This page describes how to integrate the Multiprotocol Service Layer (MPSL) into an application. The descriptions are valid for both RTOS and RTOS-free environments.

For the nRF53 Series, the requirements described are only relevant for applications running alongside the MPSL on the network processor.

The following peripherals are owned by MPSL and must not be accessed directly by the application:

  • RTC0

  • TIMER0

  • TIMER1 (for the nRF53 Series)



  • TEMP

  • PPI channel: 19, 30, 31 (for the nRF52 Series)

  • DPPI channels: 0, 1, 2 (for the nRF53 Series)


These peripherals can be used freely when MPSL is not initialized. Additional peripheral requirements may be set by the protocol stacks in use.

Limited access to these peripherals is provided through the MPSL Timeslot module and other MPSL APIs.

Thread and interrupt safety

The MPSL library is not reentrant. For thread-safe operation, see the <Interrupt configuration>_ and <Scheduling>_ sections below.

Interrupt configuration

MPSL enables interrupts for RTC0, TIMER0, TIMER1 (only on nRF53 Series), POWER_CLOCK, and low_prio_irq. The application must enable and configure all the other interrupts. If the Timeslot API is used for RADIO access, the application is responsible for enabling and disabling the interrupt for RADIO.

The application must configure interrupts for RTC0, TIMER0, and RADIO for priority level 0 ( MPSL_HIGH_IRQ_PRIORITY ). On the nRF53 Series, the application must additionally configure TIMER1 for priority level 0 ( MPSL_HIGH_IRQ_PRIORITY ).

The following interrupts do not have real-time requirements:

  • POWER_CLOCK It is up to the application to forward any clock-related events to MPSL_IRQ_CLOCK_Handler() in lower priority. Irrelevant events are ignored, so the application is free to forward all events for the POWER_CLOCK interrupt.

  • low_prio_irq Low-priority work is signaled by MPSL by adding the IRQ specified in the low_prio_irq argument to mpsl_init(). When this interrupt is triggered, mpsl_low_priority_process() should be called as soon as possible (at least within a couple of ms). The application should configure this interrupt priority lower than MPSL_HIGH_IRQ_PRIORITY level (namely, a higher numerical value). The interrupt is enabled with mpsl_init() and disabled with mpsl_uninit() by MPSL.


The interaction of the MPSL library with protocol stacks is designed to run at two interrupt priority levels: one for the high-priority handlers, and one for the low-priority handler. The interaction of the MPSL library with the application happens in the thread context and in the low-priority handler.

High priority

The high-priority handlers are mostly used for timing-critical operations related to radio or scheduling. Interrupting or delaying these handlers leads to undefined behavior.

Low priority

Low priority is used for background tasks that are not directly tied to the radio or scheduling. These tasks are designed in such a way that they can be interrupted by high-priority code. The tasks are however not designed to be interrupted by other low-priority tasks. Therefore, make sure that only one MPSL API function is called from the application at any time.

  • All protocol stacks using MPSL must be synchronized (namely, not called concurrently) to avoid concurrent calls to MPSL functions.

  • Application must only call MPSL APIs from non-preemptible threads, or with interrupts disabled (namely, during initialization).

  • The mpsl_low_priority_process() function should only be called from thread context, namely, not directly from the software interrupt handler.

  • Alternatively, you can use synchronization primitives to ensure that no MPSL functions are called at the same time.

Other priorities

MPSL initialization functions, like mpsl_init() and mpsl_uninit(), are not thread-safe. Do not call them while, for example, a protocol timeslot is in progress. This must be enforced by application and protocol stacks.

MPSL should be initialized before any protocol stack is enabled, and uninitialized after all protocol stacks have been disabled.

Architecture diagrams

The following image shows how the MPSL integrates into an RTOS-free environment.

MPSL integration in an RTOS-free environment

MPSL integration into an RTOS-free environment

The following image shows how the MPSL integrates into an RTOS.

MPSL integration with an RTOS

MPSL integration into an RTOS