Partition manager integration

The Modem library, which runs on the application core, shares an area of RAM memory with the nRF91 Series modem core. During the initialization, the Modem library accepts the boundaries of this area of RAM and configures the communication with the modem core accordingly.

However, it is the responsibility of the application to reserve that RAM during linking, so that this memory area is not used for other purposes and remain dedicated for use by the Modem library.

In nRF Connect SDK, the application can configure the size of the memory area dedicated to the Modem library through the integration layer. The integration layer provides a set of Kconfig options that help the application reserve the required amount of memory for the Modem library by integrating with another nRF Connect SDK component, the Partition Manager.

The RAM area that the Modem library shares with the nRF91 Series modem core is divided into the following four regions:

  • Control

  • RX

  • TX

  • Trace

You can configure the size of the RX, TX and the Trace regions using the following Kconfig options of the integration layer:

The size of the Control region is fixed. The Modem library exports the size value through CONFIG_NRF_MODEM_LIB_SHMEM_CTRL_SIZE. This value is automatically passed by the integration layer to the library during the initialization through nrf_modem_lib_init().

When the application is built using CMake, the Partition Manager automatically reads the Kconfig options of the integration layer. Partition manager decides about the placement of the regions in RAM and reserves memory according to the given size. As a result, the Partition manager generates the following definitions:

  • PM_NRF_MODEM_LIB_CTRL_ADDRESS - Address of the Control region

  • PM_NRF_MODEM_LIB_TX_ADDRESS - Address of the TX region

  • PM_NRF_MODEM_LIB_RX_ADDRESS - Address of the RX region

  • PM_NRF_MODEM_LIB_TRACE_ADDRESS - Address of the Trace region

  • PM_NRF_MODEM_LIB_CTRL_SIZE - Size of the Control region

  • PM_NRF_MODEM_LIB_TX_SIZE - Size of the TX region

  • PM_NRF_MODEM_LIB_RX_SIZE - Size of the RX region

  • PM_NRF_MODEM_LIB_TRACE_SIZE - Size of the Trace region

These definitions will have identical values as the CONFIG_NRF_MODEM_LIB_SHMEM_*_SIZE configuration options.


The heap implementation used for allocations on the TX region has an overhead of up to 128 bytes. Adjust the size of the TX region accordingly, so that its size is 128 bytes larger than the largest allocation you expect to happen (longest AT command, largest payload passed to nrf_send()) in your application.

When the Modem library is initialized by the integration layer in nRF Connect SDK, the integration layer automatically passes the boundaries of each shared memory region to the Modem library during the nrf_modem_lib_init() call.