The memory map for program memory and RAM when the SoftDevice is enabled is described in this section.
Figure 1 illustrates the memory usage of the SoftDevice alongside an user application. The flash memory for the SoftDevice is always reserved and the application program code should be placed above the SoftDevice at APP_CODE_BASE. The SoftDevice uses the first 8 bytes of RAM when not enabled. Once enabled, the RAM usage of the SoftDevice increases: the RAM requirements of an enabled SoftDevice are detailed in Table 2. With the exception of the call stack, the RAM usage for the SoftDevice is always isolated from the application usage; thus the application is required to not access the RAM region below APP_RAM_BASE. The value of APP_RAM_BASE is obtained by calling sd_softdevice_enable, which will always return the required minimum start address of the application RAM region for the given configuration. An access below the required minimum application RAM start address will result in undefined behavior, see Table 2 for minimum RAM requirements.