Shared Memory

Shared memory interfaces are only available with the NuttX kernel build (CONFIG_BUILD_KERNEL=y). These interfaces support user memory regions that can be shared between multiple user processes. The user interfaces are provided in the standard header file include/sys/shm.h>. All logic to support shared memory is implemented within the NuttX kernel with the exception of two low-level functions that are require to configure the platform-specific MMU resources. Those interfaces are described below:

int up_shmat(FAR uintptr_t *pages, unsigned int npages, uintptr_t vaddr)

Attach, i.e, map, on shared memory region to a user virtual address.

Parameters:

• pages – A pointer to the first element in a array of physical address, each corresponding to one page of memory.

• npages – The number of pages in the list of physical pages to be mapped.

• vaddr – The virtual address corresponding to the beginning of the (contiguous) virtual address region.

Returns:

Zero (OK) is returned on success; a negated errno value is returned on failure.

int up_shmdt(uintptr_t vaddr, unsigned int npages)

Detach, i.e, unmap, on shared memory region from a user virtual address.

Parameters:

• vaddr – The virtual address corresponding to the beginning of the (contiguous) virtual address region.

• npages – T The number of pages to be unmapped.

Returns:

Zero (OK) is returned on success; a negated errno value is returned on failure.