Practical examples

Here's a code snippet that allocates contiguous memory from system RAM:

int fd = posix_typed_mem_open( "/memory/ram/sysram", O_RDWR,
            POSIX_TYPED_MEM_ALLOCATE_CONTIG);

POSIX method:

void *vaddr = mmap( NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);

QNX OS method:

shm_fd = shm_open(SHM_ANON, O_RDWR, 0600);

shm_ctl(shm_fd, SHMCTL_ANON | SHMCTL_TYMEM | SHMCTL_PHYS,
        (uint64_t)tymem_fd, 0x100000);

Assume you have special memory (say fast SRAM) that you want to use for packet memory. This SRAM isn't put in the global system RAM pool. Instead, in startup, we use as_add() (see the Startup Library chapter of Building Embedded Systems) to add an asinfo entry for the packet memory:

as_add(phys_addr, phys_addr + size - 1, AS_ATTR_NONE, "packet_memory", mem_id);

where phys_addr is the physical address of the SRAM, size is the SRAM size, and mem_id is the ID of the parent (typically memory, which is returned by as_default()).

This code creates an asinfo entry for packet_memory, which you can then use as POSIX typed memory. The following code allows different applications to allocate pages from packet_memory:

int fd = posix_typed_mem_open( "packet_memory", O_RDWR,
            POSIX_TYPED_MEM_ALLOCATE);

POSIX method:

void *vaddr = mmap( NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);

QNX OS method:

shm_fd = shm_open(SHM_ANON, O_RDWR, 0600);

shm_ctl( shm_fd, SHMCTL_ANON | SHMCTL_TYMEM, (uint64_t)tymem_fd, 0x100000);

Alternatively, you may want to use the packet memory as direct shared, physical buffers. In this case, applications would use it as follows:

int fd = posix_typed_mem_open( "packet_memory", O_RDWR,
            POSIX_TYPED_MEM_MAP_ALLOCATABLE);

POSIX method:

void *vaddr = mmap( NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, offset);

QNX OS method:

shm_fd = shm_open(SHM_ANON, O_RDWR, 0600);

shm_ctl( shm_fd, SHMCTL_ANON | SHMCTL_TYMEM, (uint64_t)tymem_fd, 0x100000);

In startup, use as_add_containing() (see the Startup Library chapter of Building Embedded Systems) to define an asinfo entry for DMA-safe memory. Make this entry be a child of ram:

as_add_containing( dma_addr, dma_addr + size - 1, AS_ATTR_RAM, "dma", "ram");

where dma_addr is the start of the DMA-safe RAM, and size is the size of the DMA-safe region.

This code creates an asinfo entry for dma, which is a child of ram. Drivers can then use it to allocate DMA-safe buffers:

int fd = posix_typed_mem_open( "ram/dma", O_RDWR,
            POSIX_TYPED_MEM_ALLOCATE_CONTIG);

POSIX method:

void *vaddr = mmap( NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);

QNX OS method:

shm_fd = shm_open(SHM_ANON, O_RDWR, 0600);

shm_ctl(shm_fd, SHMCTL_ANON | SHMCTL_TYMEM | SHMCTL_PHYS,
        (uint64_t)tymem_fd, 0x100000);