CACHE_FLUSH()

Flush cache lines associated with a data buffer

Synopsis:

#include <sys/cache.h>

CACHE_FLUSH(struct cache_ctrl *cinfo, 
            void *vaddr, 
            uint64_t paddr, 
            size_t len);

Arguments:

cinfo: A pointer to the structure that was initially passed to cache_init().
vaddr: The virtual address of the buffer; this is a pointer to the data in the driver's virtual address space.
paddr: The physical address of the buffer: this is typically in the same address space that the external device will use to reference the data. The physical address is obtained by calling mem_offset64(). Since this function is fairly costly, drivers typically allocate a pool of data buffers at initialization (e.g., by calling mmap() with the MAP_SHARED | MAP_PHYS | MAP_ANON flags), and predetermine the physical addresses of the data.
len: The number of bytes in the buffer, for which cached data should be flushed to memory.

Library:

libcache

Use the -l cache option to qcc to link against this library.

Description:

This macro is used to flush any cache lines associated with a data buffer out to memory. This routine ensures that any modifications that have been made to the data by the CPU will be reflected by the contents of memory, and thus an external device reading the data won't retrieve stale data. For more information about cache coherency, see the entry for cache_init().

Note: This macro was added in QNX Momentics 6.3.0 SP2.

Depending on the architecture and the cache callouts (see “Cache control” in the “Kernel Callouts” chapter of Building Embedded Systems), the calling thread might need to obtain I/O privileges before using the CACHE_*() macros. If so, then:

The process must have the PROCMGR_AID_IO ability enabled. For more information, see procmgr_ability().
The thread must call ThreadCtl(), specifying the _NTO_TCTL_IO flag:
```
ThreadCtl( _NTO_TCTL_IO, 0 );
```

Failing to do so may result in a SIGILL (illegal instruction) signal.

Environment variables:

The following environment variables, if they exist, affect the behavior of this function:

CACHE_NOP: Instructs the library that the CACHE_FLUSH() and CACHE_INVAL() macros should have no effect.
CACHE_MSYNC: Instructs the library that the CACHE_FLUSH() and CACHE_INVAL() macros should use the msync() C library call to perform cache synchronization.

Classification:

QNX Neutrino

Safety:
Cancellation point	No
Interrupt handler	Yes
Signal handler	Yes
Thread	Yes

Caveats:

CACHE_FLUSH() is implemented as a macro.