BSP Developer's Guide

VxWorks 5.5
BSP Developer’s Guide
It is recommended that you use CACHE_PIPE_FLUSH between an I/O write
operation and a following I/O read operation. Successive writes or reads should
not require any special protection. It is only when switching from writing to
reading that pipeline flushing becomes essential.
Note that flushing of the write pipeline does not mean the cache is automatically
flushed to memory as well. You must still handle cache issues within the driver.
Conversely, flushing or disabling the cache does not automatically flush or disable
the write pipeline. The write pipeline is first in the hierarchy.
SNOOPED Attribute
This attribute is transparent to all memory types. Portable drivers use the
appropriate flush and invalidate macros. However, if SNOOPED is TRUE, the
macros evaluate to null operations. Target-specific drivers do not need flush or
invalidate macros.
Some systems implement partial snooping. They can read snoop and only
invalidate cache data on a write. This does not meet the requirements for fully
coherent memory. In this case, the SNOOPED attribute is FALSE not TRUE.
MMU_TAGGING Attribute
This attribute is transparent to the memory type obtained using the
cacheDmaMalloc( ) routine. Portable drivers use the CACHE_DMA_FLUSH and
CACHE_DMA_INVALIDATE macros. However, if MMU_TAGGING is TRUE, the
macros evaluate to null operations. Target-specific drivers do not need
CACHE_DMA_FLUSH or CACHE_DMA_INVALIDATE macros.
This attribute does not typically affect memory obtained using the malloc( )
routine, the data section, or the bss section. Therefore, appropriate use of the
CACHE_USER_xxxx and CACHE_DRV_xxxx flush and invalidate macros is
required, as described in Flush and Invalidate Macros, p.107.
USER_DATA_UNKNOWN Attribute
With this attribute, your driver must maintain cache coherency of any data that is
passed directly between the device and the user. For outgoing data, first flush the
user data from the cache with the CACHE_USER_FLUSH macro before
commanding the device to access the data. For incoming data, first invalidate the
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