BSP Developer's Guide

VxWorks 5.5
BSP Developer’s Guide
Device drivers are one of the module types in a VxWorks system that can have
problems with data cache coherency. (Note that the CPU instruction cache
coherency is maintained elsewhere in the system.) This document describes the
issues of concern to the driver writer and describes how to use the cacheLib to deal
with these issues.
This document also describes how to enable the virtual memory library. This is
necessary if you are using 68K or SPARC architectures. In these architectures, the
VxWorks cache library controls the cache by calling the virtual memory library to
manipulate the memory management unit (MMU).
Only drivers using direct memory access (DMA) need to be concerned with cache
issues. It is only in the area of DMA that caching is a consideration for a device
driver. On architectures that do write-buffering, the driver needs to consider issues
related to WRITE_PIPING.
NOTE: If your target architecture includes an MMU, and you disable virtual
memory support but enable the data cache, then cacheDmaMalloc( ) is unable to
provide buffers safe from cache coherency issues.
NOTE: If you use an MMU, the cache modes are controlled by the cache mode
values in the sysPhysMemDesc[ ] table and not by the configuration macros
USER_I_CACHE_MODE and USER_D_CACHE_MODE. It is a common mistake to
assume these macros always control the cache operating mode.
5.7 Helpful Hints
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Avoiding printf( ) in drivers
Avoid use of printf( ) in drivers, even for debugging purposes. Use logMsg( )
instead. There may be system interactions between the driver and the I/O
system that would cause printf( ) to crash the system.
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Calling intConnect( )
Do not call intConnect( )—or any other routine that calls malloc( )—from
within sysHwInit( ). The memory partition library is not initialized and the
system crashes.
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