RAM 6.0 BUX II Series Betriebsanweisung PDF herunterladen (Seite 14)

VxWorks

Hardware Considerations Guide, 6.0

pciConfigLib, pciConfigShow, pciAutoCfg, and pciIntLib for more information.

Wind River Technical Note #49 also contains information regarding PCI support.

Addressing

The standard Wind River PCI configuration causes all memory space on the PCI

bus to be accessed through the MMU, which requires system memory to hold the

page table entries (PTEs).

Dual-Port Memory

Most CPU boards have local (on-board) RAM on the processor bus. PCI is

normally configured so that all of the on-board RAM is accessible to PCI devices

for data buffers. This is also called dual porting. Dual porting is required for off

board devices that DMA into target memory.

Using processor memory for device data buffers can cause a slight amount of

increased interrupt latency. When the device is transferring data, the processor is

unable to fetch instructions or data required by ISRs immediately due to bus

contention. For most applications, this is not a problem. However, for applications

with extreme low latency requirements, this can be ameliorated somewhat by

locating device buffers in PCI memory

VMEbus

This section discusses issues of concern to the BSP developer considering the

VMEbus.

VME Specification C.1

VME interoperability is crucial for the success of the standard. Special-purpose

extensions to the bus should be confined to the user pins on rows A and C of the

P2, and they should be clearly documented. Under no circumstance is it acceptable

to deviate from the timings presented in the specification.

The VME-64 Specification is a superset of earlier specifications. At this time Wind

River does not provide support for the plug and play features provided in the

VME-64 specification or any of its extensions.

Addressing

The choice of address map is not critical in VxWorks. Local addresses can obscure

parts of the VME bus address space. Some boards cannot address low memory on

the bus because their local address starts at 0. This is not a problem for VxWorks,

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RAM 6.0 BUX II Series Betriebsanweisung Seite 14