2

Raven PCI Bridge ASIC

MPC Bus Address Space

The Raven will map MPC address space into PCI Memory space using four programmable map decoders. The most significant 16 bits of the PCI address are compared with the address range of each map decoder; if the address falls within the specified range, the access is passed on to the MPC bus. An example of this appears in Figure 2-4.

PCI Bus Address

8

0

 

 

 

 

8 0

 

 

1

2 3 4

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

31

 

 

 

 

 

 

 

 

16

 

15

0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Decode is

 

 

 

 

and

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

>=

 

 

<=

 

 

PSADDx Register

7

 

0

 

8

 

0

 

9

 

0

 

0

 

0

 

 

 

 

 

 

 

 

 

 

 

31

16

15

0

Figure 2-4. PCI to MPC Address Decoding

The Raven ASIC imposes no limits on how large an address space a map decoder can represent. There is a minimum of 64KB due to the resolution of the address compare logic.

For each map, there is an associated set of attributes. These attributes are used to enable read accesses, enable write accesses, enable write-posting, and define the MPC bus transfer characteristics.

Each map decoder also includes a programmable 16-bit address offset. The offset is added to the 16 most significant bits of the PCI address, and the result is used as the MPC address. This offset allows devices to reside at any MPC address, independent of the PCI address map. An example of this appears in Figure 2-5.

2-12

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Image 82
Motorola MVME2300 Series manual MPC Bus Address Space, PCI to MPC Address Decoding