Motorola MVME2400 Series Manuel de service télécharger pdf (Page 88)

2-30 Computer Group Literature Center Web Site

Hawk PCI Host Bridge & Multi-Processor Interrupt Controller

The PHB performs contiguous I/O addressing when the MEM bit is clear

and the IOM bit is clear. The PHB takes the PPC address, apply the offset

specified in the XSOFFx register, and map the result directly to PCI.

The PHB performs spread I/O addressing when the MEM bit is clear and

the IOM bit is set. The PHB takes the PPC address, applies the offset

specified in the MSOFFx register, and maps the result to PCI as shown in

Figure 2-6.

Figure 2-6. PCI Spread I/O Address Translation

Spread I/O addressing allows each PCI device’s I/O registers to reside on

a different PPC memory page, so device drivers can be protected from

each other using memory page protection.

All I/O accesses must be performed within natural word boundaries. Any

I/O access that is not contained within a natural word boundary results in

unpredictable operation. For example, an I/O transfer of four bytes starting

at address $80000010 is considered a valid transfer. An I/O transfer of four

bytes starting at address $80000011 is considered an invalid transfer since

it crosses the natural word boundary at address $80000013/$80000014.

1915 9702

PPC Address + Offset

31 12 11 5 4 0

31 0

PCI Address

25 24

0 0 0 0 0 0 0

0000000

1 2 ... 83 84 85 86 87 88 89 90 91 92 93 ... 353 354

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Motorola MVME2400 Series Manuel de service Page 88