System Port

Table 4–30 Wrap Interleave Order (Continued)

PA Bits [5:3] of Transferred QW

Sixth quadword

101

111

001

011

Seventh quadword

110

100

010

000

Eighth quadword

111

101

011

001

 

 

 

 

 

Table 4–31defines the wrap order for double-pumped data transfers.

Table 4–31 Wrap Order for Double-Pumped Data Transfers

PA [5:3] of Transferred QW

First quadword

x00

x01

x10

x11

Second quadword

x00

x01

x10

x11

Third quadword

x01

x00

x11

x10

Fourth quadword

x01

x00

x11

x10

Fifth quadword

x10

x11

x00

x01

Sixth quadword

x10

x11

x00

x01

Seventh quadword

x11

x10

x01

x00

Eighth quadword

x11

x10

x01

x00

 

 

 

 

 

4.7.9 Nonexistent Memory Processing

Like its predecessors, the 21264/EV67 can generate references to nonexistent (NXM) memory or I/O space. However, unlike the earlier Alpha microprocessor implementa- tions, the 21264/EV67 can generate speculative references to memory space. To accom- modate the speculative nature of the 21264/EV67, the system must not generate or lock error registers because of speculative references. The 21264/EV67 translates all mem- ory references through the translation lookaside buffer (TLB) and, in some cases, the 21264/EV67 may generate speculative references (instruction execution down mispre- dicted paths) to NXM space. In these cases, the system sends a SysDc ReadDataError and the 21264/EV67 does the following:

Delivers an all-ones pattern to all load instructions to the NXM address

Force-fails all store instructions to the NXM address (much like a STx_C failure)

Invalidates the cache block at the same index by way of an atomic Evict command

4–38Cache and External Interfaces

Alpha 21264/EV67 Hardware Reference Manual

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Compaq EV67, 21264 specifications Nonexistent Memory Processing, 31defines the wrap order for double-pumped data transfers