Compaq EV67 Manual De Usuario

Cache and External Interfaces

point is the QW  pointed to by the 21264/EV67; however, some systems may find it 
more beneficial to begin the transfer elsewhere. The system must always indicate the 
starting point to the 21264/EV67. The wrap order for subsequent QWs is interleaved.

Table 4–29 defines the method for systems to specify wrap and deliver data.

Transfers to and from the 21264/EV67 have eight data cycles for a total of 
eight quadwords. The starting point is defined by the system. The preferred 
starting point is the one pointed to by SysAddOut_L[5:4]. Systems can 
insert the SysAddOut_L[5:4] into the SysDc[1:0] field of the command. 
See Table 4–30 for the wrap order.

LW and byte/word read transfers differ from all other transfers. The system 
unloads only four QWs of data into eight data cycles by sending each QW 
twice (referred to as double-pumped data transfer). The first QW returned 
is determined by SysAddOut_L[4:3]. The system again may elect to 
choose its own starting point for the transfer and insert that value into 
SysDc[1:0]. See Table 4–31 for the wrap order.

Table 4–30 defines the interleaved scheme for the wrap order.

Memory

100 (ReadData)

Block (64 Bytes)

See Note 1

Memory 101(ReadDataDirty)

Block (64 Bytes)

See Note 1

Memory 110 

(ReadDataShared)

Block (64 Bytes)

See Note 1

Memory

111(Read DataShared/Dirty)

Block (64 Bytes)

See Note 1

Memory

010 (WriteData)

Block (64 Bytes)

See Note 1

I/O

100 (ReadData)

QW (8-64 Bytes)

See Note 1

I/O

100 (ReadData)

LW(4-32 Bytes)

See Note 2

I/O

100 (ReadData)

Byte/Word

See Note 2

I/O

010 (WriteData)

QW (8-64 Bytes)

See Note 1

I/O

010 (WriteData)

LW(4-32 Bytes)

See Note 1

I/O

010 (WriteData)

Byte/Word

See Note 1

First quadword

000

010

100

110

Second quadword

001

011

101

111

Third quadword

010

000

110

100

Fourth quadword

011

001

111

101

Fifth quadword

100

110

000

010