Compaq EV68A Manual De Usuario
21264/EV68A Hardware Reference Manual
Cache and External Interfaces
4–37
System Port
point is the QW pointed to by the 21264/EV68A; however, some systems may find it
more beneficial to begin the transfer elsewhere. The system must always indicate the
starting point to the 21264/EV68A. The wrap order for subsequent QWs is interleaved.
more beneficial to begin the transfer elsewhere. The system must always indicate the
starting point to the 21264/EV68A. The wrap order for subsequent QWs is interleaved.
Table 4–29 defines the method for systems to specify wrap and deliver data.
Note 1:
Transfers to and from the 21264/EV68A have eight data cycles for a total
of eight quadwords. The starting point is defined by the system. The pre-
ferred 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 com-
mand. See Table 4–30 for the wrap order.
of eight quadwords. The starting point is defined by the system. The pre-
ferred 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 com-
mand. See Table 4–30 for the wrap order.
Note 2:
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.
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.
Table 4–29 System Wrap and Deliver Data
Source/
Destination
Destination
SysDc[4:2]
SysDc[1:0]
Size
Rules
Memory
100 (ReadData)
SysAddOut_L[5:4]
Block (64 Bytes)
See Note 1
Memory
101(ReadDataDirty)
SysAddOut_L[5:4]
Block (64 Bytes)
See Note 1
Memory
110 (ReadDataShared)
SysAddOut_L[5:4]
Block (64 Bytes)
See Note 1
Memory
111(Read DataShared/Dirty)
SysAddOut_L[5:4]
Block (64 Bytes)
See Note 1
Memory
010 (WriteData)
SysAddOut_L[5:4]
Block (64 Bytes)
See Note 1
I/O
100 (ReadData)
SysAddOut_L[5:4]
QW (8-64 Bytes)
See Note 1
I/O
100 (ReadData)
SysAddOut_L[4:3]
LW(4-32 Bytes)
See Note 2
I/O
100 (ReadData)
SysAddOut_L[4:3]
Byte/Word
See Note 2
I/O
010 (WriteData)
SysAddOut_L[5:4]
QW (8-64 Bytes)
See Note 1
I/O
010 (WriteData)
SysAddOut_L[5:4]
LW(4-32 Bytes)
See Note 1
I/O
010 (WriteData)
SysAddOut_L[5:4]
Byte/Word
See Note 1
Table 4–30 Wrap Interleave Order
PA Bits [5:3] of Transferred QW
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