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Figure 7-1
Mailbox Data Structure
63
QW 0
MBZ
QW 1
QW 2
QW 3
QW 4
QW 5
QW 6
QW 7
Table 7-15 gives the description of the mailbox data structure fields.
Table 7-15 Mailbox Data Structure Description
QW
Bit(s)
Name
<29:0>
CMD
0
<30>
B
<31>
W
<39:32>
MASK
<55:48>
HOSE
1
<63:0>
RBADR
2
<63:0>
WDATA
48 47
40 39
56
55
MBZ
MASK
HOSE
RBADR <63:0>
WDATA <63:0>
UNPREDICTABLE
RDATA <63:0>
UNPREDICTABLE
UNPREDICTABLE
Description
Remote Bus Command. Controls the remote bus operation
and can include fields such as address only, address width, and
data width. See Alpha SRM.
Remote Bridge Access. If set, the command is a special or
diagnostic command directed to the remote side. See Alpha
SRM.
Write Access. If set, the remote bus operation is a write.
Disable Byte Mask. Disables bytes within the remote bus ad-
dress. Mask bit <i> set causes the corresponding byte to be dis-
abled. For example, data byte 1 will NOT be written to the re-
mote address if MASK bit <33> is set. See Alpha SRM.
Hose. Specifies the remote bus to be accessed. Bridges can
connect to up to 256 remote buses.
Remote Bus Address. Contains the target address of the de-
vice on the remote bus. See Alpha SRM.
Write Data. For write commands, contains the data to be
written. For read commands, the field is not used by the
bridge.
32 31
30
29
CMD
W
B
STATUS
2
1
0
E
D
R
O
R
N
BXB-0174 C-94
System Registers 7-33
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