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Table 6-12 UPCTL<3:0> Encoding
Table 6-13 shows the information given by the hose status signals.
6.6.4 Hose Packet Specifications
The packet types are different for each hose because the nature of infor-
mation sent through the Up Hose (from I/O to CPU or memory) differs
from the one sent through the Down Hose (from CPU or memory to I/O).
Most of the data transferred by I/O to and from memory is actual data
such as disk blocks and messages from terminals. Most of the data trans-
ferred by CPUs to and from I/O devices is control and status information.
6.6.4.1
Down Hose Packet Specifications
During the first cycle of a Down Hose packet, a packet type command field
is encoded into DND<15:11> by the I/O port. These bits indicate the type
of packet being transmitted across the Down Hose. The codes for the
packet types are given in Table 6-14.
UPCTL<3:0>
Meaning
First Hose Cycle of a Packet
Packet Type
DMA Read
0001
IREAD
0010
Mailbox Status Return
0100
0101
DMA Unmasked Write W/Data
DMA Masked Write W/Data
0111
INTR/IDENT
1000
Window Write Status
1100
Dense Window Read Return
1101
Sparse Window Read Return
1110
Data Cycles of a DMA Masked Write Packet
2
Mask
UPD<7:0> are valid
0001
UPD<15:8> are valid
0010
UPD<23:16> are valid
0100
UPD<31:24> are valid
1000
UPD<31:0> are valid
1111
1 All other UPCTL<3:0> packet type codes are reserved and will cause an Illegal Packet
Error when detected by the I/O port.
2 Any combination of mask bits can be used. The table simply attempts to show the rela-
tionship between UPCTL<3:0> lines and the bytes they mask.
1
I/O Port 6-39
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