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Table 6-29 DMA Masked Write Packet Description
Field
Clock 1, <31:24>
Clock 1, <23:11>
Clock 1, <10:8>
Clock 1, <7:0>
Clock 2, <31:0>
Clocks 3 through 18
ADR<39:0> is the target address for the DMA masked write and must be
naturally aligned to length (LEN) of the DMA masked write.
Table 6-30 DMA Masked Write Packet Sizes
6-58 I/O Port
Description
Don't Care. These bits, which normally form the TAG field, are don't
care, since DMA Masked Write packets are disconnected and have no
corresponding return packet.
Are always zero.
The length field indicates the length of the packet. A DMA Masked
Write packet has three possible packet lengths: octaword, hexword, and
double hexword. However, the length code for the octaword packet may
be a longword code (001) or a quadword code (010). The length code is
defined this way to maintain consistency with the length code of the
DMA Read packet. Even though the length code may indicate a
longword or quadword, the I/O port treats the packet as a normal
octaword masked write packet and performs a masked write using an
octaword of data. The actual bytes of data in an octaword masked write
packet that get written to memory are selected by the byte mask bits and
not by the quadword or longword length code.
Therefore, when performing a longword or quadword transfer using an
octaword masked write packet, the I/O bus adapter must set the proper
mask bits to select the longword or quadword within the octaword that
will be written to memory. The I/O bus adapter must clear the remain-
ing mask bits of the octaword masked write packet to prevent the un-
used bytes of the octaword packet from being written to memory. See
Table 6-30 for DMA masked write packet sizes.
NOTE: Even though the mask bits may "mask out" a particular longword
of the packet, the parity across the hose must be good for all cycles of the
DMA Masked Write packet.
ADR<39:32> of the target address. See definition below.
ADR<31:0> of the target address. See definition below.
Data. One longword on each clock.
Length
Packet Data
Code
Length
Octaword
001
010
Octaword
Octaword
011
Hexword
000
Double hexword
100
Data Valid in
Up Hose Cycles
Packet
Required
Longword
6
Quadword
6
Octaword
6
Hexword
10
Double hexword
18
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