Dma Read Packet Description; Dma Read Packet Sizes - DEC AlphaServer 8200 Technical Manual

Table 6-25 DMA Read Packet Description
Field Description
The TAG<7:0> field allows the subsequent DMA Read Data Return packet
Clock 1, <31:24>
on the Down Hose to be associated with a DMA Read Data packet on the
Up Hose. The tag is generated by the I/O bus adapter.
Are always zero.
Clock 1, <23:11>
The length field indicates the length of the DMA read packet. A DMA
Clock 1, <10:8>
read packet has three possible packet lengths: octaword, hexword, and
double hexword. However, the length code for the octaword packet may
indicate that only a longword or quadword of data is requested. This
length code is looped back through the DMA Read Data Return packet and
allows the I/O bus adapter to use the length code to extract the correct
amount of information from the octaword DMA Read Data Return packet.
See Table 6-26 for DMA read packet sizes.
ADR<39:32> of the target address. See definition below.
Clock 1, <7:0>
ADR<31:0> of the target address. See definition below.
Clock 2, <31:0>
ADR<39:0> is the target address for the TLSB memory read. It must be
naturally aligned to length (LEN) code of the data being requested.
Table 6-26 DMA Read Packet Sizes
Length Packet Data
Code Length
Octaword
001
Octaword
010
011 Octaword
Hexword
000
Double hexword
100
1 ADR<3:0> are ignored by the I/O port.
Interlock Read
The interlock read (IREAD) packet is a request on the Up Hose from the
I/O bus adapter to the I/O port for a quadword data read transaction on
the TLSB bus. The transaction is similar to a normal DMA read except
the I/O port performs an atomic Read-Modify-Write operation to read the
data, set bit <0> of the target quadword, and write it back to TLSB mem-
ory. This hardware assist helps software obtain an interlock on the
quadword location. The unaltered read data is returned across the Down
Hose using a DMA Read Data Return packet as it would be for a normal
read.
This packet is supported by the Mailbox Only, I/O Window, Full, and Mem-
ory Channel variants of the hose protocol. Figure 6-26 shows the IREAD
packet.
Significant Wrapped TLSB
1
Address Bits Read
ADR<39:4> Yes, if ADR<5>=1
ADR<39:4> Yes, if ADR<5>=1
ADR<39:4> Yes, if ADR<5>=1
ADR<39:5> Yes, if ADR<5>=1
ADR<39:6> No
Data
Requested
Longword
Quadword
Octaword
Hexword
Double hexword
I/O Port 6-55