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Table 15: Sideband Signals in pcie(n)_m_axis_cq_tuser (512-bit Interface)
Bit Index
Name
Width
Description
7:0
first_be[7:0]
8
Byte enables for the first Dword of the payload. first_be[3:0]
reflects the setting of the First Byte Enable bits in the
Transaction-Layer header of the first TLP in this beat; and
first_be[7:4] reflects the setting of the First Byte Enable bits
in the Transaction-Layer header of the second TLP in this
beat. For Memory Reads and I/O Reads, the 4 bits indicate
the valid bytes to be read in the first Dword. For Memory
Writes and I/O Writes, these bits indicate the valid bytes in
the first Dword of the payload. For Atomic Operations and
Messages with a payload, these bits are set to all 1s.
Bits [7:4] of first_be are valid only when straddle is enabled
on the CQ interface. When straddle is disabled, these bits
are permanently set to 0s.
This field is valid in the first beat of a packet. first_be[3:0] is
valid when pcie(n)_m_axis_cq_tvalid and is_sop[0] are both
asserted High. first_be[7:4] is valid when
pcie(n)_m_axis_cq_tvalid and is_sop[1] are both asserted
High.
15:8
last_be[7:0]
8
Byte enables for the last Dword of the payload. last_be[3:0]
reflects the setting of the Last Byte Enable bits in the
Transaction-Layer header of the first TLP in this beat; and
last_be[7:4] reflects the setting of the Last Byte Enable bits
in the Transaction-Layer header of the second TLP in this
beat. For Memory Reads, the 4 bits indicate the valid bytes
to be read in the last Dword of the block of data. For
Memory Writes, these bits indicate the valid bytes in the
ending Dword of the payload. For Memory Reads and Writes
of one DW transfers and zero length transfers, these bits
should be 0s. For Atomic Operations and Messages with a
payload, these bits are set to all 1s.
Bits [7:4] of last_be are valid only when straddle is enabled
on the CQ interface. When straddle is disabled, these bits
are permanently set to 0s.
This field is valid in the first beat of a packet. last_be[3:0] is
valid when pcie(n)_m_axis_cq_tvalid and is_eop[0] are both
asserted High. last_be[7:4] is valid when
pcie(n)_m_axis_cq_tvalid and is_eop[1] are both asserted
High.
79:16
byte_en[63:0]
64
The user logic can optionally use these byte enable bits to
determine the valid bytes in the payload of a packet being
transferred The assertion of bit i of this bus during a
transfer indicates to the user logic that byte i of the
pcie(n)_m_axis_cq_tdata bus contains a valid payload byte.
This bit is not asserted for descriptor bytes.
Although the byte enables can be generated by user logic
from information in the request descriptor (address and
length), as well as the settings of the first_be and last_be
signals, the user logic has the option of using these signals
directly instead of generating them from other interface
signals.
When the payload size is more than 2 Dwords (8 bytes), the
first bits on this bus for the payload are always contiguous.
When the payload size is 2 Dwords or less, the first bits
might be non-contiguous.
For the special case of a zero-length memory write
transaction defined by the PCI ExpressSpecifications, the
byte_en bits are all 0 when the associated 1 Dword payload
is being transferred.
Chapter 3: Product Specification
PG346 (v3.3) November 16, 2022
CPM Mode for PCI Express
56