6–18
Chapter 6: IP Core Interfaces
Avalon-ST TX Interface
Arria V GZ Hard IP for PCI Express
November 2012
Altera Corporation
1
I
valid
Clocks
tx_st_data
to the core when
tx_st_ready
is also
asserted. Between
tx_st_sop
and
tx_st_eop
,
tx_st_valid
must not be deasserted in the middle of a TLP except in response
to
tx_st_ready
deassertion. When
tx_st_ready
deasserts,
this signal must deassert within 1 or 2 clock cycles. When
tx_st_ready
reasserts, and
tx_st_data
is in mid-TLP, this
signal must reassert within 2 cycles. Refer to
for the timing of this signal.
For 256-bit data, when you turn on
Enable multiple packets per
cycle
, the following correspondences apply:
■
bit 1 applies to
tx_st_data[255:128]
■
bit 0 applies to
tx_st_data[127:0]
To facilitate timing closure, Altera recommends that you register
both the
tx_st_ready
and
tx_st_valid
signals. If no other
delays are added to the ready-valid latency, the resulting delay
corresponds to a
readyLatency
of 2.
tx_st_empty[1:0]
2
I
empty
Indicates the number of qwords that are empty during cycles that
contain the end of a packet. When asserted, the empty dwords
are in the high-order bits. Valid only when
tx_st_eop
is
asserted.
Not used when
tx_st_data
is 64 bits. For 128-bit data, only bit
0 applies and indicates whether the upper qword contains data.
For 256-bit data, both bits are used to indicate the number of
upper words that contain data, resulting in the following
encodings for the 128-and 256-bit interfaces:
128-Bit interface:
tx_st_empty
= 0,
tx_st_data[127:0]
contains valid data
tx_st_empty
= 1,
tx_st_data[63:0]
contains valid data
256-bit interface:
tx_st_empty
= 0,
tx_st_data[255:0]
contains valid data
tx_st_empty
= 1,
tx_st_data[191:0]
contains valid data
tx_st_empty
= 2,
tx_st_data[127:0]
contains valid data
tx_st_empty
= 3,
tx_st_data[63:0]
contains valid data
For 256-bit data, when you turn on
Enable multiple packets per
cycle
, the following correspondences apply:
■
bit 1 applies to the eop occurring in rx_st_data[255:128]
■
bit 0 applies to the eop occurring in rx_st_data[127:0]
When the TLP ends in the lower 128bits, the following equations
apply:
■
tx_st_eop[0]=1 & tx_st_empty[0]=0
,
tx_st_data[127:0]
contains valid data
■
tx_st_eop[0]=1 & tx_st_empty[0]=1
,
tx_st_data[63:0]
contains valid data,
tx_st_data[127:64]
is empty
Table 6–5. 64-, 128-, or 256-Bit Avalon-ST TX Datapath (Part 2 of 4)
Signal
Width
Dir
Avalon-ST
Type
Description