Chapter 6: IP Core Interfaces
6–5
Avalon-ST RX Interface
November 2012
Altera Corporation
Arria V GZ Hard IP for PCI Express
rx_st_empty[1:0]
1, 2
O
empty
Indicates the number of empty qwords in
rx_st_data
. Not
used when
rx_st_data
is 64 bits. Valid only when
rx_st_eop
is asserted in 128-bit and 256-bit modes.
For 128-bit data, only bit 0 applies; this bit indicates whether
the upper qword contains data. For 256-bit data single packet
per cycle mode, both bits are used to indicate whether 0-3
upper qwords contain data, resulting in the following encodings
for the 128-and 256-bit interfaces:
128-Bit interface:
rx_st_empty
= 0,
rx_st_data[127:0]
contains valid data
rx_st_empty
= 1,
rx_st_data[63:0]
contains valid data
256-bit interface: single packet per cycle mode
rx_st_empty
= 0,
rx_st_data[255:0]
contains valid data
rx_st_empty
= 1,
rx_st_data[191:0]
contains valid data
rx_st_empty
= 2,
rx_st_data[127:0]
contains valid data
rx_st_empty
= 3,
rx_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:
■
rx_st_eop[0]=1 & rx_st_empty[0]=0
,
rx_st_data[127:0]
contains valid data
■
rx_st_eop[0]=1 & rx_st_empty[0]=1
,
rx_st_data[63:0]
contains valid data,
rx_st_data[127:64]
is empty
When TLP ends in the upper 128bits, the following equations
apply:
■
rx_st_eop[1]=1 & rx_st_empty[1]=0
,
rx_st_data[255:128]
contains valid data
■
rx_st_eop[1]=1 & rx_st_empty[1]=1
,
rx_st_data[191:128]
contains valid data,
rx_st_data[255:192]
is empty
rx_st_ready
1
I
ready
Indicates that the Application Layer is ready to accept data. The
Application Layer deasserts this signal to throttle the data
stream.
If
rx_st_ready
is asserted by the Application Layer on cycle
<n>,
then
<n +
readyLatency>
is a ready cycle, during which
the Transaction Layer may assert
valid
and transfer data.
The RX interface supports a
readyLatency
of 2 cycles.
Table 6–3. 64-, 128-, or 256-Bit Avalon-ST RX Datapath (Part 2 of 4)
Signal
Width
Dir
Avalon-ST
Type
Description