Chapter 6: IP Core Interfaces
6–27
ECRC Forwarding
November 2012
Altera Corporation
Arria V GZ Hard IP for PCI Express
Multiple Packets per Cycle
If you enable
Multiple Packets Per Cycle
under the
Systems Settings
heading, a TLP
can start on a 128-bit boundary. This mode supports multiple start of packet and end
of packet signals in a single cycle when the Avalon-ST interface is 256 bits wide.
illustrates this mode for a 256-bit Avalon-ST TX interface. In this figure
tx_st_eop[0]
and
tx_st_sop[1]
are asserted in the same cycle.Using this mode
increases the complexity of the Application Layer logic but results in higher
throughput, depending on the TX traffic.
Root Port Mode Configuration Requests
If your Application Layer implements ECRC forwarding, it should not apply ECRC
forwarding to Configuration Type 0 packets that it issues on the Avalon-ST interface.
There should be no ECRC appended to the TLP, and the
TD
bit in the TLP header
should be set to 0. These packets are processed internally by the Hard IP block and are
not transmitted on the PCI Express link.
ECRC Forwarding
On the Avalon-ST interface, the ECRC field follows the same alignment rules as
payload data. For packets with payload, the ECRC is appended to the data as an extra
dword of payload. For packets without payload, the ECRC field follows the address
alignment as if it were a one dword payload. Depending on the address alignment,
through
illustrate the position of the
through
illustrate the position of ECRC data for TX data. For packets with no payload data, the
ECRC position corresponds to the position of Data0 in these figures.
Figure 6–31. 256-Bit Avalon-ST TX Interface with Multiple Packets Per Cycle
tx_st_sop[0]
tx_st_eop[0]
tx_st_sop[1]
tx_st_eop[1]
tx_st_ready
tx_st_valid
tx_st_data[255:0]
12 ... 12...
12...
12...
12...
12...
12...
12...
00...
5A...
5A... 5A...
5A...
5A... 5A...
5A... 5A...
tx_st_empty[1:0]