Altera Arria V Hard IP for PCI Express - Manual (Page 114)

7–16 Chapter 7: IP Core Interfaces
Arria V Hard IP for PCI Express
Arria V Hard IP for PCI Express December 2013 Altera Corporation
User Guide
tx_st_valid (1) 1 I valid
Clocks tx_st_data to the Hard IP when tx_st_ready is
also asserted. Between tx_st_sop and tx_st_eop ,
tx_st_valid can be asserted only if tx_st_ready is
asserted. 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 Figure 7–20 on
page 7–19 for the timing of this signal.
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 I empty
Indicates the number of qwords that are empty during
cycles that contain the end of a packet. When asserted, the
empty qwords are in the high-order bits. Valid only when
tx_st_eop is asserted.
Not used when tx_st_data is 64 bits. When asserted,
indicates that the upper qword is empty, does not contain
valid data.
tx_st_err 1 I error
Indicates an error on transmitted TLP. This signal is used to
nullify a packet. It should only be applied to posted and
completion TLPs with payload. To nullify a packet, assert
this signal for 1 cycle after the SOP and before the EOP.
When a packet is nullified, the following packet should not
be transmitted until the next clock cycle.
tx_st_err is not
available for packets that are 1 or 2 cycles long. The error
signal must be asserted while the valid signal is asserted.
Component Specific Signals
tx_fifo_empty 1 O
component
specific
When asserted high, indicates that the TX FIFO is empty.
tx_cred_datafccp 12 O
component
specific
Data credit limit for transmission of completions. Each
credit is 16 bytes.
tx_cred_datafcnp 12 O
component
specific
Data credit limit for transmission of non-posted requests.
Each credit is 16 bytes.
tx_cred_datafcp 12 O
component
specific
Data credit limit for transmission of posted writes. Each
credit is 16 bytes.
Table 7–4. 64- or 128-Bit Avalon-ST TX Datapath (Part 2 of 4)
Signal Width Dir
Avalon-ST
Type
Description