Arria V Avalon-ST Interface for PCIe Solutions User Guide
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4.1.2.3. Data Alignment and Timing for the 128‑Bit Avalon‑ST TX Interface
The following figure shows the mapping of 128-bit Avalon-ST TX packets to PCI Express TLPs for a three dword header with qword aligned addresses. Assertion of tx_st_empty in an rx_st_eop cycle indicates valid data in the lower 64 bits of tx_st_data.
The following figure shows the mapping of 128-bit Avalon-ST TX packets to PCI Express TLPs for a 3 dword header with non-qword aligned addresses. It also shows tx_st_err assertion.
The following figure shows the mapping of 128-bit Avalon-ST TX packets to PCI Express TLPs for a four dword header TLP with non-qword aligned addresses. In this example, tx_st_empty is low because the data ends in the upper 64 bits of tx_st_data.
The following figure illustrates back‑to‑back transmission of 128‑bit packets with idle dead cycles between the assertion of tx_st_eop and tx_st_sop.
The following figure illustrates the timing of the TX interface when the Arria V Hard IP for PCI Express pauses the Application Layer by deasserting tx_st_ready. Because the readyLatency is two cycles, the Application Layer deasserts tx_st_valid after two cycles and holds tx_st_data until two cycles after tx_st_ready is reasserted