4.3. Picking the Right Number of TCP Cores
In typical software systems, the cost of opening a TCP connection is quite CPU expensive, and may take a long time because of RTT and processing times in the operating system. Therefore, most software driven systems keep a TCP connection alive “forever” rather than closing it. In software, the low costs of system RAM for storing each TCP connection’s state are not worth the CPU processing costs.
For NPAP, each TCP connection which is open at the same time requires a dedicated TCP Core – which costs FPGA / ASIC resources. However, if RTT is low such as in a LAN, and with the very low costs of opening and closing a TCP connection in NPAP (a few hundred FPGA clock cycles), “time sharing” TCP Cores can save a lot of FPGA resources without any negatives. Please refer to the MLE Technical Brief TB20201203 “Deterministic Networking with TSN-10/25/50/100G” for more information on “time sharing” TCP Cores.
Typically, FPGA routing is a key limiting factor: The more TCP Cores you instantiate, the more on-chip AXI-Stream FPGA routing congestion you will see, the harder it is to achieve timing closure. As a rule of thumb, more than 20 TCP Cores may cause FPGA routing issues (obviously depending on your FPGA device and toolchain).
Likely On-Chip Routing Issue:
To read the full content, please log in or register as an MLE Developer Zone Member.