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Comment by sargun | Hacker News Reader

In the spec, they say the maximum acceptable network delay is 200ns. The smallest network delay is 5ns.

It is really hard to believe that OpenCAPI can achieve this short latency with 25Gbps per lane interface and off-chip connectivity.

Xilinx offers 25gbps single-lanes that can bond up to 4x to get IEEE 802.3-2012 spec compliance for free* with their suite. Sure, you're going to need to control those trace impedences and your board won't be something coming out of OSH Park, but those are definitely attainable speeds for the consumer (e.g., in the single-thousands of dollars; not 800k Cisco VXR tier-1 infrastructure).

You can configure it in CAUI-10 (10 lanes x 10.3125G) or CAUI-4 (4 lanes x 25.78125G), either way, it's been production-ready for quite some time now. (The docs have numbers, but trust me, you can get full throughput within that 200 ns).

There's even production Agilent off-the-shelf test equipment out there that can fully sample at those speeds (none of that over-sampling tomfoolery, we're talking live, Bill O'Reilly style).

In 1989, UltraSPARC had similar facilities (SBus) to push 100MBit between other Sun machines, so I mean, not too insane comparatively.

* Free with purchase of Virtex® UltraScale™ and Kintex® UltraScale FPGA required haha.

Thanks for the info.

I would like to search the term and understand how they can achieve 200ns latency. Maybe am I the only one who thinks 200ns latency as completion latency?

It sounds like 200ns is the upper expected network delay. If 9 network delays at 200ns are experienced, it'll retrain the link.

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