Janus is a hardware component specializing in moving data between uncached DRAM locations.
It comes in two pieces, each piece like part of the hardware that interfaces to fibers.
The first piece gets data from DRAM and is programmed via a structure much like a normal OHR.
The other piece deposits data in DRAM like the hardware that deposits incoming packets in DRAM.
I don’t know yet whether it should produce an IHR.
Janus can pose as a low latency down stream node to perform a prompt internal DRAM to DRAM transfer without the overhead of an error syndrome and without imposing a load on the cache.
It can run at maximum bandwidth yet taking low priority access to DRAM.
It can be used for two tragic purposes:
- For outgoing traffic on long high latency fiber, so as not to overstay the welcome of the payloads in the IPRs.
- To move stragglers caused to transmission errors out of the way of new incoming packets.
In either case Janus should either be agile with respect to output stream, or there should be multiple Januses.
There may be issues of priority among tasks as well as priority on DRAM requests.
Perhaps high latency links could use output streamers for sending data that did not require gather capability that we have assume otherwise.
Is there any advantage to this?
I don’t know.