Hi,
does anyone have serious plans to use more than one Sinara crate?
A crate already contains one Metlino and up to 12 Sayma cards, which
means 96 DAC and 96 ADC channels. A Metlino could also be connected to
several Kaslis (if the Kasli ends up being made).
Multi-crate configurations require slightly complicated gateware support
for DRTIO switches. The bandwidth between crates will also be limited to
10Gbps. Crossing each switch will incur 100ns-200ns of latency which
will manifest itself in two significant ways:
1) slower response times.
2) blocking the kernel CPU by twice the latency (round-trip) when it
needs to enquire about the space available in a remote RTIO FIFO.
There is currently a plan to support multi-crate in the hardware (this
future-proofing simply means adding some SFPs, essentially) but no plan
to support it in the gateware.
DRTIO switch support is also beneficial to the serial protocol between
the Sayma AMC and Sayma RTM FPGAs - the current plan is to use a dumb
protocol that doesn't have good timing resolution and is inefficient for
things like SPI transfers, essentially a more open version of Channel
Link II.
Sébastien
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