Crossbar Interfaces

A StreamIF connects exactly one master to one slave. When several producers must reach several consumers over one fabric, CrossBarIF is the switching version: nports_in inputs, nports_out outputs, and a routing function that decides which burst goes where.

Everything on the stream page about what you can move — raw words, an array, a schema — applies here unchanged; only the topology differs.

CrossBarIF routes bursts from nports_in input ports to nports_out output ports via a configurable routing function.

Classes

Class	Role	Key parameters
CrossBarIF	Interface	clk, bitwidth, latency_init, nports_in, nports_out, route_fn
CrossBarIFInput	Input (master) endpoint	bitwidth
CrossBarIFOutput	Output (slave) endpoint	bitwidth, rx_proc, queue_size

Endpoint names follow the pattern in_0, in_1, …, out_0, out_1, …

Routing function

The route_fn(words, port_in) -> port_out callable maps each burst to an output port. If not provided, the default is port_out = port_in % nports_out.

def route_by_first_word(words: Words, port_in: int) -> int:
    return int(words[0]) % nports_out

Example: 2×2 crossbar

from waveflow.hw.interface import CrossBarIF, CrossBarIFInput, CrossBarIFOutput

xbar = CrossBarIF(
    sim=sim,
    clk=clk,
    nports_in=2,
    nports_out=2,
    bitwidth=32,
    latency_init=2.0,
    route_fn=route_by_first_word,
)

xbar.bind("in_0",  src0.input_ep)
xbar.bind("in_1",  src1.input_ep)
xbar.bind("out_0", sink0.output_ep)
xbar.bind("out_1", sink1.output_ep)

The crossbar’s write(words, port_in) is called internally by CrossBarIFInput.write(words) — callers only need the input endpoint’s write method.

Each CrossBarIFOutput endpoint has the same run_proc() loop as StreamIFSlave and must be started before transfers are sent.

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How it lowers

Internal only, like stream-of-blocks: a CrossBarIF has no boundary kind and never becomes a port. It is the n × m stream fabric inside a design, and each of its edges lowers as the ordinary stream it is.

• HLS — Endpoint interfaces for the per-edge lowering; there is no crossbar object in the generated C++.
• BFM / XSI — none. Nothing here is a pin, so nothing here has a dual.