archapi: Add new API for global constant routing #1228
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Signed-off-by: gatecat <[email protected]>
Signed-off-by: gatecat <[email protected]>
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High-fanout dedicated global constant routing has been a weak spot in nextpnr, and a previous complexity in e.g. Xilinx support, where it necessitated complex virtual routing structures so the general routers could route them efficiently.
This removes all the arch complexity by allowing wires to be tagged as having a constant value, and therefore creates a simplified backwards routing problem for constants, allowing such wires to have multiple sources.
This should also solve some of the performance problems with router1 for nextpnr-nexus.