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backend: Drop the redundant ready term from the write busy signal - #265
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Every write unit only raises w_dp_ready_o while w_dp_valid_i is set, so the OR adds no information. It did add a combinational path from the write port ready into the backend busy and compute config stall, which closes a structural loop through a downstream AXI-to-OBI converter.
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pulp-platform/iDMA#265 is now only the write busy change. Pin its new deploy commit (c7f0456, on dc4ed2b). SpyGlass still reports 0 CombLoop on mem_tile_small and mem_tile_large.
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w_dp_busy_o = w_dp_valid_i | w_dp_ready_odrops thew_dp_ready_oterm. Every write unit (and the multi-portcc_stream_fork) only raises ready while valid is set, so the OR changes nothing, but it created a path from the write port ready into busy and the compute config stall. Together with pulp-platform/axi_obi#7 this removes the structural combinational loops SpyGlass reports (CombLoop) on the gwaihir mem tiles, whereidma_reg64_2d->idma_nd_midend->idma_backend_rw_axidrives anaxi_to_obi; with both,mem_tile_smallandmem_tile_largereport 0. None of the loops can be sensitized. No area or latency change; formally equivalent for every backend.