mirror of https://github.com/YosysHQ/nextpnr.git
af79b7775c
The negotiated-congestion router can spin without converging on designs where (a) the architecturally optimal wire is genuinely unavailable, (b) the cost gradient between two near-equivalent candidates is too shallow to settle, or (c) a placer choice has fenced off the legal binding space and the failure won't surface until bind_and_check_all() actually runs. Today the main loop has no upper bound on iterations and bind_and_check_all() is only ever called on full convergence, so a stuck design loops forever while logging "archfail=NA" every iteration. Three small, opt-in safety hatches: 1. Hard iteration ceiling -- `cfg.max_router_iters` (default 2000). When reached, log a warning, bind what we have, and break the loop instead of spinning. 2. Stall detection -- `cfg.stall_iter_limit` (default 50). Watch (overused_wires, total_wire_overuse) across consecutive iterations. When both stay unchanged for stall_iter_limit iterations, first try resetting `curr_cong_weight` back to `cfg.init_curr_cong_weight` (once) to escape a local minimum. If the stall persists after the reset, break with a best-effort binding rather than continuing to loop. 3. Periodic validity check -- `cfg.bind_check_interval` (default 100). Even when `overused_wires > 0`, call bind_and_check_all() every `bind_check_interval` iterations so architectural impossibilities surface early instead of being silently masked by `archfail=NA`. All three are fully configurable via context settings (`router2/maxRouterIters`, `router2/stallIterLimit`, `router2/bindCheckInterval`). Defaults preserve existing behaviour for designs that converge promptly (well under 2000 iterations and never stall for 50 in a row), and the new break paths only fire on pathological cases that would otherwise loop forever. No new options exposed at the CLI; defaults are sized for typical designs and out-of-the-box behaviour is unchanged. |
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| .. | ||
| kernel | ||
| place | ||
| route | ||
| CMakeLists.txt | ||
| version.h.in | ||