diff options
| -rw-r--r-- | common/router1.cc | 10 | ||||
| -rw-r--r-- | docs/faq.md | 3 |
2 files changed, 10 insertions, 3 deletions
diff --git a/common/router1.cc b/common/router1.cc index 0481a95e..adad37e9 100644 --- a/common/router1.cc +++ b/common/router1.cc @@ -666,12 +666,18 @@ struct Router1 WireId cursor = dst_wire; delay_t accumulated_path_delay = 0; + delay_t last_path_delay_delta = 0; while (1) { auto pip = visited[cursor].pip; if (ctx->debug) { - log(" node %s (%+.1f)\n", ctx->nameOfWire(cursor), - ctx->getDelayNS(ctx->estimateDelay(cursor, dst_wire)) - ctx->getDelayNS(accumulated_path_delay)); + delay_t path_delay_delta = ctx->estimateDelay(cursor, dst_wire) - accumulated_path_delay; + + log(" node %s (%+.2f %+.2f)\n", ctx->nameOfWire(cursor), ctx->getDelayNS(path_delay_delta), + ctx->getDelayNS(path_delay_delta - last_path_delay_delta)); + + last_path_delay_delta = path_delay_delta; + if (pip != PipId()) accumulated_path_delay += ctx->getPipDelay(pip).maxDelay(); accumulated_path_delay += ctx->getWireDelay(cursor).maxDelay(); diff --git a/docs/faq.md b/docs/faq.md index 63869240..7b358187 100644 --- a/docs/faq.md +++ b/docs/faq.md @@ -46,7 +46,8 @@ See [archapi.md](archapi.md) for a complete reference of the architecture API. ### Delay Estimates Each architecture must implement a `estimateDelay()` method that estimates the expected delay for a path from given `src` to `dst` wires. -*It is very important that this method slightly overestimates the expected delay.* Otherwise there will be performance issues with the router. +*It is very important that this method slightly overestimates the expected delay.* Furthermore, it should overestimate the expected delay +by a slightly larger margin for longer paths than for shorter paths. Otherwise there will be performance issues with the router. The delays estimates returned by that method should also be as fine-grain as possible. It definitely pays off to spend some time improving the `estimateDelay()` for your architecture once implementing small designs work. |