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| author | gatecat <gatecat@ds0.me> | 2021-12-19 16:41:34 +0000 |
|---|---|---|
| committer | gatecat <gatecat@ds0.me> | 2021-12-19 17:15:15 +0000 |
| commit | ddb084e9a8a0cba10536951236cde824526e8071 (patch) | |
| tree | d03ba5688367cb476a06b19d04ca78d0352afce3 /docs | |
| parent | 56d550733346000584b9490fac0953fe07124035 (diff) | |
| download | nextpnr-ddb084e9a8a0cba10536951236cde824526e8071.tar.gz nextpnr-ddb084e9a8a0cba10536951236cde824526e8071.tar.bz2 nextpnr-ddb084e9a8a0cba10536951236cde824526e8071.zip | |
archapi: Use arbitrary rather than actual placement in predictDelay
This makes predictDelay be based on an arbitrary belpin pair rather
than a arc of a net based on cell placement. This way 'what-if'
decisions can be evaluated without actually changing placement;
potentially useful for parallel placement.
A new helper predictArcDelay behaves like the old predictDelay to
minimise the impact on existing passes; only arches need be updated.
Signed-off-by: gatecat <gatecat@ds0.me>
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/archapi.md | 2 | ||||
| -rw-r--r-- | docs/coding.md | 2 |
2 files changed, 2 insertions, 2 deletions
diff --git a/docs/archapi.md b/docs/archapi.md index f2571f08..5034d7d1 100644 --- a/docs/archapi.md +++ b/docs/archapi.md @@ -517,7 +517,7 @@ result, and for that estimate it is considered more acceptable to return a slightly too high result and it is considered less acceptable to return a too low result (thus "low upper bound"). -### delay\_t predictDelay(const NetInfo \*net\_info, const PortRef &sink) const +### delay\_t predictDelay(BelId src_bel, IdString src_pin, BelId dst_bel, IdString dst_pin) const Return a reasonably good estimate for the total `maxDelay()` delay for the given arc. This should return a low upper bound for the fastest route for that arc. diff --git a/docs/coding.md b/docs/coding.md index dc09bb3f..db2ec079 100644 --- a/docs/coding.md +++ b/docs/coding.md @@ -80,7 +80,7 @@ As nextpnr allows arbitrary constraints on bels for more advanced packer-free fl There are several routes for timing information in the placer: - sink `PortRef`s have a `budget` value annotated by calling `assign_budget` which is an estimate of the maximum delay that an arc may have - sink ports can have a criticality (value between 0 and 1 where 1 is the critical path) associated with them by using `get_criticalities` and a `NetCriticalityMap` - - `predictDelay` returns an estimated delay for a sink port based on placement information + - `predictDelay` and its derivative `predictArcDelay` returns an estimated delay for a sink port based on placement information ### Bel Buckets |