When implementing concepts such as partition pins or deliberately split
nets, there's a need for something that looks like a cell (starts/ends
routing with pins on nets, has timing data) but isn't mapped to a fixed
bel in the architecture, but instead can have pin mappings defined at
runtime.
The PseudoCell allows this by providing an alternate, virtual-function
based API for such cells. When a cell has `pseudo_cell` used, instead of
calling functions such as getBelPinWire, getBelLocation or getCellDelay
in the Arch API; such data is provided by the cell itself, fully
flexible at runtime regardless of arch, via methods on the PseudoCell
implementation.
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>
Clustering greatly helps the placer to identify and pack together
specific cells at the same site (e.g. LUT+FF), or cells that are chained through
dedicated interconnections (e.g. CARRY CHAINS)
Signed-off-by: Alessandro Comodi <acomodi@antmicro.com>
Previous pseudo pips were the same cost as regular pips, but this is
definitely too fast, and meant that the router was prefering them.
Signed-off-by: Keith Rothman <537074+litghost@users.noreply.github.com>
This prevents the general router from routing through sites, which is
not legal in FPGA interchange.
Signed-off-by: Keith Rothman <537074+litghost@users.noreply.github.com>
- Finishes implementation of SiteArch::nameOfPip and SiteArch::nameOfWire
- Adds "explain_bel_status", which should be an exhaustive diagnostic
of the status of a BEL placement.
Signed-off-by: Keith Rothman <537074+litghost@users.noreply.github.com>
If get_net_type was called before the driver was placed, it could return
the wrong value.
Signed-off-by: Keith Rothman <537074+litghost@users.noreply.github.com>
For now just implements some inspection capabilities, and the site
router (for now) avoids inverted paths.
Signed-off-by: Keith Rothman <537074+litghost@users.noreply.github.com>
Currently the lookahead is disabled by default because of the time to
compute and RAM usage. However it does appear to work reasonably well
in testing. Further effort is required to lower RAM usage after initial
computation, and explore trade-off for cheaper time to compute.
Signed-off-by: Keith Rothman <537074+litghost@users.noreply.github.com>
