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| author | gatecat <gatecat@ds0.me> | 2022-06-23 18:48:31 +0100 |
|---|---|---|
| committer | gatecat <gatecat@ds0.me> | 2022-07-08 14:30:57 +0200 |
| commit | 09e388f453d9cf998391495349c88e5478b62e34 (patch) | |
| tree | 004f2b14ed5a3b0584c4998d9f0a5598cc52ab28 /docs | |
| parent | 86396c41d64d2583ec1dffca4298e83d927f0762 (diff) | |
| download | nextpnr-09e388f453d9cf998391495349c88e5478b62e34.tar.gz nextpnr-09e388f453d9cf998391495349c88e5478b62e34.tar.bz2 nextpnr-09e388f453d9cf998391495349c88e5478b62e34.zip | |
netlist: Add PseudoCell API
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.
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/netlist.md | 16 |
1 files changed, 15 insertions, 1 deletions
diff --git a/docs/netlist.md b/docs/netlist.md index 5d8ca572..43a96dde 100644 --- a/docs/netlist.md +++ b/docs/netlist.md @@ -25,10 +25,24 @@ Other structures used by these basic structures include: - `params` and `attrs` store parameters and attributes - from the input JSON or assigned in flows to add metadata - by mapping from parameter name `IdString` to `Property`. - `cluster` is used to specify that the cell is inside a placement cluster, with the details of the placement within the cluster provided by the architecture. - `region` is a reference to a `Region` if the cell is constrained to a placement region (e.g. for partial reconfiguration or out-of-context flows) or `nullptr` otherwise. + - `pseudo_cell` is an optional pointer to an implementation of the pseudo-cell API, used for cells implementing virtual functions such as partition pins without a mapped bel. `bel` will always be `BelId()` for pseudo-cells. + +## PseudoCellAPI + +Pseudo-cells can be used to implement cells with runtime-defined cell pin to wire mappings. This means they don't have to be a fixed part of the architecture, example use cases could be for implementing partition pins for partial reconfiguration regions; or forcing splits between SLRs. Pseudo-cells implement a series of virtual functions to provide data that for an ordinary cell would be obtained by calling 'bel' ArchAPI functions + +The pseudo-cell API is as follows: + - `Loc getLocation() const` : get an approximate location of the pseudocell + - `WireId getPortWire(IdString port) const`: gets the wire corresponding to a port (or WireId if it has no wire) + +It also implements functions for getting timing data, mirroring that of the Arch API: + - `bool getDelay(IdString fromPort, IdString toPort, DelayQuad &delay) const` + - `TimingPortClass getPortTimingClass(IdString port, int &clockInfoCount) const` + - `TimingClockingInfo getPortClockingInfo(IdString port, int index) const` ## NetInfo -`NetInfo` instances have the following fields: +`NetInfo` instances have the following fields:\ - `name` is the IdString name of the net - for nets with multiple names, one name is chosen according to a set of rules by the JSON frontend - `hierpath` is name of the hierarchical cell containing the instance, for designs with hierarchy |