Update coding.md

Signed-off-by: D. Shah <dave@ds0.me>
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D. Shah 2021-02-03 10:42:46 +00:00
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@ -28,6 +28,8 @@ Additionally to this; architectures provide functions for checking the availabil
- Pips that represent LUT permutation are not available when the LUT is in memory mode
- only a certain total number of pips in a switchbox can be used at once due to power supply limitations
As well as implementing all of the standard [Arch API](archapi.md) functions; arches may include their own helper functions for various purposes. By convention these are in `snake_case`, to distinguish them from the `camelCase` Arch API functions.
## `IdString`s
To avoid the high cost of using strings as identifiers directly; almost all "string" identifiers in nextpnr (such as cell names and types) use an indexed string pool type named `IdString`. Unlike Yosys, which has a global garbage collected pool, nextpnr has a per-Context pool without any garbage collection.