Update the FAQ and add doc on versioning (#1827)

* Update the FAQ and add doc on versioning
* Update modules.md

Co-authored-by: Megan Wachs <megan@sifive.com>

1 files changed, 35 insertions, 0 deletions

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+---
+layout: docs
+title:  "Versioning"
+section: "chisel3"
+---
+
+# Chisel Project Versioning
+
+Chisel and related projects follow a versioning scheme similar to [PVP](https://pvp.haskell.org/).
+Project versions are of the form `A.B.C` where `A.B` specifies the _Major_ version and `C` specifies the _Minor_ version.
+Projects maintain _binary compatibility_ between minor versions of the same major version.
+For example, a project compiled against Chisel3 version 3.4.0 can be used with Chisel3 version 3.4.2 or 3.4.15 without recompilation.
+
+# Compatible Versions
+
+Historically, due to a mistake in versioning with chisel-iotesters as well as some projects originating later than others,
+the compatible versions of Chisel-related projects has not been obvious.
+We are taking steps to improve the situation by bringing the major versions more in line (the `B` part in `A.B.C`),
+but the inconsistencies remain in previously published versions.
+
+Please use the following table to determine which versions of the related projects are compatible.
+In particular, versions of projects in this table were compiled against the version of any dependencies listed in the same row.
+For example, `chisel-iotesters` version 1.4 was compiled against `chisel3` version 3.3.
+
+| chisel3 | chiseltest | chisel-iotesters | firrtl | treadle | diagrammer | firrtl-interpreter<sup>2</sup> |
+| ------- | ---------- | ---------------- | ------ | ------- | ---------- | ----- |
+| 3.4     | 0.3        | 1.5              | 1.4    | 1.3     | 1.3        | 1.4 |
+| 3.3     | 0.2        | 1.4              | 1.3    | 1.2     | 1.2        | 1.3 |
+| 3.2     | 0.1<sup>1</sup>  | 1.3        | 1.2    | 1.1     | 1.1        | 1.2 |
+| 3.1     | -          | 1.2              | 1.1    | 1.0     | 1.0        | 1.1 |
+| 3.0     | -          | 1.1              | 1.0    | -<sup>3</sup> | -    | 1.0 |
+
+<sup>1</sup> chiseltest 0.1 was published under artifact name [chisel-testers2](https://search.maven.org/search?q=a:chisel-testers2_2.12) (0.2 was published under both artifact names)    
+<sup>2</sup> Replaced by Treadle, in maintenance mode only since version 1.1    
+<sup>3</sup> Treadle was preceded by the firrtl-interpreter