145 lines
5.8 KiB
Markdown
145 lines
5.8 KiB
Markdown
# Litex Documentation: Document your LiteX SoC Automatically
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Litex lets you take a synthesized SoC and generate full
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register-level documentation. Additionally, it will generate `.svd` files,
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suitable for use with various header generation programs.
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## Required Software
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You must have `sphinx` and `sphinx.wavedrom` installed in order to build
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the documentation. These can be installed with pip:
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```
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$ pip3 install sphinxcontrib-wavedrom sphinx
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```
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## Usage
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To document your modules, import the `doc` module and call `doc.generate_docs(soc, path)`.
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You can also generate an SVD file. For example:
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```python
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import litex.soc.doc
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...
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soc = BaseSoC(platform)
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builder = Builder(soc)
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vns = builder.build()
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soc.do_exit(vns)
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doc.generate_docs(soc, "build/documentation")
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doc.generate_svd(soc, "build/software")
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```
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After you build your design, you will have a Sphinx documentation source available
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in the above directory. To build this into a target document, use `sphinx-build`.
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For example, if `sphinx-build` is in your path, you can run:
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`sphinx-build -M html build/documentation/ build/documentation/_build`
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`sphinx-build` may be located in `~/.local/bin/` depending on your installation environment.
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You can then verify the contents by opening the file `build/documentation/_build/html/index.html`
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## Documenting your Registers
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You can add documentation to your registers by defining your `CSRStorage` and `CSRStatus` registers with an additional `field` list. For example:
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```python
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self.bitbang = CSRStorage(4, fields=[
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CSRField("mosi", description="Output value for MOSI..."
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CSRField("clk", description="Output value for SPI CLK..."
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CSRField("cs_n", description="Output value for SPI C..."
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CSRField("dir", description="Sets the dir...", values=[
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("0", "OUT", "SPI pins are all output"),
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("1", "IN", "SPI pins are all input"),
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])
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], description="""Bitbang controls for SPI output. Only
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standard 1x SPI is supported, and as a result all
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four wires are ganged together. This means that it
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is only possible to perform half-duplex operations,
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using this SPI core.""")
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```
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There are several interesting properties here:
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* The first argument to a `CSRStorage` or `CSRStatus` is the bit width.
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* You can pass a list of `CSRField` objects, which will get turned into bit fields
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* Both `CSRStorage` and `CSRStatus` support a freeform `description` property that will be used to describe the overall register.
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A `CSRField` object has the following properties:
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* `name`: The short name of the register. This should be just a few characters long, as it will be used in the register diagram as well as accessor objects. **Required**
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* `size`: The size of this field. This is optional, and defaults to `1`
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* `offset`: The offset of this particular field. If unspecified, defaults to following the previous field. Use this to add gaps to your register definitions, for example to have reserved fields.
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* `reset`: If specified, the value of this field at reset. Defaults to `0`.
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* `description`: A textual description of this register. This is optional, but should be specified because it provides critical information to the user about what this field does.
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* `pulse`: If `True`, then this value is `1` only for one clock cycle after the user writes a `1` to this field. This is especially useful for `START` bits used to initiate operations, or `RESET` bits used to clear an operation.
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* `access`: The accessibility of this field. One of `CSRAccess.ReadWrite`, `CSRAccess.WriteOnly`, or `CSRAccess.ReadOnly`
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* `values`: If present, a list of tuples of values. The first field is the numeric value, with `x` for `don't care`. The second field, if present, is the short name of the value. The final field is a textual description of the value. For example:
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```python
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[
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("0b0000", "disable the timer"),
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("0b0001", "slow", "slow timer"),
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("0b1xxx", "fast timer"),
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]
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```
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## Further Module Documentation
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You can add additional documentation to your module with the `ModuleDoc` class. Add it to your base object.
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**To use further Module Documentation, your Module must inherit from `AutoDoc`**. For example:
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```python
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from litex.soc.integration.doc import AutoDoc, ModuleDoc
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class DocExample(Module, AutoCSR, AutoDoc):
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def __init__(self):
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self.mydoc = ModuleDoc("Some documentation")
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```
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You may pass a single string to the constructor, in which case the first line becomes the title, or you may pass a separate `title` and `body` parameters to the constructor. For example:
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```python
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self.intro = ModuleDoc("""Introduce ModuleDoc
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This is an example of how to document using ModuleDoc. An additional
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section will get added to the output documentation for this module,
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with the title ``Introduce ModuleDoc`` and with this paragraph
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as a body""")
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```
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Note that the default documentation format is `rst`. You can switch to markdown by passing `format="markdown"` to the constructor, however support is not very good.
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### External Documentation
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You can have external documentation by passing `file` to the constructor.
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For example:
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```python
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self.extra_doc = ModuleDoc(file="extra_doc.rst")
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```
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This will be included at build-time.
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### Using Python Docstrings
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You can also simply have your module inherit from `ModuleDoc`, in which case
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the documentation will be taken from the docstring. For example:
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```python
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from litex.soc.integration.doc import AutoDoc, ModuleDoc
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class DocExample(Module, AutoCSR, AutoDoc, ModuleDoc):
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"""
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Automatically Documented Module
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This module will be automatically documented, and included in the
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generated module documentation output. You can add additional
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ModuleDoc objects to this module, in order to add further subsections
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to the output docs.
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"""
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def __init__(self):
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pass
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```
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