Hardware
/
litex
mirror of https://github.com/enjoy-digital/litex.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

doc/bus/CSR: add automatic CSR name info

This commit is contained in:
Sebastien Bourdeauducq 2013-07-22 16:47:49 +02:00
parent fe18397acc
commit aef78b2395
1 changed files with 2 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
doc/bus.rst
View File

@ -52,6 +52,8 @@ The lowest-level description of a register is provided by the ``CSR`` class, whi
* ``re``, which is the strobe signal for ``r``. It is active for one cycle, after or during a write from the bus. ``r`` is only valid when ``re`` is high. * ``re``, which is the strobe signal for ``r``. It is active for one cycle, after or during a write from the bus. ``r`` is only valid when ``re`` is high.
* ``w``, which must provide at all times the value to be read from the bus. * ``w``, which must provide at all times the value to be read from the bus.
Names of CSRs can be omitted if they can be extracted from the variable name. When using this automatic naming feature, prefixes ``_``, ``r_`` and ``_r_`` are removed.
Compound CSRs (which are transformed into ``CSR`` plus additional logic for implementation) provide additional features optimized for common applications. Compound CSRs (which are transformed into ``CSR`` plus additional logic for implementation) provide additional features optimized for common applications.
The ``CSRStatus`` class is meant to be used as a status register that is read-only from the CPU. The user design is expected to drive its ``status`` signal. The advantage of using ``CSRStatus`` instead of using ``CSR`` and driving ``w`` is that the width of ``CSRStatus`` can be arbitrary. Status registers larger than the bus word width are automatically broken down into several ``CSR`` registers to span several addresses. Be careful that the atomicity of reads is not guaranteed. The ``CSRStatus`` class is meant to be used as a status register that is read-only from the CPU. The user design is expected to drive its ``status`` signal. The advantage of using ``CSRStatus`` instead of using ``CSR`` and driving ``w`` is that the width of ``CSRStatus`` can be arbitrary. Status registers larger than the bus word width are automatically broken down into several ``CSR`` registers to span several addresses. Be careful that the atomicity of reads is not guaranteed.