From: Florent Kermarrec <florent@enjoy-digital.fr>
Date: Fri, 19 Apr 2019 09:43:15 +0000 (+0200)
Subject: soc/interconnect/avalon: add description
X-Git-Tag: 24jan2021_ls180~1322
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=5a8115d9e1fcdc95328e20314c5a74332e42a4cc;p=litex.git

soc/interconnect/avalon: add description
---

diff --git a/litex/soc/interconnect/avalon.py b/litex/soc/interconnect/avalon.py
index edc2f6f1..883ddcf5 100644
--- a/litex/soc/interconnect/avalon.py
+++ b/litex/soc/interconnect/avalon.py
@@ -1,10 +1,20 @@
+"""Avalon support for LiteX"""
+
 from migen import *
 
 from litex.soc.interconnect import stream
 
-# AvalonST to/from Native --------------------------------------------------------------------------
+# Avalon-ST to/from native LiteX's stream ----------------------------------------------------------
+
+# In native LiteX's streams, ready signal has no latency (similar to AXI). In Avalon-ST streams the
+# ready signal has a latency: If ready is asserted on cycle n, then cycle n + latency is a "ready"
+# in the LiteX/AXI's sense) cycle. This means that:
+# - when converting to Avalon-ST, we need to add this latency on datas.
+# - when converting from Avalon-ST, we need to make sure we are able to store datas for "latency"
+# cycles after ready deassertion on the native interface.
 
 class Native2AvalonST(Module):
+    """Native LiteX's stream to Avalon-ST stream"""
     def __init__(self, layout, latency=2):
         self.sink = sink = stream.Endpoint(layout)
         self.source = source = stream.Endpoint(layout)
@@ -23,6 +33,7 @@ class Native2AvalonST(Module):
 
 
 class AvalonST2Native(Module):
+    """Avalon-ST Stream to native LiteX's stream"""
     def __init__(self, layout, latency=2):
         self.sink = sink = stream.Endpoint(layout)
         self.source = source = stream.Endpoint(layout)