From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Fri, 24 Jul 2020 15:10:54 +0000 (+0100)
Subject: add better comments on field_slice
X-Git-Tag: semi_working_ecp5~563
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=8915593ef29b253dc0b6af3d89e53a8b29474d19;p=soc.git

add better comments on field_slice
---

diff --git a/src/soc/consts.py b/src/soc/consts.py
index 40512121..48d5ddf5 100644
--- a/src/soc/consts.py
+++ b/src/soc/consts.py
@@ -9,10 +9,16 @@ def botchify(bekls, lekls):
 # Can't think of a better place to put these functions.
 # Return an arbitrary subfield of a larger field.
 def field_slice(msb0_start, msb0_end, field_width=64):
-    """Answers with a subfield slice of the signal r ("register"),
-    where the start and end bits use IBM conventions.  msb0_start < msb0_end.
-    The range specified is inclusive on both ends.
-    field_width specifies the total number of bits (not bits-1)
+    """field_slice
+
+    Answers with a subfield slice of the signal r ("register"),
+    where the start and end bits use IBM "MSB 0" conventions.
+
+    see: https://en.wikipedia.org/wiki/Bit_numbering#MSB_0_bit_numbering
+
+    * assertion: msb0_start < msb0_end.
+    * The range specified is inclusive on both ends.
+    * field_width specifies the total number of bits (note: not bits-1)
     """
     if msb0_start >= msb0_end:
         raise ValueError(