From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Sat, 16 Apr 2022 15:26:33 +0000 (+0100)
Subject: select width is data_width // data granularity.
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=38b888ff9dc612dabd4df9382f9bdd4c4e1e65d2;p=soc.git

select width is data_width // data granularity.
(common mistake to make, confused the hell out of me too)
---

diff --git a/src/soc/bus/wb_async.py b/src/soc/bus/wb_async.py
index 6775427f..9c7b4e2c 100644
--- a/src/soc/bus/wb_async.py
+++ b/src/soc/bus/wb_async.py
@@ -102,7 +102,11 @@ class WBAsyncBridge(Elaboratable):
                             # Parameters
                             p_ADDR_WIDTH=self.address_width,
                             p_DATA_WIDTH=self.data_width,
-                            p_SELECT_WIDTH=self.granularity,
+                            # width of select is the data width
+                            # *divided* by the data granularity.
+                            # data_width=32-bit, data granularity=8-bit,
+                            # select_width ==> 32/8 ==> 4
+                            p_SELECT_WIDTH=self.data_width//self.granularity,
 
                             # Clocks/resets
                             i_wbm_clk=self.wb_mclk,