From 11601c336526f5b15587d45895048def4d8114a3 Mon Sep 17 00:00:00 2001
From: Kia <kia@special-circumstanc.es>
Date: Wed, 3 Mar 2021 15:44:51 -0700
Subject: [PATCH] continue work on gear box
---
gearbox.py | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/gearbox.py b/gearbox.py
index fb3b65e..a82bc01 100755
--- a/gearbox.py
+++ b/gearbox.py
@@ -86,7 +86,23 @@ class ArbitraryGearbox(Elaboratable):
# 2) there are in_width invalid bits in front of the write_ptr
+ # There are multiple cases for read_ptr and write_ptr:
+ # read_ptr < write_ptr. Here, the valid bits do not wrap, the invalid bits wrap.
+ # The valid bits are: inclusive [read_ptr, write_ptr) exclusive
+ # the invalid bits are inclusive [write_ptr, K) exclusive, union with inclusive [0, read_ptr) exclusive
+
+
+ # write_ptr < read_ptr. Here, the valid bits wrap, and the invalid bits do not wrap.
+ # The valid bits are: inclusive [read_ptr, K) exclusive, union with inclusive [0, write_ptr) exclusive
+ # the invalid bits are inclusive [write_ptr, read_ptr) exclusive
+
+ # Naturally, there is a tricky edge case which requires an extra bit (literally) of disambiguation.
+ # If write_ptr == read_ptr we don't know if the buffer is entirely full or entirely empty.
+
+ # If the last operation was a read, and we find write_ptr == read_ptr, we know it's empty
+ # If the last operation was a write, and we find write_ptr == read_ptr, we know it's full
+
return m
--
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