From e2fc3ed0717bf3b3cc7ee04106007f253e9dbccc Mon Sep 17 00:00:00 2001
From: Kia <kia@special-circumstanc.es>
Date: Sat, 14 Dec 2019 14:49:16 -0700
Subject: [PATCH] begin correction of the critical bug
---
stack.py | 32 ++++++++++++++++++++++++++++----
1 file changed, 28 insertions(+), 4 deletions(-)
diff --git a/stack.py b/stack.py
index 9582853..b489178 100644
--- a/stack.py
+++ b/stack.py
@@ -115,11 +115,33 @@ class InspectableStack(Elaboratable):
-# this subcomponent is NOT pipelined. It is fully combinatorial:
-# every clock cycle, it ingests the entire stack and reports all
-# the matches before the next clock cycle.
+# Hit Or Miss is the current rule lookup engine.
#
-# Further work should be dedicated towards exploring the design space
+# It is fully combinatorial; every cycle it ingests the current state
+# of the stack and the new item, and determines:
+#
+# 1. Fast Reject: Whether the new item can be immediately rejected.
+# This corresponds to a blank space in an LR parser table
+#
+# 2. Force Shift: Whether the new item must be shifted onto the stack
+# *without* looking at possible reduction rules to apply to the current
+# state of the stack.
+#
+# 3. Reduce Select: Which reduction rule applies to the current stack, and
+# if multiple rules apply, which rule to select.
+#
+# Note that this list is in decreasing priority -- if Fast Reject triggers
+# the results of Force Shift or Reduce Select are immaterial. Similarly, if
+# Force Shift triggers, we must ignore the results of Reduce Select.
+#
+# Fast Reject allows to, well, immediately reject invalid data and avoid
+# getting the stack in an invalid state. Force Shift allows the resolving of
+# Shift/Reduce conflicts -- otherwise, the parser would immediately reduce
+# everything it sees, as far as possible. Reduce Select resolves Reduce/Reduce
+# conflicts.
+
+
+# Further work will be dedicated towards exploring the design space
# to see whether LUT usage / timing can be optimized by splitting the
# lookup over several clock cycles -- since we can preselect the subset
# of relevant-to-our-interest rules based on what is *already* on the stack
@@ -179,6 +201,8 @@ class HitOrMiss(Elaboratable):
self.item_width = item_width
self.stack_depth = stack_depth
+ # Signals
+ self.new_item_in = Signal(item_width)
self.stack_view_in = Array([Signal(item_width) for _ in range(stack_depth)])
self.occupancy_bitmap_in = Signal(stack_depth)
--
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