Single-cycle bypass when there is no contention on memory arbiter.

2 files changed, 11 insertions, 1 deletions

diff --git a/PLAN b/PLAN
index 759042c..938c85b 100644
--- a/PLAN
+++ b/PLAN
@@ -1,4 +1,3 @@
-0. figure out a way to add a single-cycle bypass to the arbiter
 1. add pdp-8 instruction cache
 2. add pdp-8 data cache
 3. add global shared cache
diff --git a/hdl/mem_arbiter.sv b/hdl/mem_arbiter.sv
index e39317d..854867f 100644
--- a/hdl/mem_arbiter.sv
+++ b/hdl/mem_arbiter.sv
@@ -62,6 +62,17 @@ module mem_arbiter
                 end
             end
 
+            if (hold_valid != 0 && !ram_valid) begin
+                for (int i = 0; i < `NUM_PDPS+1; ++i) begin
+                    if (hold_valid == 1 << i) begin
+                        ram_valid = 1;
+                        ram_data = hold_data[i];
+                        hold_valid[i] = 0;
+                        break;
+                    end
+                end
+            end
+
             if (hold_valid != 0 && (selector_stale || !ram_valid)) begin
                 for (int i = 0; i < `NUM_PDPS+1; ++i) begin
                     automatic int j = selector + i;