mem: Just-in-time write scheduling in DRAM controller

This patch removes the untimed while loop in the write scheduling
mechanism and now schedule commands taking into account the minimum
timing constraint. It also introduces an optimization to track write
queue size and switch from writes to reads if the number of write
requests fall below write low threshold.

1 files changed, 9 insertions, 3 deletions

diff --git a/src/mem/SimpleDRAM.py b/src/mem/SimpleDRAM.py
index 81bb0ff42..c450f8992 100644
--- a/src/mem/SimpleDRAM.py
+++ b/src/mem/SimpleDRAM.py
@@ -69,12 +69,18 @@ class SimpleDRAM(AbstractMemory):
     port = SlavePort("Slave port")
 
     # the basic configuration of the controller architecture
-    write_buffer_size = Param.Unsigned(32, "Number of read queue entries")
-    read_buffer_size = Param.Unsigned(32, "Number of write queue entries")
+    write_buffer_size = Param.Unsigned(32, "Number of write queue entries")
+    read_buffer_size = Param.Unsigned(32, "Number of read queue entries")
 
     # threshold in percent for when to trigger writes and start
     # emptying the write buffer as it starts to get full
-    write_thresh_perc = Param.Percent(70, "Threshold to trigger writes")
+    write_high_thresh_perc = Param.Percent(70, "Threshold to trigger writes")
+
+    # threshold in percentage for when to stop writes if the read
+    # queue has an entry. An optimisaton to give reads priority if
+    # sufficient number of writes are scheduled and write queue has
+    # sufficient number of free entries
+    write_low_thresh_perc = Param.Percent(0, "Threshold to stop writes")
 
     # scheduler, address map and page policy
     mem_sched_policy = Param.MemSched('frfcfs', "Memory scheduling policy")