From 8b790b79d9525aff2a3e03e4ee11396f377f679b Mon Sep 17 00:00:00 2001
From: Florent Kermarrec <florent@enjoy-digital.fr>
Date: Thu, 1 Jun 2023 09:48:35 +0200
Subject: [PATCH] frontend/avalon: Consider single access as a 1 word burst and
 simplify.

---
 litedram/frontend/avalon.py | 61 +++++++++++++++----------------------
 1 file changed, 25 insertions(+), 36 deletions(-)

diff --git a/litedram/frontend/avalon.py b/litedram/frontend/avalon.py
index 7fc2e85..3f66770 100644
--- a/litedram/frontend/avalon.py
+++ b/litedram/frontend/avalon.py
@@ -50,10 +50,10 @@ class LiteDRAMAvalonMM2Native(LiteXModule):
         # # #
 
         # Internal Signals.
-        burst_count     = Signal(9)
-        burst_write     = Signal()
-        address         = Signal(port.address_width)
-        address_offset  = Signal(port.address_width)
+        burst_count    = Signal(9)
+        burst_read     = Signal()
+        burst_address  = Signal(port.address_width)
+        address_offset = Signal(port.address_width)
         self.comb += address_offset.eq(base_address >> log2_int(port.data_width//8))
 
         # Write Data-path.
@@ -81,47 +81,36 @@ class LiteDRAMAvalonMM2Native(LiteXModule):
         ]
 
         # Control-Path.
-        self.fsm = fsm = FSM(reset_state="IDLE")
-        fsm.act("IDLE",
+        self.fsm = fsm = FSM(reset_state="SINGLE-ACCESS")
+        fsm.act("SINGLE-ACCESS",
             avalon.waitrequest.eq(1),
-            # Start of Access.
-            If(avalon.read | avalon.write,
-                NextValue(burst_count, avalon.burstcount),
-                NextValue(burst_write, avalon.write),
-                NextValue(address, avalon.address - address_offset),
-                # Burst Access.
-                If(avalon.burstcount > 1,
-                    If(avalon.read,
-                        avalon.waitrequest.eq(0)
-                    ),
-                    NextState("BURST")
-                # Single Access.
-                ).Else(
-                    port.cmd.addr.eq(avalon.address - address_offset),
-                    port.cmd.we.eq(avalon.write),
-                    port.cmd.valid.eq(avalon.read | (avalon.write & wdata_fifo.sink.ready)),
-                    port.cmd.last.eq(1),
-                    If(port.cmd.valid & port.cmd.ready,
-                        avalon.waitrequest.eq(0),
-                    )
+            port.cmd.addr.eq(avalon.address - address_offset),
+            port.cmd.we.eq(avalon.write),
+            port.cmd.valid.eq(avalon.read | (avalon.write & wdata_fifo.sink.ready)),
+            port.cmd.last.eq(avalon.burstcount <= 1),
+            If(port.cmd.valid & port.cmd.ready,
+                avalon.waitrequest.eq(0),
+                # If access is a burst, continue it in BURST-ACCESS.
+                If(~port.cmd.last,
+                    NextValue(burst_count,   avalon.burstcount - 1),
+                    NextValue(burst_read,    avalon.read),
+                    NextValue(burst_address, port.cmd.addr + burst_increment),
+                    NextState("BURST-ACCESS")
                 )
             )
         )
-        fsm.act("BURST",
+        fsm.act("BURST-ACCESS",
             avalon.waitrequest.eq(1),
-            port.cmd.addr.eq(address),
+            port.cmd.addr.eq(burst_address),
             port.cmd.we.eq(avalon.write),
-            port.cmd.valid.eq(~burst_write | (avalon.write & wdata_fifo.sink.ready)),
+            port.cmd.valid.eq(burst_read | (avalon.write & wdata_fifo.sink.ready)),
             port.cmd.last.eq(burst_count == 1),
             If(port.cmd.valid & port.cmd.ready,
-                If(burst_write,
-                    avalon.waitrequest.eq(0)
-                ),
+                avalon.waitrequest.eq(~avalon.write),
+                NextValue(burst_count,   burst_count - 1),
+                NextValue(burst_address, burst_address + burst_increment),
                 If(port.cmd.last,
-                    NextState("IDLE")
-                ).Else(
-                    NextValue(burst_count, burst_count - 1),
-                    NextValue(address, address + burst_increment)
+                    NextState("SINGLE-ACCESS")
                 )
             )
         )