From e8a0fc8a5989bbf56d300306f0f32149b238e57f Mon Sep 17 00:00:00 2001
From: Florent Kermarrec <florent@enjoy-digital.fr>
Date: Fri, 23 Feb 2024 10:16:30 +0100
Subject: [PATCH] frontend/dma/LitePCIeDMADescriptorSplitter: Remove FSM.

---
 litepcie/frontend/dma.py | 75 ++++++++++++----------------------------
 1 file changed, 22 insertions(+), 53 deletions(-)

diff --git a/litepcie/frontend/dma.py b/litepcie/frontend/dma.py
index ed8cd11..c137f4e 100644
--- a/litepcie/frontend/dma.py
+++ b/litepcie/frontend/dma.py
@@ -192,64 +192,33 @@ def __init__(self, max_size, address_width):
         # # #
 
         # Signals.
-        # --------
-        length      = Signal(24)
-        length_next = Signal(24)
-
-        # Length/Last Update.
-        # -------------------
-        update_length_last = Signal()
-        self.sync += If(update_length_last,
-            length.eq(length_next),
-            If(length_next > max_size,
-                source.length.eq(max_size),
-                source.last.eq(0),
-            ).Else(
-                source.length.eq(length_next),
-                source.last.eq(1),
-            )
-        )
+        length     = Signal(24)
+        length_rst = Signal()
+        length_inc = Signal()
 
-        # FSM.
-        # ----
-        self.fsm = fsm = FSM(reset_state="IDLE")
-        fsm.act("IDLE",
-            # Set/Clear signals.
-            NextValue(source.first, 1),
-            NextValue(source.address, sink.address),
-            # Update length/last.
-            length_next.eq(length),
-            update_length_last.eq(1),
-            # Wait for a descriptor and go to RUN.
-            If(sink.valid,
-                NextState("RUN")
-            )
-        )
-        fsm.act("RUN",
-            source.valid.eq(1),
-            # When descriptor is accepted...
-            If(source.ready,
-                # Clear first.
-                NextValue(source.first, 0),
-                # Update address.
-                NextValue(source.address, source.address + max_size),
-                # Update length/last.
-                length_next.eq(length - max_size),
-                update_length_last.eq(1),
-                # On last or terminate...
+        # Comb Logic.
+        # -----------
+        self.comb += [
+            source.valid.eq(sink.valid),
+            source.first.eq(length == 0),
+            source.last.eq(sink.length <= (length + max_size)),
+            source.address.eq(sink.address + length),
+            source.irq_disable.eq(sink.irq_disable),
+            source.last_disable.eq(sink.last_disable),
+            If(source.valid & source.ready,
+                length_inc.eq(1),
                 If(source.last | self.terminate,
-                    # Accept Descriptor.
                     sink.ready.eq(1),
-                    # Increment User-ID.
-                    NextValue(source.user_id, source.user_id + 1),
-                    # Return to IDLE..
-                    NextState("IDLE")
+                    length_rst.eq(1),
                 )
             )
-        )
-        self.comb += [
-            source.irq_disable.eq(sink.irq_disable),
-            source.last_disable.eq(sink.last_disable),
+        ]
+
+        # Sync Logic.
+        # -----------
+        self.sync += [
+            If(length_inc, length.eq(length + max_size)),
+            If(length_rst, length.eq(0)),
         ]
 
 # LitePCIeDMAReader --------------------------------------------------------------------------------