From 9ce2f67bb170352d87db1f0a88d145c658f0c293 Mon Sep 17 00:00:00 2001
From: Florent Kermarrec <florent@enjoy-digital.fr>
Date: Fri, 23 Jun 2017 22:00:49 +0200
Subject: [PATCH] frontend: add dram fifo (untested)

---
 litedram/frontend/fifo.py | 139 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 139 insertions(+)
 create mode 100644 litedram/frontend/fifo.py

diff --git a/litedram/frontend/fifo.py b/litedram/frontend/fifo.py
new file mode 100644
index 0000000..a82a726
--- /dev/null
+++ b/litedram/frontend/fifo.py
@@ -0,0 +1,139 @@
+from litex.gen import *
+
+from litex.soc.interconnect import stream
+
+from litedram.frontend import dma
+
+
+def _inc(signal, modulo):
+    if modulo == 2**len(signal):
+        return signal.eq(signal + 1)
+    else:
+        return If(signal == (modulo - 1),
+            signal.eq(0)
+        ).Else(
+            signal.eq(signal + 1)
+        )
+
+
+def _raw_layout(endpoint):
+    raw_layout = []
+    raw_layout.append(endpoint.first)
+    raw_layout.append(endpoint.last)
+    raw_layout.append(endpoint.payload.raw_bits())
+    return Cat(iter(raw_layout))
+
+
+class _LiteDRAMFIFOCtrl(Module):
+    def __init__(self, base, depth):
+        self.base = base
+        self.depth = depth
+        self.level = Signal(max=depth+1)
+
+        # # #
+
+        # to buffer write
+        self.writable = Signal()
+        self.write_address = Signal(max=depth)
+
+        # from buffer write
+        self.write = Signal()
+
+        # to buffer read
+        self.readable = Signal()
+        self.read_address = Signal(max=depth)
+
+        # from buffer read
+        self.read = Signal()
+
+        # # #
+
+        produce = self.write_address
+        consume = self.read_address
+
+        self.sync += [
+            If(self.write,
+                _inc(produce, depth)
+            ),
+            If(self.read,
+                _inc(consume, depth)
+            ),
+            If(self.write & ~self.read,
+                self.level.eq(self.level + 1),
+            ).Elif(self.read & ~self.write,
+                self.level.eq(self.level - 1)
+            )
+        ]
+
+        self.comb += [
+            self.writable.eq(self.level != depth),
+            self.readable.eq(self.level != 0)
+        ]
+
+
+class _LiteDRAMFIFOWriter(Module):
+    def __init__(self, ctrl, layout, port):
+        self.sink = sink = stream.Endpoint(layout)
+
+        # # #
+
+        writer = dma.LiteDRAMDMAWriter(port)
+        self.submodules += writer
+
+        self.submodules.fsm = fsm = FSM(reset_state="IDLE")
+        fsm.act("IDLE",
+            If(ctrl.writable & sink.valid,
+                NextState("WRITE")
+            )
+        )
+        fsm.act("WRITE",
+            writer.sink.valid.eq(1),
+            If(writer.sink.ready,
+                ctrl.write.eq(1),
+                sink.ready.eq(1),
+                NextState("IDLE")
+            )
+        )
+        self.comb += [
+            writer.sink.address.eq(ctrl.write_address + ctrl.base//(port.dw//8)),
+            writer.sink.data.eq(_raw_layout(sink))
+        ]
+
+
+class _LiteDRAMFIFOReader(Module):
+    def __init__(self, ctrl, layout, port):
+        self.source = source = stream.Endpoint(layout)
+
+        # # #
+
+        reader = dma.LiteDRAMDMAReader(port)
+        self.submodules += reader
+
+        self.submodules.fsm = fsm = FSM(reset_state="IDLE")
+        fsm.act("IDLE",
+            If(ctrl.readable,
+                NextState("READ")
+            )
+        )
+        fsm.act("READ",
+            reader.sink.valid.eq(1),
+            If(reader.sink.ready,
+                ctrl.read.eq(1),
+                NextState("IDLE")
+            )
+        )
+
+        self.comb += [
+            reader.sink.address.eq(ctrl.read_address + ctrl.base//(port.dw//8)),
+            source.valid.eq(reader.source.valid),
+            _raw_layout(source).eq(reader.source.data),
+            reader.source.ready.eq(source.ready)
+        ]
+
+
+class LiteDRAMFIFO(Module):
+    def __init__(self, layout, base, depth, write_port, read_port):
+        self.submodules.ctrl = _LiteDRAMFIFOCtrl(base, depth)
+        self.submodules.writer = _LiteDRAMFIFOWriter(self.ctrl, layout, write_port)
+        self.submodules.reader = _LiteDRAMFIFOReader(self.ctrl, layout, read_port)
+        self.sink, self.source = self.writer.sink, self.reader.source