dvisampler/dma: buffer full memory words

diff --git a/milkymist/dvisampler/dma.py b/milkymist/dvisampler/dma.py
index 48442bfe573dc1f8791ec8a1d950e149b163eda6..79374b2b46def6dff4d9488434eab09d867a8d0f 100644 (file)
--- a/milkymist/dvisampler/dma.py
+++ b/milkymist/dvisampler/dma.py
@@ -3,6 +3,7 @@ from migen.genlib.fsm import FSM
 from migen.bank.description import *
 from migen.bank.eventmanager import *
 from migen.flow.actor import *
+from migen.genlib.fifo import SyncFIFO
 from migen.actorlib import dma_lasmi
 
 from milkymist.dvisampler.common import frame_layout
@@ -54,6 +55,27 @@ class _SlotArray(Module, AutoCSR):
                ]
                self.comb += [slot.address_done.eq(self.address_done & (current_slot == n)) for n, slot in enumerate(slots)]
 
+class _BufferedWriter(Module):
+       def __init__(self, lasmim, depth=4):
+               self.address_data = Sink([("a", lasmim.aw), ("d", lasmim.dw)])
+               self.busy = Signal()
+
+               ###
+
+               self.submodules.writer = dma_lasmi.Writer(lasmim)
+               self.submodules.fifo = SyncFIFO(lasmim.aw + lasmim.dw, depth)
+               self.comb += [
+                       self.fifo.din.eq(self.address_data.payload.raw_bits()),
+                       self.fifo.we.eq(self.address_data.stb),
+                       self.address_data.ack.eq(self.fifo.writable),
+
+                       self.writer.address_data.payload.raw_bits().eq(self.fifo.dout),
+                       self.fifo.re.eq(self.writer.address_data.ack),
+                       self.writer.address_data.stb.eq(self.fifo.readable),
+                       
+                       self.busy.eq(self.writer.busy | self.fifo.readable)
+               ]
+
 class DMA(Module):
        def __init__(self, lasmim, nslots):
                bus_aw = lasmim.aw
@@ -112,7 +134,7 @@ class DMA(Module):
                        )
 
                # bus accessor
-               self.submodules._bus_accessor = dma_lasmi.Writer(lasmim)
+               self.submodules._bus_accessor = _BufferedWriter(lasmim)
                self.comb += [
                        self._bus_accessor.address_data.payload.a.eq(current_address),
                        self._bus_accessor.address_data.payload.d.eq(cur_memory_word)