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gateware/stereopair_extractor.py

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+from amaranth          import *
+from amaranth.build    import Platform
+from amaranth.lib.fifo import SyncFIFOBuffered
+from amlib.stream import StreamInterface, connect_fifo_to_stream
+
+class StereoPairExtractor(Elaboratable):
+    def __init__(self, max_no_channels: int, fifo_depth):
+        self._channel_bits    = Shape.cast(range(max_no_channels)).width
+        self._fifo_depth      = fifo_depth
+
+        # I/O
+        self.channel_stream_in   = StreamInterface(name="channel_stream_in", payload_width=24, extra_fields=[("channel_nr", self._channel_bits)])
+        self.selected_channel_in = Signal(range(max_no_channels))
+        # the first=left and last=right signals mark the channel on the output stream
+        self.channel_stream_out  = StreamInterface(name="channel_stream_out", payload_width=24)
+        self.level = Signal(range(fifo_depth))
+
+    def elaborate(self, platform: Platform) -> Module:
+        m = Module()
+
+        m.submodules.fifo = fifo = SyncFIFOBuffered(width=24+1, depth=self._fifo_depth)
+
+        in_channel_nr  = self.channel_stream_in.channel_nr
+        out_channel_nr = Signal(self._channel_bits)
+
+        # the ready signal is not wired in the input stream because this
+        # module must not exert upstream back pressure
+        with m.If(  self.channel_stream_in.valid
+                  & (  (in_channel_nr == self.selected_channel_in)
+                     | (in_channel_nr == (self.selected_channel_in + 1)))):
+
+            m.d.comb += [
+                fifo.w_data.eq(Cat(self.channel_stream_in.payload, out_channel_nr[0])),
+                fifo.w_en.eq(1)
+            ]
+
+        m.d.comb += [
+            self.level.eq(fifo.r_level),
+            out_channel_nr.eq(in_channel_nr - self.selected_channel_in),
+            *connect_fifo_to_stream(fifo, self.channel_stream_out),
+            self.channel_stream_out.first.eq(~fifo.r_data[-1]),
+            self.channel_stream_out.last.eq(fifo.r_data[-1]),
+        ]
+
+        return m