from migen.fhdl.std import * from migen.genlib.cdc import NoRetiming, MultiReg, GrayCounter def _inc(signal, modulo): if modulo == 2**flen(signal): return signal.eq(signal + 1) else: return If(signal == (modulo - 1), signal.eq(0) ).Else( signal.eq(signal + 1) ) class _FIFOInterface: def __init__(self, width, depth): self.din = Signal(width) self.we = Signal() self.writable = Signal() # not full self.dout = Signal(width) self.re = Signal() self.readable = Signal() # not empty class SyncFIFO(Module, _FIFOInterface): def __init__(self, width, depth): _FIFOInterface.__init__(self, width, depth) ### do_write = Signal() do_read = Signal() self.comb += [ do_write.eq(self.writable & self.we), do_read.eq(self.readable & self.re) ] level = Signal(max=depth+1) produce = Signal(max=depth) consume = Signal(max=depth) storage = Memory(width, depth) self.specials += storage wrport = storage.get_port(write_capable=True) self.specials += wrport self.comb += [ wrport.adr.eq(produce), wrport.dat_w.eq(self.din), wrport.we.eq(do_write) ] self.sync += If(do_write, _inc(produce, depth)) rdport = storage.get_port(async_read=True) self.specials += rdport self.comb += [ rdport.adr.eq(consume), self.dout.eq(rdport.dat_r) ] self.sync += If(do_read, _inc(consume, depth)) self.sync += [ If(do_write, If(~do_read, level.eq(level + 1)) ).Elif(do_read, level.eq(level - 1) ) ] self.comb += [ self.writable.eq(level != depth), self.readable.eq(level != 0) ] class AsyncFIFO(Module, _FIFOInterface): def __init__(self, width, depth): _FIFOInterface.__init__(self, width, depth) ### depth_bits = log2_int(depth, True) produce = GrayCounter(depth_bits+1) self.add_submodule(produce, "write") consume = GrayCounter(depth_bits+1) self.add_submodule(consume, "read") self.comb += [ produce.ce.eq(self.writable & self.we), consume.ce.eq(self.readable & self.re) ] produce_rdomain = Signal(depth_bits+1) self.specials += [ NoRetiming(produce.q), MultiReg(produce.q, produce_rdomain, "read") ] consume_wdomain = Signal(depth_bits+1) self.specials += [ NoRetiming(consume.q), MultiReg(consume.q, consume_wdomain, "write") ] self.comb += [ self.writable.eq((produce.q[-1] == consume_wdomain[-1]) | (produce.q[-2] == consume_wdomain[-2]) | (produce.q[:-2] != consume_wdomain[:-2])), self.readable.eq(consume.q != produce_rdomain) ] storage = Memory(width, depth) self.specials += storage wrport = storage.get_port(write_capable=True, clock_domain="write") self.specials += wrport self.comb += [ wrport.adr.eq(produce.q_binary[:-1]), wrport.dat_w.eq(self.din), wrport.we.eq(produce.ce) ] rdport = storage.get_port(clock_domain="read") self.specials += rdport self.comb += [ rdport.adr.eq(consume.q_binary[:-1]), self.dout.eq(rdport.dat_r) ]