soc/core: add frequency meter

litex/soc/cores/frequency_meter.py

@@ -0,0 +1,67 @@
+from litex.gen import *
+from litex.gen.genlib.cdc import MultiReg, GrayCounter
+from litex.gen.genlib.cdc import GrayDecoder
+
+from litex.soc.interconnect.csr import *
+
+
+class Sampler(Module):
+    def __init__(self, width):
+        self.latch = Signal()
+        self.i = Signal(width)
+        self.o = Signal(32)
+
+        # # #
+
+        inc = Signal(width)
+        counter = Signal(32)
+
+        # use wrapping property of unsigned arithmeric to reset the counter
+        # each cycle (reseting fmeter clock domain is unreliable)
+        i_d = Signal(width)
+        self.sync += i_d.eq(self.i)
+        self.comb += inc.eq(self.i - i_d)
+
+        self.sync += \
+            If(self.latch,
+                counter.eq(0),
+                self.o.eq(counter),
+            ).Else(
+                counter.eq(counter + inc)
+            )
+
+
+class FrequencyMeter(Module, AutoCSR):
+    def __init__(self, period, width=6):
+        self.clk = Signal()
+        self.value = CSRStatus(32)
+
+        # # #
+
+        self.clock_domains.cd_fmeter = ClockDomain(reset_less=True)
+        self.comb += self.cd_fmeter.clk.eq(self.clk)
+
+        # period generation
+        period_done = Signal()
+        period_counter = Signal(32)
+        self.comb += period_done.eq(period_counter == period)
+        self.sync += \
+            If(period_done,
+                period_counter.eq(0),
+            ).Else(
+                period_counter.eq(period_counter + 1)
+            )
+
+        # frequency measurement
+        event_counter = ClockDomainsRenamer("fmeter")(GrayCounter(width))
+        gray_decoder = GrayDecoder(width)
+        sampler = Sampler(width)
+        self.submodules += event_counter, gray_decoder, sampler
+
+        self.specials += MultiReg(event_counter.q, gray_decoder.i)
+        self.comb += [
+            event_counter.ce.eq(1),
+            sampler.latch.eq(period_done),
+            sampler.i.eq(gray_decoder.o),
+            self.value.status.eq(sampler.o)
+        ]