litex/milkymist/dvisampler/wer.py

from migen.fhdl.std import *
from migen.bank.description import *
from migen.genlib.misc import optree
from migen.genlib.cdc import PulseSynchronizer

from milkymist.dvisampler.common import control_tokens

class WER(Module, AutoCSR):
	def __init__(self, period_bits=24):
		self.data = Signal(10)
		self._r_update = CSR()
		self._r_value = CSRStatus(period_bits)

		###

		# pipeline stage 1
		# we ignore the 10th (inversion) bit, as it is independent of the transition minimization
		data_r = Signal(9)
		self.sync.pix += data_r.eq(self.data[:9])

		# pipeline stage 2
		transitions = Signal(8)
		self.comb += [transitions[i].eq(data_r[i] ^ data_r[i+1]) for i in range(8)]
		transition_count = Signal(max=9)
		self.sync.pix += transition_count.eq(optree("+", [transitions[i] for i in range(8)]))

		is_control = Signal()
		self.sync.pix += is_control.eq(optree("|", [data_r == ct for ct in control_tokens]))

		# pipeline stage 3
		is_error = Signal()
		self.sync.pix += is_error.eq((transition_count > 4) & ~is_control)

		# counter
		period_counter = Signal(period_bits)
		period_done = Signal()
		self.sync.pix += Cat(period_counter, period_done).eq(period_counter + 1)

		wer_counter = Signal(period_bits)
		wer_counter_r = Signal(period_bits)
		wer_counter_r_updated = Signal()
		self.sync.pix += [
			wer_counter_r_updated.eq(period_done),
			If(period_done,
				wer_counter_r.eq(wer_counter),
				wer_counter.eq(0)
			).Elif(is_error,
				wer_counter.eq(wer_counter + 1)
			)
		]

		# sync to system clock domain
		wer_counter_sys = Signal(period_bits)
		self.submodules.ps_counter = PulseSynchronizer("pix", "sys")
		self.comb += self.ps_counter.i.eq(wer_counter_r_updated)
		self.sync += If(self.ps_counter.o, wer_counter_sys.eq(wer_counter_r))

		# register interface
		self.sync += If(self._r_update.re, self._r_value.status.eq(wer_counter_sys))