litex/milkymist/timer/__init__.py

from migen.fhdl.structure import *
from migen.fhdl.module import Module
from migen.bank.description import *
from migen.bank.eventmanager import *

class Timer(Module, AutoCSR):
	def __init__(self, width=32):
		self._load = CSRStorage(width)
		self._reload = CSRStorage(width)
		self._en = CSRStorage()
		self._update_value = CSR()
		self._value = CSRStatus(width)
		
		self.submodules.ev = EventManager()
		self.ev.zero = EventSourceProcess()
		self.ev.finalize()

		###

		value = Signal(width)
		self.sync += [
			If(self._en.storage,
				If(value == 0,
					# set reload to 0 to disable reloading
					value.eq(self._reload.storage)
				).Else(
					value.eq(value - 1)
				)
			).Else(
				value.eq(self._load.storage)
			),
			If(self._update_value.re, self._value.status.eq(value))
		]
		self.comb += self.ev.zero.trigger.eq(value != 0)