litex/migen/bus/asmibus.py

from migen.fhdl.structure import *

class FinalizeError(Exception):
	pass

(SLOT_EMPTY, SLOT_PENDING, SLOT_PROCESSING) = range(3)

class Slot:
	def __init__(self, aw, time):
		self.state = Signal(BV(2))
		self.we = Signal()
		self.adr = Signal(BV(aw))
		self.time = time
		if self.time:
			self._counter = Signal(BV(bits_for(time)))
			self.mature = Signal()
		
		self.allocate = Signal()
		self.allocate_we = Signal()
		self.allocate_adr = Signal(BV(aw))
		self.process = Signal()
		self.call = Signal()
	
	def get_fragment(self):
		comb = []
		sync = [
			If(self.allocate,
				self.state.eq(SLOT_PENDING)
				self.we.eq(self.allocate_we),
				self.adr.eq(self.allocate_adr)
			),
			If(self.process, self.state.eq(SLOT_PROCESSING)),
			If(self.call, self.state.eq(SLOT_EMPTY))
		]
		if self.time:
			comb += [
				self.mature.eq(self._counter == 0)
			]
			sync += [
				If(self.allocate,
					self._counter.eq(self.time)
				).Elif(self._counter.eq != 0,
					self._counter.eq(self._counter - 1)
				)
			]
		return Fragment(comb, sync)

class Port:
	def __init__(self, hub, nslots):
		self.hub = hub
		self.slots = [Slot(self.hub.aw, self.hub.time) for i in range(nslots)]
		self.finalized = False
		
		# request issuance
		self.adr = Signal(BV(self.hub.aw))
		self.we = Signal()
		self.stb = Signal()
		# tag_issue is created by finalize()
		self.ack = Signal()
		
		# request completion
		self.call = Signal()
		# tag_call is created by finalize()
		self.dat_r = Signal(BV(self.hub.dw))
		self.dat_w = Signal(BV(self.hub.dw))
		self.dat_wm = Signal(BV(self.hub.dw//8))
	
	def finalize(self, tagbits, base):
		if self.finalized:
			raise FinalizeError
		self.tagbits = tagbits
		self.base = base
		nslots = len(self.slots)
		if nslots > 1:
			self.tag_issue = Signal(BV(bits_for(nslots-1)))
		self.tag_call = Signal(BV(tagbits))
	
	def get_call_expression(self, slotn=0):
		if not self.finalized:
			raise FinalizeError
		return self.call \
			&& (self.tag_call == Constant(self.base + slotn, BV(self.tagbits)))
		
	def get_fragment(self):
		if not self.finalized:
			raise FinalizeError
		
		slots_fragment = sum([s.get_fragment() for s in self.slots], Fragment())
		
		comb = []
		sync = []
		
		# allocate
		for s in self.slots:
			comb += [
				s.allocate_we.eq(self.we),
				s.allocate_adr.eq(self.adr)
			]
		choose_slot = None
		for s in reversed(self.slots):
			choose_slot = If(s.state == SLOT_EMPTY,
				self.ack.eq(1),
				s.allocate.eq(self.stb)
			).Else(choose_slot)
		comb.append(choose_slot)
		
		# call
		comb += [s.call.eq(self.get_call_expression(n))
			for n, s in enumerate(self.slots)]
		
		return slots_fragment + Fragment(comb, sync)

class Hub:
	def __init__(self, aw, dw, time=0):
		self.aw = aw
		self.dw = dw
		self.time = time
		self.ports = []
		self.finalized = False
	
	def get_port(self, nslots=1):
		if self.finalized:
			raise FinalizeError
		self.ports.append(Port(self, nslots))
	
	def finalize(self):
		if self.finalized:
			raise FinalizeError
		self.finalized = True
		nslots = sum([len(port.slots) for port in self.ports])
		tagbits = bits_for(nslots-1)
		base = 0
		for port in self.ports:
			port.finalize(tagbits, base)
			base += len(port.slots)
	
	def get_fragment(self):
		if not self.finalized:
			raise FinalizeError
		return sum([port.get_fragment() for port in self.ports])