litex/milkymist/asmicon/multiplexer.py

from migen.fhdl.structure import *
from migen.fhdl.module import Module
from migen.genlib.roundrobin import *
from migen.genlib.misc import optree
from migen.genlib.fsm import FSM

class CommandRequest:
	def __init__(self, a, ba):
		self.a = Signal(a)
		self.ba = Signal(ba)
		self.cas_n = Signal(reset=1)
		self.ras_n = Signal(reset=1)
		self.we_n = Signal(reset=1)

class CommandRequestRW(CommandRequest):
	def __init__(self, a, ba, tagbits):
		CommandRequest.__init__(self, a, ba)
		self.stb = Signal()
		self.ack = Signal()
		self.is_read = Signal()
		self.is_write = Signal()
		self.tag = Signal(tagbits)

class _CommandChooser(Module):
	def __init__(self, requests, tagbits):
		self.want_reads = Signal()
		self.want_writes = Signal()
		# NB: cas_n/ras_n/we_n are 1 when stb is inactive
		self.cmd = CommandRequestRW(len(requests[0].a), len(requests[0].ba), tagbits)
	
		###

		rr = RoundRobin(len(requests), SP_CE)
		self.submodules += rr
		
		self.comb += [rr.request[i].eq(req.stb & ((req.is_read == self.want_reads) | (req.is_write == self.want_writes)))
			for i, req in enumerate(requests)]
		
		stb = Signal()
		self.comb += stb.eq(Array(req.stb for req in requests)[rr.grant])
		for name in ["a", "ba", "is_read", "is_write", "tag"]:
			choices = Array(getattr(req, name) for req in requests)
			self.comb += getattr(self.cmd, name).eq(choices[rr.grant])
		for name in ["cas_n", "ras_n", "we_n"]:
			# we should only assert those signals when stb is 1
			choices = Array(getattr(req, name) for req in requests)
			self.comb += If(self.cmd.stb, getattr(self.cmd, name).eq(choices[rr.grant]))
		self.comb += self.cmd.stb.eq(stb \
			& (self.cmd.is_read == self.want_reads) \
			& (self.cmd.is_write == self.want_writes))
		
		self.comb += [If(self.cmd.stb & self.cmd.ack & (rr.grant == i), req.ack.eq(1))
			for i, req in enumerate(requests)]
		self.comb += rr.ce.eq(self.cmd.ack)

class _Steerer(Module):
	def __init__(self, commands, dfi):
		ncmd = len(commands)
		nph = len(dfi.phases)
		self.sel = [Signal(max=ncmd) for i in range(nph)]
	
		###
	
		def stb_and(cmd, attr):
			if not hasattr(cmd, "stb"):
				return 0
			else:
				return cmd.stb & getattr(cmd, attr)
		for phase, sel in zip(dfi.phases, self.sel):
			self.comb += [
				phase.cke.eq(1),
				phase.cs_n.eq(0)
			]
			self.sync += [
				phase.address.eq(Array(cmd.a for cmd in commands)[sel]),
				phase.bank.eq(Array(cmd.ba for cmd in commands)[sel]),
				phase.cas_n.eq(Array(cmd.cas_n for cmd in commands)[sel]),
				phase.ras_n.eq(Array(cmd.ras_n for cmd in commands)[sel]),
				phase.we_n.eq(Array(cmd.we_n for cmd in commands)[sel]),
				phase.rddata_en.eq(Array(stb_and(cmd, "is_read") for cmd in commands)[sel]),
				phase.wrdata_en.eq(Array(stb_and(cmd, "is_write") for cmd in commands)[sel])
			]

class _Datapath(Module):
	def __init__(self, timing_settings, command, dfi, hub):
		tagbits = len(hub.tag_call)
		
		rd_valid = Signal()
		rd_tag = Signal(tagbits)
		wr_valid = Signal()
		wr_tag = Signal(tagbits)
		self.comb += [
			hub.call.eq(rd_valid | wr_valid),
			If(wr_valid,
				hub.tag_call.eq(wr_tag)
			).Else(
				hub.tag_call.eq(rd_tag)
			)
		]
		
		rd_delay = timing_settings.rd_delay + 1
		rd_valid_d = [Signal() for i in range(rd_delay)]
		rd_tag_d = [Signal(tagbits) for i in range(rd_delay)]
		for i in range(rd_delay):
			if i:
				self.sync += [
					rd_valid_d[i].eq(rd_valid_d[i-1]),
					rd_tag_d[i].eq(rd_tag_d[i-1])
				]
			else:
				self.sync += [
					rd_valid_d[i].eq(command.stb & command.ack & command.is_read),
					rd_tag_d[i].eq(command.tag)
				]		
		self.comb += [
			rd_valid.eq(rd_valid_d[-1]),
			rd_tag.eq(rd_tag_d[-1]),
			wr_valid.eq(command.stb & command.ack & command.is_write),
			wr_tag.eq(command.tag),
		]
		
		all_rddata = [p.rddata for p in dfi.phases]
		all_wrdata = [p.wrdata for p in dfi.phases]
		all_wrdata_mask = [p.wrdata_mask for p in dfi.phases]
		self.comb += [
			hub.dat_r.eq(Cat(*all_rddata)),
			Cat(*all_wrdata).eq(hub.dat_w),
			Cat(*all_wrdata_mask).eq(hub.dat_wm)
		]

class Multiplexer(Module):
	def __init__(self, phy_settings, geom_settings, timing_settings, bank_machines, refresher, dfi, hub):
		assert(phy_settings.nphases == len(dfi.phases))
		if phy_settings.nphases != 2:
			raise NotImplementedError("TODO: multiplexer only supports 2 phases")
	
		# Command choosing
		requests = [bm.cmd for bm in bank_machines]
		tagbits = len(hub.tag_call)
		choose_cmd = _CommandChooser(requests, tagbits)
		choose_req = _CommandChooser(requests, tagbits)
		self.comb += [
			choose_cmd.want_reads.eq(0),
			choose_cmd.want_writes.eq(0)
		]
		self.submodules += choose_cmd, choose_req
		
		# Command steering
		nop = CommandRequest(geom_settings.mux_a, geom_settings.bank_a)
		commands = [nop, choose_cmd.cmd, choose_req.cmd, refresher.cmd] # nop must be 1st
		(STEER_NOP, STEER_CMD, STEER_REQ, STEER_REFRESH) = range(4)
		steerer = _Steerer(commands, dfi)
		self.submodules += steerer
		
		# Read/write turnaround
		read_available = Signal()
		write_available = Signal()
		self.comb += [
			read_available.eq(optree("|", [req.stb & req.is_read for req in requests])),
			write_available.eq(optree("|", [req.stb & req.is_write for req in requests]))
		]
		
		def anti_starvation(timeout):
			en = Signal()
			max_time = Signal()
			if timeout:
				t = timeout - 1
				time = Signal(max=t+1)
				self.comb += max_time.eq(time == 0)
				self.sync += If(~en,
						time.eq(t)
					).Elif(~max_time,
						time.eq(time - 1)
					)
			else:
				self.comb += max_time.eq(0)
			return en, max_time
		read_time_en, max_read_time = anti_starvation(timing_settings.read_time)
		write_time_en, max_write_time = anti_starvation(timing_settings.write_time)
		
		# Refresh
		self.comb += [bm.refresh_req.eq(refresher.req) for bm in bank_machines]
		go_to_refresh = Signal()
		self.comb += go_to_refresh.eq(optree("&", [bm.refresh_gnt for bm in bank_machines]))
		
		# Datapath
		datapath = _Datapath(timing_settings, choose_req.cmd, dfi, hub)
		self.submodules += datapath
		
		# Control FSM
		fsm = FSM("READ", "WRITE", "REFRESH", delayed_enters=[
			("RTW", "WRITE", timing_settings.rd_delay),
			("WTR", "READ", timing_settings.tWR)
		])
		self.submodules += fsm
		fsm.act(fsm.READ,
			read_time_en.eq(1),
			choose_req.want_reads.eq(1),
			choose_cmd.cmd.ack.eq(1),
			choose_req.cmd.ack.eq(1),
			steerer.sel[1-phy_settings.rdphase].eq(STEER_CMD),
			steerer.sel[phy_settings.rdphase].eq(STEER_REQ),
			If(write_available,
				# TODO: switch only after several cycles of ~read_available?
				If(~read_available | max_read_time, fsm.next_state(fsm.RTW))
			),
			If(go_to_refresh, fsm.next_state(fsm.REFRESH))
		)
		fsm.act(fsm.WRITE,
			write_time_en.eq(1),
			choose_req.want_writes.eq(1),
			choose_cmd.cmd.ack.eq(1),
			choose_req.cmd.ack.eq(1),
			steerer.sel[1-phy_settings.wrphase].eq(STEER_CMD),
			steerer.sel[phy_settings.wrphase].eq(STEER_REQ),
			If(read_available,
				If(~write_available | max_write_time, fsm.next_state(fsm.WTR))
			),
			If(go_to_refresh, fsm.next_state(fsm.REFRESH))
		)
		fsm.act(fsm.REFRESH,
			steerer.sel[0].eq(STEER_REFRESH),
			If(~refresher.req, fsm.next_state(fsm.READ))
		)
		# FIXME: workaround for zero-delay loop simulation problem with Icarus Verilog
		self.comb += refresher.ack.eq(fsm._state == fsm.REFRESH)