litex/migen/bus/wishbone.py

from migen.fhdl.structure import *
from migen.corelogic import roundrobin
from migen.corelogic.misc import multimux, optree
from migen.bus.simple import Simple, get_sig_name

_desc = [
	(True,	"adr",	30),
	(True,	"dat",	32),
	(False,	"dat",	32),
	(True,	"sel",	4),
	(True,	"cyc",	1),
	(True,	"stb",	1),
	(False,	"ack",	1),
	(True,	"we",	1),
	(True,	"cti",	3),
	(True,	"bte",	2),
	(False,	"err",	1)
]

class Master(Simple):
	def __init__(self, name=""):
		Simple.__init__(self, _desc, False, name)

class Slave(Simple):
	def __init__(self, name=""):
		Simple.__init__(self, _desc, True, name)

class Arbiter:
	def __init__(self, masters, target):
		self.masters = masters
		self.target = target
		self.rr = roundrobin.RoundRobin(len(self.masters))

	def get_fragment(self):
		comb = []
		
		# mux master->slave signals
		m2s_names = [get_sig_name(x, False) for x in _desc if x[0]]
		m2s_masters = [[getattr(m, name) for name in m2s_names] for m in self.masters]
		m2s_target = [getattr(self.target, name) for name in m2s_names]
		comb += multimux(self.rr.grant, m2s_masters, m2s_target)
		
		# connect slave->master signals
		s2m_names = [get_sig_name(x, False) for x in _desc if not x[0]]
		for name in s2m_names:
			source = getattr(self.target, name)
			i = 0
			for m in self.masters:
				dest = getattr(m, name)
				if name == "ack_i" or name == "err_i":
					comb.append(dest.eq(source & (self.rr.grant == Constant(i, self.rr.grant.bv))))
				else:
					comb.append(dest.eq(source))
				i += 1
		
		# connect bus requests to round-robin selector
		reqs = [m.cyc_o for m in self.masters]
		comb.append(self.rr.request.eq(Cat(*reqs)))
		
		return Fragment(comb) + self.rr.get_fragment()

class Decoder:
	# slaves is a list of pairs:
	# 0) structure.Constant defining address (always decoded on the upper bits)
	#    Slaves can have differing numbers of address bits, but addresses 
	#    must not conflict.
	# 1) wishbone.Slave reference
	# Addresses are decoded from bit 31-offset and downwards.
	# register adds flip-flops after the address comparators. Improves timing,
	# but breaks Wishbone combinatorial feedback.
	def __init__(self, master, slaves, offset=0, register=False):
		self.master = master
		self.slaves = slaves
		self.offset = offset
		self.register = register
		
		addresses = [slave[0] for slave in self.slaves]
		maxbits = max([bits_for(addr) for addr in addresses])
		def mkconst(x):
			if isinstance(x, int):
				return Constant(x, BV(maxbits))
			else:
				return x
		self.addresses = list(map(mkconst, addresses))

	def get_fragment(self):
		comb = []
		sync = []
		
		ns = len(self.slaves)
		slave_sel = Signal(BV(ns))
		slave_sel_r = Signal(BV(ns))
		
		# decode slave addresses
		i = 0
		hi = self.master.adr_o.bv.width - self.offset
		for addr in self.addresses:
			comb.append(slave_sel[i].eq(
				self.master.adr_o[hi-addr.bv.width:hi] == addr))
			i += 1
		if self.register:
			sync.append(slave_sel_r.eq(slave_sel))
		else:
			comb.append(slave_sel_r.eq(slave_sel))
		
		# connect master->slaves signals except cyc
		m2s_names = [(get_sig_name(x, False), get_sig_name(x, True))
			for x in _desc if x[0] and x[1] != "cyc"]
		comb += [getattr(slave[1], name[1]).eq(getattr(self.master, name[0]))
			for name in m2s_names for slave in self.slaves]
		
		# combine cyc with slave selection signals
		i = 0
		for slave in self.slaves:
			comb.append(slave[1].cyc_i.eq(self.master.cyc_o & slave_sel[i]))
			i += 1
		
		# generate master ack (resp. err) by ORing all slave acks (resp. errs)
		comb.append(self.master.ack_i.eq(optree('|', [slave[1].ack_o for slave in self.slaves])))
		comb.append(self.master.err_i.eq(optree('|', [slave[1].err_o for slave in self.slaves])))
		
		# mux (1-hot) slave data return
		masked = [Replicate(slave_sel_r[i], self.master.dat_i.bv.width) & self.slaves[i][1].dat_o for i in range(len(self.slaves))]
		comb.append(self.master.dat_i.eq(optree('|', masked)))
		
		return Fragment(comb, sync)

class InterconnectShared:
	def __init__(self, masters, slaves, offset=0, register=False):
		self._shared = Master("shr")
		self._arbiter = Arbiter(masters, self._shared)
		self._decoder = Decoder(self._shared, slaves, offset, register)
		self.addresses = self._decoder.addresses
	
	def get_fragment(self):
		return self._arbiter.get_fragment() + self._decoder.get_fragment()