def elaborate(self, _: Platform) -> Module:
"""Implements the logic of a transparent latch."""
m = Module()
internal_reg = Signal(self.size, reset=0, reset_less=True)
# Local clock domain so we can clock data into the
# internal memory on the negative edge of le.
le_clk = ClockDomain("le_clk", clk_edge="neg", local=True)
m.domains.le_clk = le_clk
le_clk.clk = self.le
m.d.le_clk += internal_reg.eq(self.data_in)
m.d.comb += self.data_out.eq(Mux(self.n_oe, 0, internal_reg))
with m.If(self.le & ~self.n_oe):
m.d.comb += self.data_out.eq(self.data_in)
return m
def elaborate(self, _: Platform) -> Module:
"""Implements the logic of an asynchronous memory.
Essentially implements the wr-controlled write cycle, where
the oe signal doesn't matter. We can't really implement the
delays involved, so be safe with your signals :)
"""
m = Module()
# Local clock domain so we can clock data into the memory
# on the positive edge of n_wr.
wr_clk = ClockDomain("wr_clk", local=True)
m.domains.wr_clk = wr_clk
wr_clk.clk = self.n_wr
m.d.comb += self.data_out.eq(0)
with m.If(~self.n_oe & self.n_wr):
m.d.comb += self.data_out.eq(self._mem[self.addr])
m.d.wr_clk += self._mem[self.addr].eq(self.data_in)
return m
def formal(cls) -> Tuple[Module, List[Signal]]:
"""Formal verification for the async memory.
Note that you MUST have multiclock on in the sby file, because there is
more than one clock in the system -- the default formal clock and the
local clock inside the memory.
"""
m = Module()
m.submodules.mem = mem = AsyncMemory(width=32, addr_lines=5)
# Assume "good practices":
# * n_oe and n_wr are never simultaneously 0, and any changes
# are separated by at least a cycle to allow buffers to turn off.
# * memory address remains stable throughout a write cycle, and
# is also stable just before a write cycle.
m.d.comb += Assume(mem.n_oe | mem.n_wr)
# Paren placement is very important! While Python logical operators
# and, or have lower precedence than ==, the bitwise operators
# &, |, ^ have *higher* precedence. It can be confusing when it looks
# like you're writing a boolean expression, but you're actually writing
# a bitwise expression.
with m.If(Fell(mem.n_oe)):
m.d.comb += Assume((mem.n_wr == 1) & (Past(mem.n_wr) == 1))
with m.If(Fell(mem.n_wr)):
m.d.comb += Assume((mem.n_oe == 1) & (Past(mem.n_oe) == 1))
with m.If(Rose(mem.n_wr) | (mem.n_wr == 0)):
m.d.comb += Assume(Stable(mem.addr))
m.d.comb += Cover((mem.data_out == 0xAAAAAAAA)
& (Past(mem.data_out) == 0xBBBBBBBB))
# Make sure that when the output is disabled, the output is zero, and
# when enabled, it's whatever we're pointing at in memory.
with m.If(mem.n_oe == 1):
m.d.comb += Assert(mem.data_out == 0)
with m.Else():
m.d.comb += Assert(mem.data_out == mem._mem[mem.addr])
# If we just wrote data, make sure that cell that we pointed at
# for writing now contains the data we wrote.
with m.If(Rose(mem.n_wr)):
m.d.comb += Assert(mem._mem[Past(mem.addr)] == Past(mem.data_in))
# Pick an address, any address.
check_addr = AnyConst(5)
# We assert that unless that address is written, its data will not
# change. To know when we've written the data, we have to create
# a clock domain to let us save the data when written.
saved_data_clk = ClockDomain("saved_data_clk")
m.domains.saved_data_clk = saved_data_clk
saved_data_clk.clk = mem.n_wr
saved_data = Signal(32)
with m.If(mem.addr == check_addr):
m.d.saved_data_clk += saved_data.eq(mem.data_in)
with m.If(Initial()):
m.d.comb += Assume(saved_data == mem._mem[check_addr])
m.d.comb += Assume(mem.n_wr == 1)
with m.Else():
m.d.comb += Assert(saved_data == mem._mem[check_addr])
return m, [mem.addr, mem.data_in, mem.n_wr, mem.n_oe]
def formal(cls) -> Tuple[Module, List[Signal]]:
"""Formal verification for the register card."""
m = Module()
ph1 = ClockDomain("ph1")
ph2 = ClockDomain("ph2")
regs = RegCard()
m.domains += [ph1, ph2]
m.submodules += regs
# Generate the ph1 and ph2 clocks.
cycle_count = Signal(8, reset=0, reset_less=True)
phase_count = Signal(3, reset=0, reset_less=True)
m.d.sync += phase_count.eq(phase_count + 1)
with m.Switch(phase_count):
with m.Case(0, 1, 2):
m.d.comb += ph1.clk.eq(1)
with m.Default():
m.d.comb += ph1.clk.eq(0)
with m.Switch(phase_count):
with m.Case(1, 4):
m.d.comb += ph2.clk.eq(0)
with m.Default():
m.d.comb += ph2.clk.eq(1)
with m.If(phase_count == 5):
m.d.sync += phase_count.eq(0)
m.d.sync += cycle_count.eq(cycle_count + 1)
# This is how we expect to use the card.
with m.If(phase_count > 0):
m.d.comb += [
Assume(Stable(regs.reg_x)),
Assume(Stable(regs.reg_y)),
Assume(Stable(regs.reg_z)),
Assume(Stable(regs.reg_page)),
Assume(Stable(regs.reg_to_x)),
Assume(Stable(regs.reg_to_y)),
Assume(Stable(regs.data_z)),
]
# Figure out how to get to the point where X and Y are nonzero and different.
m.d.comb += Cover((regs.data_x != 0) & (regs.data_y != 0)
& (regs.data_x != regs.data_y))
# X and Y buses should not change during a cycle, except for the first phase
with m.Switch(phase_count):
with m.Case(2, 3, 4, 5):
with m.If(regs.data_x != 0):
m.d.comb += Assert(Stable(regs.data_x))
with m.If(regs.data_y != 0):
m.d.comb += Assert(Stable(regs.data_y))
# X and Y buses should be zero if there is no data transfer.
with m.If(regs.reg_to_x == 0):
m.d.comb += Assert(regs.data_x == 0)
with m.If(regs.reg_to_y == 0):
m.d.comb += Assert(regs.data_y == 0)
with m.If(phase_count > 0):
# X and Y buses should be zero if we read from register 0.
with m.If(regs.reg_to_x & (regs.reg_x == 0)):
m.d.comb += Assert(regs.data_x == 0)
with m.If(regs.reg_to_y & (regs.reg_y == 0)):
m.d.comb += Assert(regs.data_y == 0)
write_pulse = Signal()
m.d.comb += write_pulse.eq(phase_count != 4)
# On write, the data should have been written to both banks.
past_mem_addr = Signal(6)
m.d.comb += past_mem_addr[:5].eq(Past(regs.reg_z))
m.d.comb += past_mem_addr[5].eq(Past(regs.reg_page))
past_z = Past(regs.data_z)
with m.If(Rose(write_pulse)):
m.d.comb += Assert(regs._x_bank._mem[past_mem_addr] == past_z)
m.d.comb += Assert(regs._y_bank._mem[past_mem_addr] == past_z)
# Pick an register, any register, except 0. We assert that unless
# it is written, its data will not change.
check_addr = AnyConst(5)
check_page = AnyConst(1)
saved_data = Signal(32)
stored_x_data = Signal(32)
stored_y_data = Signal(32)
write_pulse_domain = ClockDomain("write_pulse_domain", local=True)
m.domains.write_pulse_domain = write_pulse_domain
write_pulse_domain.clk = write_pulse
mem_addr = Signal(6)
m.d.comb += Assume(check_addr != 0)
m.d.comb += [
mem_addr[:5].eq(check_addr),
mem_addr[5].eq(check_page),
stored_x_data.eq(regs._x_bank._mem[mem_addr]),
stored_y_data.eq(regs._y_bank._mem[mem_addr]),
]
with m.If((regs.reg_z == check_addr) & (regs.reg_page == check_page)):
m.d.write_pulse_domain += saved_data.eq(regs.data_z)
with m.If(Initial()):
m.d.comb += Assume(saved_data == stored_x_data)
m.d.comb += Assume(stored_x_data == stored_y_data)
with m.Else():
m.d.comb += Assert(saved_data == stored_x_data)
m.d.comb += Assert(saved_data == stored_y_data)
return m, [regs.data_z, regs.reg_to_x, regs.reg_to_y,
regs.reg_x, regs.reg_y, regs.reg_z, regs.reg_page, ph1.clk, ph2.clk, saved_data,
stored_x_data, stored_y_data]