+ go_now = Signal(reset_less=True) # testing no-delay ALU
+
+ with m.If(self.p_valid_i):
+ # input is valid. next check, if we already said "ready" or not
+ with m.If(~self.p_ready_o):
+ # we didn't say "ready" yet, so say so and initialise
+ m.d.sync += self.p_ready_o.eq(1)
+
+ # as this is a "fake" pipeline, just grab the output right now
+ with m.Switch(self.op):
+ for i, mod in enumerate([add, sub, mul, shf]):
+ with m.Case(i):
+ m.d.sync += self.o.eq(mod.o)
+ with m.If(self.op == 2): # MUL, to take 5 instructions
+ m.d.sync += self.counter.eq(5)
+ with m.Elif(self.op == 3): # SHIFT to take 7
+ m.d.sync += self.counter.eq(7)
+ with m.Elif(self.op == 1): # SUB to take 2
+ m.d.sync += self.counter.eq(2)
+ with m.Else(): # ADD to take 1, straight away
+ m.d.sync += self.counter.eq(1)
+ m.d.comb += go_now.eq(1)
+ with m.Else():
+ # input says no longer valid, so drop ready as well.
+ # a "proper" ALU would have had to sync in the opcode and a/b ops
+ m.d.sync += self.p_ready_o.eq(0)
+
+ # ok so the counter's running: when it gets to 1, fire the output
+ with m.If((self.counter == 1) | go_now):
+ # set the output as valid if the recipient is ready for it
+ m.d.sync += self.n_valid_o.eq(1)
+ with m.If(self.n_ready_i & self.n_valid_o):
+ m.d.sync += self.n_valid_o.eq(0)
+ # recipient said it was ready: reset back to known-good.
+ m.d.sync += self.counter.eq(0) # reset the counter
+ m.d.sync += self.o.eq(0) # clear the output for tidiness sake
+
+ # countdown to 1 (transition from 1 to 0 only on acknowledgement)
+ with m.If(self.counter > 1):
+ m.d.sync += self.counter.eq(self.counter - 1)
+