sram: redesigned write FSM. removed unused signals

src/gateware/aux_controller.py

@@ -21,7 +21,6 @@ class SRAM(Module):
             bus = axi.Interface()
         self.bus = bus
         bus_data_width = len(self.bus.r.data)
-        bus_addr_width = len(self.bus.ar.addr)
         if isinstance(mem_or_size, Memory):
             assert(mem_or_size.width <= bus_data_width)
             self.mem = mem_or_size
@@ -34,21 +33,21 @@ class SRAM(Module):
 
         ###
 
-        # Dout : Data received from CPU, output by SRAM <- port.dat_r
-        # Din : Data driven into SRAM, written into CPU <- port.dat_w
-        self.dout_index = Signal(bus_addr_width)  # is this legal?
-        self.din_index = Signal(bus_addr_width)
-        self.din_ready = Signal()
-        self.dout = Signal(64)
-        self.din = Signal(64)
-
         ar, aw, w, r, b = attrgetter("ar", "aw", "w", "r", "b")(bus)
 
+        # Dout : Data received from CPU, output by SRAM <- port.dat_r
+        # Din : Data driven into SRAM, written into CPU <- port.dat_w
+        self.dout_index = Signal.like(ar.len)
+
         self.r_addr_incr = axi.Incr(ar)
+        self.w_addr_incr = axi.Incr(aw)
 
         ### Read
 
-        self.comb += r.data.eq(port.dat_r) 
+        self.comb += [
+            r.data.eq(port.dat_r),
+            port.adr.eq(self.r_addr_incr.addr)
+        ]
 
         # read control
         self.submodules.read_fsm = read_fsm = FSM(reset_state="IDLE")
@@ -60,15 +59,12 @@ class SRAM(Module):
             )
         )
         read_fsm.act("READ_START",
-            r.data.eq(port.dat_r),
             r.resp.eq(axi.Response.okay.value),
             r.valid.eq(1),
             If(r.ready,
-                r.data.eq(port.dat_r), # that should be always updated, right?
                 NextState("READ"))
         )
         read_fsm.act("READ",
-            r.data.eq(port.dat_r),
             If(r.last & r.ready, # that's a smart way of skipping "LAST" state    
                 NextState("IDLE")
             )
@@ -79,73 +75,67 @@ class SRAM(Module):
                 self.dout_index.eq(0),
                 r.valid.eq(0),  # shall it be reset too on IDLE?
                 ar.ready.eq(0),
+                r.last.eq(0)
             ).Else(If(r.ready & read_fsm.ongoing("READ"),
                     self.dout_index.eq(self.dout_index+1),
-                    port.adr.eq(self.r_addr_incr.addr),
                     If(self.dout_index==ar.len, r.last.eq(1)) # and update last
                 )
             )
         ]
 
         ### Write
-        self.comb += [
-            port.dat_w.eq(w.data),
-            port.addr.eq(aw.addr),
-            # w.strb.eq(0xff),
-            # aw.burst.eq(axi.Burst.incr.value),
-            # aw.len.eq(IN_BURST_LEN-1), # Number of transfers in burst minus 1
-            # aw.size.eq(3), # Width of burst: 3 = 8 bytes = 64 bits
-            # aw.cache.eq(0xf),
-            # b.ready.eq(1),
-        ]
 
-        self.submodules.write_fsm = write_fsm = FSM(reset_state="IDLE")
-        write_fsm.act("IDLE",
-            w.valid.eq(0),
-            aw.valid.eq(0),
-            If(self.trigger_stb,
-                aw.valid.eq(1),
-                If(aw.ready, # assumes aw.ready is not randomly deasserted
-                    NextState("DATA_WAIT")
-                ).Else(
-                    NextState("AW_READY_WAIT")
+        if not read_only:
+            self.comb += [
+                port.dat_w.eq(w.data),
+                port.addr.eq(self.w_addr_incr.addr),
+            ]
+
+            self.submodules.write_fsm = write_fsm = FSM(reset_state="IDLE")
+            write_fsm.act("IDLE",
+                w.ready.eq(0),
+                aw.ready.eq(0),
+                b.valid.eq(0),
+                If(aw.valid,
+                    NextState("AW_VALID_WAIT")
                 )
             )
-        )
-        write_fsm.act("AW_READY_WAIT",
-            aw.valid.eq(1),
-            If(aw.ready,
-                NextState("DATA_WAIT"),
+            write_fsm.act("AW_VALID_WAIT",  # wait for data
+                aw.ready.eq(1),
+                If(w.valid,
+                    NextState("WRITE"),
+                )
             )
-        )
-        write_fsm.act("DATA_WAIT",
-            aw.valid.eq(0),
-            If(self.din_ready,  # probably unnecessary?
-                w.valid.eq(1),
-                NextState("WRITE")
+            # write_fsm.act("DATA_WAIT",
+            #     aw.valid.eq(0),
+            #     If(self.din_ready,
+            #         w.valid.eq(1),
+            #         NextState("WRITE")
+            #     )
+            # )
+            write_fsm.act("WRITE",
+                w.ready.eq(1),
+                If(w.ready & w.last,
+                    NextState("WRITE_RESP")
+                )
             )
-        )
-        write_fsm.act("WRITE",
-            w.valid.eq(1),
-            If(w.ready & w.last,
-                NextState("IDLE")
+
+            write_fsm.act("WRITE_RESP",
+                port.we.eq(0),
+                b.resp.eq(axi.Response.okay.value),
+                b.valid.eq(1),
+                If(b.ready,
+                    NextState("IDLE")
+                )
             )
-        )
 
-        # refer to port.we instead
-        self.sync += If(w.ready & w.valid, port.we.eq(1))
+            self.sync += If(w.ready & w.valid, port.we.eq(1))
 
-        self.sync += [
-            If(write_fsm.ongoing("IDLE"),
-                self.din_index.eq(0) 
-            ), # but need to synchronise the address too
-            If(w.ready & w.valid, self.din_index.eq(self.din_index+1), port.adr.eq(port.addr+self.din_index))
-        ]
-
-        self.comb += [
-            w.last.eq(0),
-            If(self.din_index==aw.len, w.last.eq(1))
-        ]
+            self.sync += [
+                If(write_fsm.ongoing("IDLE"),
+                    self.din_index.eq(0) 
+                ), # but need to synchronise the address too)
+            ]
 
 
         # # generate write enable signal