freq counter: refactor

use CSR instead of CSRStatus
add FSM to support CSR

src/gateware/wrpll.py

@@ -8,47 +8,56 @@ from si549 import Si549
 
 class FrequencyCounter(Module, AutoCSR):
     def __init__(self, domains, counter_width=24):
-        for domain in domains:
-            name = "counter_" + domain
-            counter = CSRStatus(counter_width, name=name)
-            setattr(self, name, counter)
-        self.update_en = CSRStorage()
+        self.update = CSR()
+
+        counter_reset = Signal()
+        counter_stb = Signal()
+        timer = Signal(max=2**counter_width)
 
         # # #
 
-        timer = Signal(counter_width)
-        timer_tick = Signal()
-        self.sync +=[
-            If(self.update_en.storage, 
-                Cat(timer, timer_tick).eq(timer + 1)
-            ).Else(
-                Cat(timer, timer_tick).eq(0)
+        fsm = FSM()
+        self.submodules += fsm
+
+        fsm.act("IDLE",
+            If(self.update.re,
+                counter_reset.eq(1),
+                NextValue(timer, 2**counter_width - 1),
+                NextState("COUNTING")
             )
-        ]
+        )
+        fsm.act("COUNTING",
+            If(timer != 0,
+                NextValue(timer, timer - 1)
+            ).Else( 
+                counter_stb.eq(1),
+                NextState("IDLE")
+            )
+        )
 
         for domain in domains:
-            sync_domain = getattr(self.sync, domain)
             divider = Signal(2)
-            sync_domain += divider.eq(divider + 1)
-
-            divided = Signal()
-            sync_domain += divided.eq(divider[-1])
             divided_sys = Signal()
-            self.specials += MultiReg(divided, divided_sys)
-
             divided_sys_r = Signal()
-            divided_tick = Signal()
+            rising = Signal()
+
+            name = "counter_" + domain
+            counter_csr = CSRStatus(counter_width, name=name)
+            setattr(self, name, counter_csr)
+            counter = Signal(counter_width)
+
+            sync_domain = getattr(self.sync, domain)
+            sync_domain += divider.eq(divider + 1)
+            self.specials += MultiReg(divider[-1], divided_sys)
             self.sync += [
                 divided_sys_r.eq(divided_sys),
-                divided_tick.eq(divided_sys & ~divided_sys_r)
+                rising.eq(divided_sys & ~divided_sys_r)
             ]
 
-            counter = Signal(counter_width)
-            counter_csr = getattr(self, "counter_" + domain)
             self.sync += [
-                If(timer_tick, counter_csr.status.eq(counter)),
-                If(divided_tick, counter.eq(counter + 1)),
-                If(~self.update_en.storage, counter.eq(0)),
+                If(counter_reset, counter.eq(0)),
+                If(rising, counter.eq(counter + 1)),
+                If(counter_stb, counter_csr.status.eq(counter))
             ]
 
 class SkewTester(Module, AutoCSR):