timer: add prescaler

diff --git a/misoclib/cpu/peripherals/timer/__init__.py b/misoclib/cpu/peripherals/timer/__init__.py
index 2ab77eadccc23dd2c1eb3ffa7c0259a7074f0c30..22e4d75c638b84ca36c6f6d4b8bde1075099b995 100644 (file)
--- a/misoclib/cpu/peripherals/timer/__init__.py
+++ b/misoclib/cpu/peripherals/timer/__init__.py
@@ -1,12 +1,14 @@
 from migen.fhdl.std import *
 from migen.bank.description import *
 from migen.bank.eventmanager import *
+from migen.genlib.misc import Counter
 
 class Timer(Module, AutoCSR):
-       def __init__(self, width=32):
+       def __init__(self, width=32, prescaler_width=32):
                self._load = CSRStorage(width)
                self._reload = CSRStorage(width)
                self._en = CSRStorage()
+               self._prescaler = CSRStorage(prescaler_width, reset=1)
                self._update_value = CSR()
                self._value = CSRStatus(width)
 
@@ -15,14 +17,28 @@ class Timer(Module, AutoCSR):
                self.ev.finalize()
 
                ###
+               enable = self._en.storage
+               tick = Signal()
+
+               counter = Counter(prescaler_width)
+               self.submodules += counter
+               self.comb += [
+                       If(enable,
+                               tick.eq(counter.value >= (self._prescaler.storage-1)),
+                               counter.ce.eq(1),
+                               counter.reset.eq(tick),
+                       ).Else(
+                               counter.reset.eq(1)
+                       )
+               ]
 
                value = Signal(width)
                self.sync += [
-                       If(self._en.storage,
+                       If(enable,
                                If(value == 0,
                                        # set reload to 0 to disable reloading
                                        value.eq(self._reload.storage)
-                               ).Else(
+                               ).Elif(tick,
                                        value.eq(value - 1)
                                )
                        ).Else(