soc/cores/timer/doc: rewrite a little bit, avoid some redundancy, change ident.

litex/soc/cores/timer.py

@@ -1,4 +1,6 @@
 # This file is Copyright (c) 2013-2015 Sebastien Bourdeauducq <sb@m-labs.hk>
+# This file is Copyright (c) 2019 Sean Cross <sean@xobs.io>
+# This file is Copyright (c) 2019 Florent Kermarrec <florent@enjoy-digital.fr>
 # License: BSD
 
 
@@ -10,22 +12,19 @@ from litex.soc.interconnect.csr_eventmanager import *
 
 class Timer(Module, AutoCSR):
     def __init__(self, width=32):
-        self._load = CSRStorage(width, description="""This is the initial value loaded into the
+        self._load = CSRStorage(width, description=
-                                        timer.  You can make a one-shot timer by disabling the
+            """Load value when timer is (re-)enabled.
-                                        timer, writing to this register, and then re-enabling
+            This register is only used to create a One-Shot timer and specify the timer's duration
-                                        the timer.  For a recurring timer, set this to the same
+            in clock cycles: Disable the timer, write load value and re-enable the timer""")
-                                        value as `reload`, or to 0.""")
+        self._reload = CSRStorage(width, description=
-        self._reload = CSRStorage(width, description="""The internal timer value will be updated
+            """Reload value when timer reaches 0.
-                                        with this value whenever it reaches 0.  Use this to create
+            This register is used to create a Periodic timer and specify the timer's period in clock
-                                        a periodic timer that fires whenever this transitions from
+            cycles. For a One-Shot timer, this register need to be set to 0.""")
-                                        0 to >0.  To create a one-shot timer, leave this value as 0.""")
+        self._en = CSRStorage(1, description=
-        self._en = CSRStorage(fields=[CSRField("en", description="Write a `1` here to start the timer running")])
+            """Enable. Write 1 to enable/start the timer, 0 to disable the timer""")
-        self._update_value = CSRStorage(fields=[CSRField("update", description="""Writing to this register causes
+        self._update_value = CSRStorage(1, description=
-                                        the `value` register to be updated with with the current countdown
+            """Update. Write 1 to latch current countdown to value register.""")
-                                        value.""")])
+        self._value = CSRStatus(width, description="""Latched countdown value""")
-        self._value = CSRStatus(width, description="""Last snapshotted value of the countdown
-                                        timer.  This value is only updated when a `1` is written
-                                        to `update_value`.""")
 
         self.submodules.ev = EventManager()
         self.ev.zero = EventSourceProcess()