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80 lines
3.3 KiB
Python
80 lines
3.3 KiB
Python
# This file is Copyright (c) 2013-2015 Sebastien Bourdeauducq <sb@m-labs.hk>
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# This file is Copyright (c) 2019 Sean Cross <sean@xobs.io>
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# This file is Copyright (c) 2019 Florent Kermarrec <florent@enjoy-digital.fr>
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# License: BSD
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from migen import *
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from litex.soc.interconnect.csr import *
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from litex.soc.interconnect.csr_eventmanager import *
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from litex.soc.integration.doc import ModuleDoc
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# Timer --------------------------------------------------------------------------------------------
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class Timer(Module, AutoCSR, ModuleDoc):
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"""Timer
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Provides a generic Timer core.
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The Timer is implemented as a countdown timer that can be used in various modes:
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- Polling : Returns current countdown value to software.
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- One-Shot: Loads itself and stops when value reaches 0.
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- Periodic: (Re-)Loads itself when value reaches 0.
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`en` register allows the user to enable/disable the Timer. When the Timer is enabled, it is
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automatically loaded with the value of `load` register.
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When the Timer reaches 0, it is automatically reloaded with value of `reload` register.
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The user can latch the current countdown value by writing to `update_value` register, it will
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update `value` register with current countdown value.
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To use the Timer in One-Shot mode, the user needs to:
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- Disable the timer.
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- Set the `load` register to the expected duration.
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- (Re-)Enable the Timer.
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To use the Timer in Periodic mode, the user needs to:
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- Disable the Timer.
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- Set the `load` register to 0.
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- Set the `reload` register to the expected period.
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- Enable the Timer.
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For both modes, the CPU can be advertised by an IRQ that the duration/period has elapsed. (The
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CPU can also do software polling with `update_value` and `value` to know the elapsed duration)
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"""
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def __init__(self, width=32):
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self._load = CSRStorage(width, description="""Load value when Timer is (re-)enabled.""" +
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"""In One-Shot mode, the value written to this register specify the Timer's duration in
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clock cycles.""")
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self._reload = CSRStorage(width, description="""Reload value when Timer reaches 0.""" +
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"""In Periodic mode, the value written to this register specify the Timer's period in
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clock cycles.""")
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self._en = CSRStorage(1, description="""Enable of the Timer.""" +
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"""Set if to 1 to enable/start the Timer and 0 to disable the Timer""")
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self._update_value = CSRStorage(1, description="""Update of the current countdown value."""+
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"""A write to this register latches the current countdown value to `value` register.""")
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self._value = CSRStatus(width, description="""Latched countdown value""")
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self.submodules.ev = EventManager()
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self.ev.zero = EventSourceProcess()
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self.ev.finalize()
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# # #
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value = Signal(width)
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self.sync += [
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If(self._en.storage,
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If(value == 0,
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# set reload to 0 to disable reloading
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value.eq(self._reload.storage)
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).Else(
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value.eq(value - 1)
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)
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).Else(
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value.eq(self._load.storage)
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),
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If(self._update_value.re, self._value.status.eq(value))
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]
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self.comb += self.ev.zero.trigger.eq(value != 0)
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