introduce FrozenParam
For the case when the readback of a parameter does not reflect the change immediately. May also be used on Writable.target or Drivable.target with a short BUSY period. + bug fix in an error message in frappy.datatypes.IntRange Change-Id: I5e1c871629f9e3940ae80f35cb6307f404202b4a Reviewed-on: https://forge.frm2.tum.de/review/c/secop/frappy/+/31981 Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de> Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>
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123
frappy_psi/frozenparam.py
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123
frappy_psi/frozenparam.py
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# *****************************************************************************
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# This program is free software; you can redistribute it and/or modify it under
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# the terms of the GNU General Public License as published by the Free Software
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# Foundation; either version 2 of the License, or (at your option) any later
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# version.
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#
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# This program is distributed in the hope that it will be useful, but WITHOUT
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# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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# FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
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# details.
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#
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# You should have received a copy of the GNU General Public License along with
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# this program; if not, write to the Free Software Foundation, Inc.,
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# 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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#
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# Module authors:
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# Markus Zolliker <markus.zolliker@psi.ch>
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# *****************************************************************************
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import time
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import math
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from frappy.core import Parameter, FloatRange, IntRange, Property
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from frappy.errors import ProgrammingError
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class FrozenParam(Parameter):
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"""workaround for lazy hardware
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Some hardware does not react nicely: when a parameter is changed,
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and read back immediately, still the old value is returned.
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This special parameter helps fixing this problem.
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Mechanism:
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- after a call to write_<param> for a short time (<n_polls> * <interval>)
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the hardware is polled until the readback changes before the 'changed'
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message is replied to the client
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- if there is no change yet within short time, the 'changed' message is
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set with the given value and further calls to read_<param> return also
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this given value until the readback value has changed or until
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<timeout> sec have passed.
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For float parameters, the behaviour for small changes is improved
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when the write_<param> method tries to return the (may be rounded) value,
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as if it would be returned by the hardware. If this behaviour is not
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known, or the programmer is too lazy to implement it, write_<param>
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should return None or the given value.
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Also it will help to adjust the datatype properties
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'absolute_resolution' and 'relative_resolution' to reasonable values.
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"""
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timeout = Property('timeout for freezing readback value',
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FloatRange(0, unit='s'), default=30)
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n_polls = Property("""number polls within write method""",
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IntRange(0), default=1)
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interval = Property("""interval for polls within write method
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the product n_polls * interval should not be more than a fraction of a second
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in order not to block the connection for too long
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""",
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FloatRange(0, unit='s'), default=0.05)
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new_value = None
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previous_value = None
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expire = 0
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is_float = True # assume float. will be fixed later
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def isclose(self, v1, v2):
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if v1 == v2:
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return True
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if self.is_float:
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dt = self.datatype
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try:
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return math.isclose(v1, v2, abs_tol=dt.absolute_tolerance,
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rel_tol=dt.relative_tolerance)
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except AttributeError:
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# fix once for ever when datatype is not a float
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self.is_float = False
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return False
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def __set_name__(self, owner, name):
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try:
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rfunc = getattr(owner, f'read_{name}')
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wfunc = getattr(owner, f'write_{name}')
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except AttributeError:
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raise ProgrammingError(f'FrozenParam: methods read_{name} and write_{name} must exist') from None
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super().__set_name__(owner, name)
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def read_wrapper(self, pname=name, rfunc=rfunc):
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pobj = self.parameters[pname]
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value = rfunc(self)
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if pobj.new_value is None:
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return value
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if not pobj.isclose(value, pobj.new_value):
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if value == pobj.previous_value:
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if time.time() < pobj.expire:
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return pobj.new_value
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self.log.warning('%s readback did not change within %g sec',
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pname, pobj.timeout)
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else:
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# value has changed, but is not matching new value
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self.log.warning('%s readback changed from %r to %r but %r was given',
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pname, pobj.previous_value, value, pobj.new_value)
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# readback value has changed or returned value is roughly equal to the new value
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pobj.new_value = None
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return value
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def write_wrapper(self, value, wfunc=wfunc, rfunc=rfunc, read_wrapper=read_wrapper, pname=name):
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pobj = self.parameters[pname]
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pobj.previous_value = rfunc(self)
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pobj.new_value = wfunc(self, value)
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if pobj.new_value is None: # as wfunc is the unwrapped write_* method, the return value may be None
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pobj.new_value = value
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pobj.expire = time.time() + pobj.timeout
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for cnt in range(pobj.n_polls):
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if cnt: # we may be lucky, and the readback value has already changed
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time.sleep(pobj.interval)
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value = read_wrapper(self)
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if pobj.new_value is None:
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return value
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return pobj.new_value
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setattr(owner, f'read_{name}', read_wrapper)
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setattr(owner, f'write_{name}', write_wrapper)
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