Revisit waveform initialisation

Ensure that the waveform type and length are specified during record
creation to avoid problems with .set() later on.

Author: Araneidae

softioc/builder.py

@@ -7,7 +7,8 @@
 InitialiseDbd()
 LoadDbdFile(os.path.join(os.path.dirname(__file__), 'device.dbd'))
 
-from . import pythonSoftIoc  # noqa
+from . import device, pythonSoftIoc  # noqa
+
 PythonDevice = pythonSoftIoc.PythonDevice()
 
 
@@ -120,7 +121,7 @@ def Action(name, **fields):
     'l':    'LONG',         # int_
     'f':    'FLOAT',        # single
     'd':    'DOUBLE',       # float_
-    'S':    'STRING',       # str_
+#     'S':    'STRING',       # str_
 
     # The following type codes are weakly supported by pretending that
     # they're related types.
@@ -135,6 +136,19 @@ def Action(name, **fields):
     #   O   object_         U   unicode_        V   void
 }
 
+# Coverts FTVL string to numpy type
+DbfStringToNumpy = {
+#     'STRING':   numpy.dtype('S40'),       # Don't think we want this!
+    'CHAR':     numpy.dtype('int8'),
+    'UCHAR':    numpy.dtype('uint8'),
+    'SHORT':    numpy.dtype('int16'),
+    'USHORT':   numpy.dtype('uint16'),
+    'LONG':     numpy.dtype('int32'),
+    'ULONG':    numpy.dtype('uint32'),
+    'FLOAT':    numpy.dtype('float32'),
+    'DOUBLE':   numpy.dtype('float64'),
+}
+
 
 def _waveform(value, fields):
     '''Helper routine for waveform construction.  If a value is given it is
@@ -146,29 +160,34 @@ def _waveform(value, fields):
         assert not value, 'Can\'t specify initial value twice!'
         value = (fields.pop('initial_value'),)
 
+    # Datatype can be specified as keyword argument, taken from FTVL, or derived
+    # from the initial value
+    if 'datatype' in fields:
+        assert 'FTVL' not in fields, \
+            'Can\'t specify FTVL and datatype together'
+        datatype = numpy.dtype(fields.pop('datatype'))
+    elif 'FTVL' in fields:
+        datatype = DbfStringToNumpy[fields['FTVL']]
+    else:
+        # No datatype specified, will have to infer from initial value
+        datatype = None
+
     if value:
-        # If a value is specified it should be the *only* non keyword
-        # argument.
+        # If a value is specified it should be the *only* non keyword argument.
         value, = value
-        value = numpy.array(value)
-        fields['initial_value'] = value
-
-        # Pick up default length and datatype from initial value
-        length = len(value)
-        FTVL = NumpyCharCodeToFtvl[value.dtype.char]
+        initial_value = device._require_waveform(value, datatype)
+        length = fields.pop('length', len(initial_value))
     else:
-        # No value specified, so require length and datatype to be specified.
+        initial_value = numpy.array([], dtype = datatype)
         length = fields.pop('length')
-        FTVL = 'FLOAT'
+    datatype = initial_value.dtype
 
-    datatype = fields.pop('datatype', None)
-    if datatype is not None:
-        assert 'FTVL' not in fields, \
-            'Can\'t specify FTVL and datatype together'
-        FTVL = NumpyCharCodeToFtvl[numpy.dtype(datatype).char]
+    fields['initial_value'] = initial_value
+    fields['_wf_nelm'] = length
+    fields['_wf_dtype'] = datatype
 
     fields['NELM'] = length
-    fields.setdefault('FTVL', FTVL)
+    fields['FTVL'] = NumpyCharCodeToFtvl[datatype.char]
 
 
 def Waveform(name, *value, **fields):
@@ -191,6 +210,10 @@ def _long_string(fields):
         # Default length of 256
         length = 256
 
+    fields.setdefault('initial_value', '')
+    fields['_wf_nelm'] = length
+    fields['_wf_dtype'] = numpy.dtype('uint8')
+
     fields['NELM'] = length
     fields['FTVL'] = 'UCHAR'
 

softioc/device.py

@@ -314,6 +314,14 @@ class ao(ProcessDeviceSupportOut):
     _dbf_type_ = fields.DBF_DOUBLE
 
 
+def _require_waveform(value, dtype):
+    value = numpy.require(value, dtype = dtype)
+    if value.shape == ():
+        value.shape = (1,)
+    assert value.ndim == 1, 'Can\'t write multidimensional arrays'
+    return value
+
+
 class WaveformBase(ProcessDeviceSupportCore):
     _link_ = 'INP'
     # In the waveform record class, the following four fields are key:
@@ -322,16 +330,15 @@ class WaveformBase(ProcessDeviceSupportCore):
     #   NELM    Length of allocated array in number of elements
     #   NORD    Currently reported length of array (0 <= NORD <= NELM)
     _fields_ = ['UDF', 'FTVL', 'BPTR', 'NELM', 'NORD']
-    # Allow set() to be called before init_record:
-    _dtype = None
 
-    def _default_value(self):
-        return numpy.array([])
+
+    def __init__(self, name, _wf_nelm, _wf_dtype, **kargs):
+        self._dtype = _wf_dtype
+        self._nelm = _wf_nelm
+        self.__super.__init__(name, **kargs)
 
     def init_record(self, record):
-        self._nelm = record.NELM
         self._dbf_type_ = record.FTVL
-        self._dtype = fields.DbfCodeToNumpy[record.FTVL]
         return self.__super.init_record(record)
 
     def _read_value(self, record):
@@ -343,12 +350,7 @@ def _read_value(self, record):
         return result
 
     def _write_value(self, record, value):
-        value = numpy.require(value, dtype = self._dtype)
-
-        nelm = record.NELM
         nord = len(value)
-        if nord > nelm:
-            nord = nelm
         memmove(
             record.BPTR, value.ctypes.data_as(c_void_p),
             self._dtype.itemsize * nord)
@@ -360,26 +362,17 @@ def _compare_values(self, value, other):
     def _value_to_epics(self, value):
         # Ensure we always convert incoming value into numpy array, regardless
         # of whether the record has been initialised or not
-        value = numpy.require(value, dtype = self._dtype)
-        if value.shape == ():
-            value.shape = (1,)
-        assert value.ndim == 1, 'Can\'t write multidimensional arrays'
-
-        # Truncate value to fit
-        if hasattr(self, '_nelm'):
-            value = value[:self._nelm]
-
+        value = _require_waveform(value, self._dtype)
         # Because arrays are mutable values it's ever so easy to accidentially
         # call set() with a value which subsequently changes.  To avoid this
         # common class of bug, at the cost of duplicated code and data, here we
-        # ensure a copy is taken of the value.
-        return +value
+        # ensure a copy is taken of the value, after pruning to length.
+        return +value[:self._nelm]
 
     def _epics_to_value(self, value):
         return value
 
     def _value_to_dbr(self, value):
-        value = numpy.require(value, dtype = self._dtype)
         return self._dbf_type_, len(value), value.ctypes.data, value
 
 

softioc/fields.py

@@ -42,19 +42,6 @@
     DBF_NOACCESS: c_void_p,
 }
 
-# Mapping for record field type to numpy type.
-DbfCodeToNumpy = {
-    DBF_STRING: numpy.dtype('S40'),
-    DBF_CHAR: numpy.dtype('int8'),
-    DBF_UCHAR: numpy.dtype('uint8'),
-    DBF_SHORT: numpy.dtype('int16'),
-    DBF_USHORT: numpy.dtype('uint16'),
-    DBF_LONG: numpy.dtype('int32'),
-    DBF_ULONG: numpy.dtype('uint32'),
-    DBF_FLOAT: numpy.dtype('float32'),
-    DBF_DOUBLE: numpy.dtype('float64'),
-}
-
 # Mapping from basic DBR_ codes to DBF_ values
 DbrToDbfCode = {
     DBR_STRING: DBF_STRING,

softioc/pythonSoftIoc.py

@@ -23,8 +23,8 @@ def __init__(self, builder, device, name, **fields):
         # remaining arguments are passed to the builder.  It's a shame we
         # have to maintain this separately from the corresponding device list.
         DeviceKeywords = [
-            'on_update', 'on_update_name', 'validate',
-            'initial_value', 'always_update']
+            'on_update', 'on_update_name', 'validate', 'always_update',
+            'initial_value', '_wf_nelm', '_wf_dtype']
         device_kargs = {}
         for keyword in DeviceKeywords:
             if keyword in fields: