Echelon Neuron C - Manual (Page 89)

Neuron C Programmer’s Guide 77
// and allow for its use even if the target device doesn't support
// system extensions. See text for details, and see the Neuron C
// Reference Guide, Compiler Directives, for details about these
// directives.
#pragma system_image_extensions nv_length_override
#pragma unknown_system_image_extension_isa_warning
// see text!
// changeLength() performs or rejects the type change request.
// It is called from the director function in response to a
// device reset because the SCPTnvType has been declared with
// "cp_info(reset_required)." Other CP flags, such as
// object_disabled, require a different invocation. SCPTnvType
// may also be implemented as a configuration network variable,
// allowing for invocation of the changeLength() function from
// a "when(nv_update_occurs(...))" task.
void changeLength(void) {
// First, check to see if there is anything to do at all:
// is there a real type change request pending? The
// changeLength() function could have been invoked as a
// result of a regular device reset (or whichever other
// update notification event is associated with the nvType CP).
if ((nvoVolt::nvType.type_category != NVT_CAT_NUL)
&& (memcmp((void*)&nvTypeLastGood,(void*)&nvoVolt::nvType,
sizeof(SCPTnvType)) != 0)) {
// In case multiple network variables share the same
// SCPTnvType configuration property, make sure all
// affected network variables are unbound. Use is_bound()
// for all these network variables and reject the type change
// if any reports being bound.
// Check if requested type is within acceptable size
// limits. The sizeof(nvoVolt) function always returns the
// initial size of the network variable, which equals
// its maximum size.
if (nvoVolt::nvType.type_length > sizeof(nvoVolt)) {
// Reject: set the nvType CP back to the last known
// good value, log the error, and notify the
// network tool. In addition to the minimum
// requirements, this example implementation
// also automatically disables the fblock
nvoVolt::nvType
= nvTypeLastGood;
error_log(TYPE_ERROR);
getObjStatus(fbSensor::global_index)->invalid_request
= TRUE;
updateNode_Status();
setFblockDisable(fbSensor::global_index,
TRUE);
} else switch (nvoVolt::nvType.type_category) {
case NVT_CAT_SIGNED_LONG:
case NVT_CAT_UNSIGNED_LONG:
case NVT_CAT_FLOAT:
// Accept long and float.
// Store the current type information and, for
// debugging purpose only, also change the length of
// the network variable via its nv_len property. See
// further below for an example implementation of the
// recommended get_nv_length_override technique for
// this network variable.
nvTypeLastGood
= nvoVolt::nvType;
#ifdef _DEBUG // see text!
nvoVolt::nv_len
= nvoVolt::nvType.type_length;