Subcircuit instance model name are unresolved in CDL netlisting.

[ThomasZecha]

This is a follow-up of the discussion from IHP-GmbH/IHP-Open-PDK#336.

Summary:
In a CDL netlist device hierarchy all nodes must be subcircuits, all leafs must be primitive devices.
This rule is violated in the present case.

One possible solution would be (from original):

Introduce the following per global settings on/off switchable special treatment of subcircuit instances during CDL netlisting:

As a preparation step during CDL netlist export:

1. Found all subcircuit instances in the current schematic.
2. For every instance from 1. check whether the referenced subcircuit exists in the current schematic.
3. For every instance from 2. where the subcircuit don’t exist do:
   a. Check whether the second letter of the instance name refer a CDL primitive device (R, C, L , M, Q, ...)
   b. If a. holds check whether the number of pins match the allowed pin-numbers of the primitive device from a.
   c. If b. holds remove the first letter from the instance name for the CDL-netlisted instance name.

[ra3xdh]

The solution may be to introduce a property named CDL_letter for all devices in Microelectonics group. The default is the same as SPICE letter. Current inplementation of cdl_netlist() method returns the spice_netlist. A separate handling may be required.