init commit for ATE levels generator

text/0004-ate-levels-generator.md

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+- Nov, 6th 2017
+- RFC PR: (leave this empty)
+- Implementation PR: (leave this empty)
+
+# Summary
+
+Create an ATE levels generator framework that will work across tester platforms, using the V93K as a POC
+
+# Motivation
+
+Directly supports getting Origen to v1.0 and checks off another test program collateral
+
+# Detailed design
+
+The first issue is to define what the source of truth is when making ATE levels.  ATE levels are determined by
+the following components:
+
+1. Device power domain specifications
+2. ATE guardband based on ATE specific power supply and PEC accuracies
+3. Test operation guardbands based on company/product specific business logic (i.e. relaxing at wafer sort due to contact resistance)
+
+How can we store this information currently in Origen?
+
+1. Origen::Specs can be applied to the DUT, sub_blocks, and power domains
+2. Origen::PowerDomains can store nominal voltage and maximum voltage rating but currently does not include min, max specs
+3. Origen::Parameters has a very flexible API for storing all sorts of data but it has no domain specific logic regarding ATE levels
+
+The question we need to answer is where does the ATE levels generator go for these bits of information?  Let's examine each of the types of information
+and sketch out a possible API.
+
+1. Power domian specs: The first need is to add min and max spec limits to the model.
+
+~~~ruby
+$dut.power_domain :vdd do |d|
+  d.description = 'Core power domain'
+  d.nominal_voltage = 1.0.V
+  d.mvr = 1.35.V
+end
+$dut.power_domains(:vdd).spec :vdd, :dc do |s|
+  s.description = 'Core power domain voltage'
+  s.min = 0.8.V
+  s.max = 1.2.V
+end
+~~~
+
+I showed this to my team and they were not fans, as it seems like duplication and a chance for error.  Using the API is also cumbersome:
+
+~~~shell
+peologin01 $ $dut.power_domains(:vdd).nominal_voltage # => 1.0
+peologin01 $ $dut.power_domains(:vdd).specs(:vdd).min # => 0.8
+peologin01 $ $dut.power_domains(:vdd).specs(:vdd).min # => 1.2
+~~~
+
+But I think some simple min, max methods could allow users to still use Origen::Specs and define power domains like this:
+
+~~~ruby
+$dut.power_domain :vdd do |d|
+  d.description = 'Core power domain'
+  d.nominal_voltage = 1.0.V
+  d.mvr = 1.35.V
+  d.min = 0.8.V
+  d.max = 1.2.V
+end
+~~~
+
+OK, so the next part to handle is how and where to store the power domain settings for each test operation.  We have an OrigenSourceFileCreator
+module that interrogates dut.power_domains and dut.test_flow to create a bunch of test condition inspried parameter sets.
+
+~~~ruby
+module PPEKit
+  class Product
+    def define_levels_params
+      define_params :pnom do |p|
+        p.vddno1.oper1 = 0.9
+        p.vddno1.oper2 = 0.9
+        p.vddno1.oper3 = 0.9
+        p.vddno2.oper1 = 0.9
+        p.vddno2.oper2 = 0.9
+        p.vddno2.oper3 = 0.9
+        p.vddno3.oper1 = 0.9
+        p.vddno3.oper2 = 0.9
+        p.vddno3.oper3 = 0.9
+~~~
+
+Now this is where it starts to get sticky. Where do we expect folks to keep this data?  Origen::Parameters is very flexible but has no domain knowledge.
+Before I continue on with the RFC I think everyone invoved needs to provide feedback on what I have so far.
+
+# Drawbacks
+
+TBD
+
+# Unresolved questions
+
+- where to store level sets info
+- where to store level eqn info (API similar to Origen timings?)
+- how to implement ATE platform specific guardbands.  I believe we should start modeling the actual supplies and PECs and allow users
+  to model their tester config to whatever detail is necessary to implement guardbands.