Moved the simple_por ngspice simulations into directory ngspice/simple_por/.
Added new directory ngspice/digital_pll/ containing simulation testbenches for
the digital PLL and trimmable ring oscillator.  Added qflow directories for
both;  this was done only to get a valid xspice file for the controller and
a valid SPICE netlist for the ring oscillator.

qflow/ring_osc2x13/qflow_vars.sh

diff --git a/qflow/ring_osc2x13/qflow_vars.sh b/qflow/ring_osc2x13/qflow_vars.sh
new file mode 100644
index 0000000..cb887d8
--- /dev/null
+++ b/qflow/ring_osc2x13/qflow_vars.sh
@@ -0,0 +1,17 @@
+#!/bin/tcsh -f
+#-------------------------------------------
+# qflow variables for project ~/gits/caravel/qflow/ring_osc2x13
+#-------------------------------------------
+
+set qflowversion=1.4.80
+set projectpath=~/gits/caravel/qflow/ring_osc2x13
+set techdir=~/gits/caravel/qflow/ring_osc2x13/tech
+set sourcedir=~/gits/caravel/qflow/ring_osc2x13/source
+set synthdir=~/gits/caravel/qflow/ring_osc2x13/synthesis
+set layoutdir=~/gits/caravel/qflow/ring_osc2x13/layout
+set techname=sky130Ahd
+set scriptdir=/usr/local/share/qflow/scripts
+set bindir=/usr/local/share/qflow/bin
+set logdir=~/gits/caravel/qflow/ring_osc2x13/log
+#-------------------------------------------
+