added P4v1.1 sample program with demo

p4v1_1/simple_router/README.md

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+# P4 v1.1 Simple Router
+
+## Description
+
+This program is a version of the now famous simple_router program, written
+according to the P4 v1.1 specification. In addition to the original
+simple_router, this version can keep track of the number of IPv4 packets dropped
+because of an expired TTL. This was added to illustrate some of P4 v1.1 more
+advanced capabilities.
+For more information on P4 v1.1, please refer to [p4.org] (http://p4.org/spec/).
+
+Look at the [P4 program] (p4src/simple_router.p4) and observe some of the P4
+v1.1 additions:
+- strong typing in header type definitions and action declarations
+- assignment with `=` instead of `modify_field` (extension to the v1.1 spec)
+- register indexing
+- support for the ternary operator (extension to the v1.1 spec)
+
+### Running the demo
+
+We provide a small demo to let you test the program. Before trying to run the
+demo, please make sure that your [env.sh] (../env.sh) file is up-to-date.
+
+To run the demo:
+- start the switch in Mininet with `./run_switch.sh`
+- in another terminal, populate the table entries with `./add_entries.sh`
+- you should now be able to ping h2 from h1 by typing `h1 ping h2` in the
+  Mininet CLI
+
+Once you have the basic demo running, you can start sending packets with a TTL
+of 1, activate packet drop tracking in the switch and observe the count go
+up. To do this:
+- activate the tracking with `./register_on_off.sh on`
+- send ICMP packets with a TTL of 1 from the Mininet CLI: `h1 ping h2 -t 1`. The
+  packets are now dropped by the switch, so you should not be able to observe a
+  reply
+
+To get the drop count, simply run `./read_register.sh`.