doc/manual: driver writing tutorial

doc/manual/index.rst

@@ -8,6 +8,7 @@ Contents:
 
     installing
     getting_started
+    writing_a_driver
     core_language_reference
     core_drivers_reference
     management_reference

doc/manual/writing_a_driver.rst

@@ -0,0 +1,97 @@
+Writing a driver
+================
+
+These instructions cover writing a simple driver for a "slow" device, that uses the controller paradigm.
+
+The controller
+--------------
+
+A controller is a piece of software that receives commands from a client over the network (or the ``localhost`` interface), drives a device, and returns information about the device to the client. The mechanism used is remote procedure calls (RPCs) using :class:`artiq.management.pc_rpc`, which makes the network layers transparent for the driver's user.
+
+The controller we will develop is for a "device" that is very easy to work with: the console from which the controller is run. The operation that the driver will implement is writing a message to that console.
+
+For using RPC, the functions that a driver provides must be the methods of a single object. We will thus define a class that provides our message-printing method: ::
+
+    class Hello:
+        def message(self, msg):
+            print("message: " + msg)
+
+To turn it into a server, we use :class:`artiq.management.pc_rpc`. Import the function we will use: ::
+
+    from artiq.management.pc_rpc import simple_server_loop
+
+and add a ``main`` function that is run when the program is executed: ::
+
+    def main():
+        simple_server_loop(Hello(), "::1", 7777)
+
+    if __name__ == "__main__":
+        main()
+
+The parameters ``::1`` and 7777 are respectively the address to bind the server to (IPv6 localhost) and the TCP port to use. Then add a line: ::
+
+    #!/usr/bin/env python3
+
+at the beginning of the file, save it to ``hello-controller`` and set its execution permissions: ::
+
+    $ chmod 755 hello-controller
+
+Run it as: ::
+
+    $ ./hello-controller
+
+and verify that you can connect to the TCP port: ::
+
+    $ telnet ::1 7777
+    Trying ::1...
+    Connected to ::1.
+    Escape character is '^]'.
+
+:tip: Use the key combination Ctrl-AltGr-9 to get the ``telnet>`` prompt, and enter ``close`` to quit Telnet. Quit the controller with Ctrl-C.
+
+The client
+----------
+
+Create a ``hello-client`` file with the following contents: ::
+
+    #!/usr/bin/env python3
+
+    from artiq.management.pc_rpc import Client
+
+
+    def main():
+        remote = Client("::1", 7777)
+        try:
+            remote.message("Hello World!")
+        finally:
+            remote.close_rpc()
+
+    if __name__ == "__main__":
+        main()
+
+Run it as before, while the controller is running. You should see the message appearing on the controller's terminal: ::
+
+    $ ./hello-controller
+    message: Hello World!
+
+
+Command-line arguments
+----------------------
+
+Use the Python ``argparse`` module to make the bind address and port configurable on the controller, and the server address, port and message configurable on the client.
+
+We suggest naming the controller parameters ``--bind`` and ``--port`` so that those parameters stay consistent across controller, and use ``-s/--server`` and ``--port`` on the client.
+
+The controller's code would contain something similar to this: ::
+
+    def _get_args():
+        parser = argparse.ArgumentParser(description="Hello world controller")
+        parser.add_argument("--bind", default="::1",
+                            help="hostname or IP address to bind to")
+        parser.add_argument("--port", default=7777, type=int,
+                            help="TCP port to listen to")
+        return parser.parse_args()
+
+    def main():
+        args = _get_args()
+        simple_server_loop(Hello(), args.bind, args.port)