auart_hd.py added. Tutorial amended to suit.

Author: peterhinch

README.md

@@ -2,8 +2,7 @@
 
 This GitHub repository consists of the following parts:
  * [A tutorial](./TUTORIAL.md) An introductory tutorial on asynchronous
- programming and the use of the uasyncio library is offered. This is a work in
- progress, not least because uasyncio is not yet complete.
+ programming and the use of the uasyncio library is offered.
  * [Asynchronous device drivers](./DRIVERS.md). A module providing drivers for
  devices such as switches and pushbuttons.
  * [Synchronisation primitives](./PRIMITIVES.md). Provides commonly used

TUTORIAL.md

@@ -123,6 +123,8 @@ and rebuilding.
 
   5.1 [The IORead mechnaism](./TUTORIAL.md#51-the-ioread-mechanism)
 
+   5.1.1 [A UART driver example](./TUTORIAL.md#511-a-uart-driver-example)
+
   5.2 [Using a coro to poll hardware](./TUTORIAL.md#52-using-a-coro-to-poll-hardware)
 
   5.3 [Using IORead to poll hardware](./TUTORIAL.md#53-using-ioread-to-poll-hardware)
@@ -211,6 +213,9 @@ results by accessing Pyboard hardware.
  8. `aqtest.py` Demo of uasyncio `Queue` class.
  9. `aremote.py` Example device driver for NEC protocol IR remote control.
  10. `auart.py` Demo of streaming I/O via a Pyboard UART.
+ 11. `auart_hd.py` Use of the Pyboard UART to communicate with a device using a
+ half-duplex protocol. Suits devices such as those using the 'AT' modem command
+ set.
 
 **Test Programs**
 
@@ -1033,6 +1038,28 @@ The mechanism works because the device driver (written in C) implements the
 following methods: `ioctl`, `read`, `write`, `readline` and `close`. See
 section 5.3 for further discussion.
 
+### 5.1.1 A UART driver example
+
+The program `auart_hd.py` illustrates a method of communicating with a half
+duplex device such as one responding to the modem 'AT' command set. Half duplex
+means that the device never sends unsolicited data: its transmissions are
+always in response to a command from the master.
+
+The device is emulated, enabling the test to be run on a Pyboard with two wire
+links.
+
+The (highly simplified) emulated device responds to any command by sending four
+lines of data with a pause between each, to simulate slow processing.
+
+The master sends a command, but does not know in advance how many lines of data
+will be returned. It starts a retriggerable timer, which is retriggered each
+time a line is received. When the timer times out it is assumed that the device
+has completed transmission, and a list of received lines is returned.
+
+The case of device failure is also demonstrated. This is done by omitting the
+transmission before awaiting a response. After the timeout an empty list is
+returned. See the code comments for more details.
+
 ###### [Contents](./TUTORIAL.md#contents)
 
 ## 5.2 Using a coro to poll hardware

auart_hd.py

@@ -0,0 +1,106 @@
+# auart_hd.py
+# Author: Peter Hinch
+# Copyright Peter Hinch 2018 Released under the MIT license
+
+# Demo of running a half-duplex protocol to a device. The device never sends
+# unsolicited messages. An example is a communications device which responds
+# to AT commands.
+# The master sends a message to the device, which may respond with one or more
+# lines of data. The master assumes that the device has sent all its data when
+# a timeout has elapsed.
+
+# In this test a physical device is emulated by the DEVICE class
+# To test link X1-X4 and X2-X3
+
+from pyb import UART
+import uasyncio as asyncio
+import aswitch
+
+# Dummy device waits for any incoming line and responds with 4 lines at 1 second
+# intervals.
+class DEVICE():
+    def __init__(self, uart_no = 4):
+        self.uart = UART(uart_no, 9600)
+        self.loop = asyncio.get_event_loop()
+        self.swriter = asyncio.StreamWriter(self.uart, {})
+        self.sreader = asyncio.StreamReader(self.uart)
+        loop = asyncio.get_event_loop()
+        loop.create_task(self._run())
+
+    async def _run(self):
+        responses = ['Line 1', 'Line 2', 'Line 3', 'Goodbye']
+        while True:
+            res = await self.sreader.readline()
+            for response in responses:
+                await self.swriter.awrite("{}\r\n".format(response))
+                # Demo the fact that the master tolerates slow response.
+                await asyncio.sleep_ms(300)
+
+# The master's send_command() method sends a command and waits for a number of
+# lines from the device. The end of the process is signified by a timeout, when
+# a list of lines is returned. This allows line-by-line processing.
+# A special test mode demonstrates the behaviour with a non-responding device. If
+# None is passed, no commend is sent. The master waits for a response which never
+# arrives and returns an empty list.
+class MASTER():
+    def __init__(self, uart_no = 2, timeout=4000):
+        self.uart = UART(uart_no, 9600)
+        self.timeout = timeout
+        self.loop = asyncio.get_event_loop()
+        self.swriter = asyncio.StreamWriter(self.uart, {})
+        self.sreader = asyncio.StreamReader(self.uart)
+        self.delay = aswitch.Delay_ms()
+        self.response = []
+        loop = asyncio.get_event_loop()
+        loop.create_task(self._recv())
+
+    async def _recv(self):
+        while True:
+            res = await self.sreader.readline()
+            self.response.append(res)  # Append to list of lines
+            self.delay.trigger(self.timeout)  # Got something, retrigger timer
+
+    async def send_command(self, command):
+        self.response = []  # Discard any pending messages
+        if command is None:
+            print('Timeout test.')
+        else:
+            await self.swriter.awrite("{}\r\n".format(command))
+            print('Command sent:', command)
+        self.delay.trigger(self.timeout)  # Re-initialise timer
+        while self.delay.running():
+            await asyncio.sleep(1)  # Wait for 4s after last msg received
+        return self.response
+
+async def test():
+    print('This test takes 10s to complete.')
+    for cmd in ['Run', None]:
+        print()
+        res = await master.send_command(cmd)
+        # can use b''.join(res) if a single string is required.
+        if res:
+            print('Result is:')
+            for line in res:
+                print(line.decode('UTF8'), end='')
+        else:
+            print('Timed out waiting for result.')
+
+loop = asyncio.get_event_loop()
+master = MASTER()
+device = DEVICE()
+loop.run_until_complete(test())
+
+# Expected output
+# >>> import auart_hd
+# This test takes 10s to complete.
+#
+# Command sent: Run
+# Result is:
+# Line 1
+# Line 2
+# Line 3
+# Goodbye
+#
+# Timeout test.
+# Timed out waiting for result.
+# >>>