Add ntptime.py.

README.md

@@ -38,6 +38,7 @@ and modules which are documented and supported.
   4.11 [Functors and singletons](./README.md#411-functors-and-singletons) Useful decorators.  
   4.12 [Quaternions](./README.md#412-quaternions) Scale, move and rotate 3D objects with minimal mathematics.  
   4.13 [A Pyboard power meter](./README.md#413-a-pyboard-power-meter) One of my own projects.  
+  4.14 [NTP time](./README.md#414-ntp-time) More portable than official driver with other benefits.  
  5. [Module Index](./README.md#5-module-index) Supported code. Device drivers, GUI's, utilities.  
   5.1 [uasyncio](./README.md#51-uasyncio) Tutorial and drivers for asynchronous coding.  
   5.2 [Memory Device Drivers](./README.md#52-memory-device-drivers) Drivers for nonvolatile memory devices.  
@@ -297,6 +298,20 @@ enabling it to provide information on power factor and to work with devices
 which generate as well as consume power. It uses the official LCD160CR display
 as a touch GUI interface. It is documented [here](./power/README.md).
 
+## 4.14 NTP Time
+
+The official code has a number of drawbacks, mainly a lack of portability.
+ 1. It does not check the host device's epoch. This version returns the number
+ of seconds since the host device's epoch.
+ 2. It uses socket timeouts while the docs recommend select.poll as being more
+ portable. This version remedies that.
+ 3. This version has very basic support for local time in the form of an offset
+ in hours relative to UTC.
+ 4. In the event of a timeout this version returns 0: the caller should check
+ for this and re-try after a period.
+
+Code is [here](./ntptime/ntptime.py).
+
 ##### [Index](./README.md#0-index)
 
 # 5. Module index

ntptime/ntptime.py

@@ -0,0 +1,35 @@
+# Adapted from official ntptime by Peter Hinch July 2022
+# The main aim is portability:
+# Detects host device's epoch and returns time relative to that.
+# Basic approach to local time: add offset in hours relative to UTC.
+# Timeouts return a time of 0. These happen: caller should check for this.
+# Replace socket timeout with select.poll as per docs:
+# http://docs.micropython.org/en/latest/library/socket.html#socket.socket.settimeout
+
+import socket
+import struct
+import select
+from time import gmtime
+
+# (date(2000, 1, 1) - date(1900, 1, 1)).days * 24*60*60
+# (date(1970, 1, 1) - date(1900, 1, 1)).days * 24*60*60
+NTP_DELTA = 3155673600 if gmtime(0)[0] == 2000 else 2208988800
+
+# The NTP host can be configured at runtime by doing: ntptime.host = 'myhost.org'
+host = "pool.ntp.org"
+
+def time(hrs_offset=0):  # Local time offset in hrs relative to UTC
+    NTP_QUERY = bytearray(48)
+    NTP_QUERY[0] = 0x1B
+    addr = socket.getaddrinfo(host, 123)[0][-1]
+    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+    poller = select.poll()
+    poller.register(s, select.POLLIN)
+    s.sendto(NTP_QUERY, addr)
+    if poller.poll(1000):  # time in milliseconds
+        msg = s.recv(48)
+        s.close()
+        val = struct.unpack("!I", msg[40:44])[0]
+        return val - NTP_DELTA + hrs_offset * 3600
+    s.close()  # Timeout occurred
+    return 0