steplogger: Introduce code to perform data logging

The code is not yet enabled by default but it can be tested by adding
custom code to an interested user's main.py .

Signed-off-by: Daniel Thompson <daniel@redfelineninja.org.uk>

docs/wasp.rst

@@ -38,6 +38,10 @@ System
    :members:
    :undoc-members:
 
+.. automodule:: steplogger
+   :members:
+   :undoc-members:
+
 .. automodule:: widgets
    :members:
 

wasp/boards/manifest_240x240.py

@@ -29,5 +29,6 @@ manifest = (
     'fonts/sans28.py',
     'fonts/sans36.py',
     'icons.py',
+    'steplogger.py',
     'widgets.py',
 )

wasp/steplogger.py

@@ -0,0 +1,96 @@
+# SPDX-License-Identifier: LGPL-3.0-or-later
+# Copyright (C) 2020 Daniel Thompson
+
+"""Step logger
+~~~~~~~~~~~~~~
+
+Capture and record data from the step counter
+"""
+
+import array
+import os
+import time
+import wasp
+
+from micropython import const
+
+TICK_PERIOD = const(6 * 60)
+DUMP_LENGTH = const(5)
+DUMP_PERIOD = const(DUMP_LENGTH * TICK_PERIOD)
+
+class StepLogger:
+    def __init__(self):
+        self._data = array.array('H', (0,) * DUMP_LENGTH)
+        self._steps = wasp.watch.accel.steps
+
+        try:
+            os.mkdir('logs')
+        except:
+            pass
+
+        # Queue a tick
+        self._t = int(wasp.watch.rtc.time()) // TICK_PERIOD * TICK_PERIOD
+        wasp.system.set_alarm(self._t + TICK_PERIOD, self._tick)
+
+    def _tick(self):
+        """Capture the current step count in N minute intervals.
+
+        The samples are queued in a small RAM buffer in order to reduce
+        the number of flash access. The data is written out every few hours
+        in a binary format ready to be reloaded and graphed when it is
+        needed.
+        """
+        t = self._t
+
+        # Work out where we are in the dump period
+        i = t % DUMP_PERIOD // TICK_PERIOD
+
+        # Get the current step count and record it
+        steps = wasp.watch.accel.steps
+        self._data[i] = steps - self._steps 
+        self._steps = steps
+
+        # Queue the next tick
+        wasp.system.set_alarm(t + TICK_PERIOD, self._tick)
+        self._t += TICK_PERIOD
+
+        if i < (DUMP_LENGTH-1):
+            return
+
+        # Record the data in the flash
+        walltime = time.localtime(t)
+        yyyy = walltime[0]
+        mm = walltime[1]
+        dd = walltime[2]
+
+        # Find when (in seconds) "today" started
+        then = int(time.mktime((yyyy, mm, dd, 0, 0, 0, 0, 0, 0)))
+        elapsed = t - then
+
+        # Work out how dumps we expect to find in today's dumpfile
+        dump_num = elapsed // DUMP_PERIOD
+
+        # Update the log data
+        try:
+            os.mkdir('logs/' + str(yyyy))
+        except:
+            pass
+        fname = 'logs/{}/{:02d}-{:02d}.steps'.format(yyyy, mm, dd)
+        offset = dump_num * DUMP_LENGTH * 2
+        try:
+            sz = os.stat(fname)[6]
+        except:
+            sz = 0
+        f = open(fname, 'ab')
+        # This is a portable (between real Python and MicroPython) way to
+        # grow the file to the right size.
+        f.seek(min(sz, offset))
+        for _ in range(sz, offset, 2):
+            f.write(b'\x00\x00')
+        f.write(self._data)
+        f.close()
+
+        # Wipe the data
+        data = self._data
+        for i in range(DUMP_LENGTH):
+            data[i] = 0