JunoEnergyInstrument: Provide INSTANTANEOUS interface

This allows clients to use the instrument more easily from their code
if they were previously used to using an HWMON-style interface.

In order to provide the measurement, the existing readenergy binary
is updated and changed so that if no output option is specified then
we just print the current values and exit.

Signed-off-by: Chris Redpath <chris.redpath@arm.com>

devlib/platform/arm.py

@@ -20,7 +20,7 @@ import time
 import pexpect
 
 from devlib.platform import Platform
-from devlib.instrument import Instrument, InstrumentChannel, MeasurementsCsv, CONTINUOUS
+from devlib.instrument import Instrument, InstrumentChannel, MeasurementsCsv, Measurement,  CONTINUOUS,  INSTANTANEOUS
 from devlib.exception import TargetError, HostError
 from devlib.host import PACKAGE_BIN_DIRECTORY
 from devlib.utils.serial_port import open_serial_connection
@@ -208,7 +208,7 @@ class TC2(VersatileExpressPlatform):
 class JunoEnergyInstrument(Instrument):
 
     binname = 'readenergy'
-    mode = CONTINUOUS
+    mode = CONTINUOUS | INSTANTANEOUS
 
     _channels = [
         InstrumentChannel('sys_curr', 'sys', 'current'),
@@ -238,6 +238,7 @@ class JunoEnergyInstrument(Instrument):
             self.channels[chan.name] = chan
         self.on_target_file = self.target.tempfile('energy', '.csv')
         self.command = '{} -o {}'.format(self.binary, self.on_target_file)
+        self.command2 = '{}'.format(self.binary)
 
     def setup(self):
         self.binary = self.target.install(os.path.join(PACKAGE_BIN_DIRECTORY,
@@ -281,4 +282,16 @@ class JunoEnergyInstrument(Instrument):
 
         return MeasurementsCsv(output_file, self.active_channels)
 
+    def take_measurement(self):
+        result = []
+        output = self.target.execute(self.command2).split()
+        reader=csv.reader(output)
+        headings=reader.next()
+        values = reader.next()
+        for chan in self.active_channels:
+            value = values[headings.index(chan.name)]
+            result.append(Measurement(value, chan))
+        print result
+        return result
+