Add function to read digitizers signal description

Closes #62 (closed)

@lleguy @teichman any suggestions?

src/toolbox_scs/detectors/digitizers.py

@@ -24,6 +24,7 @@ __all__ = [
     'get_laser_peaks',
     'get_peaks',
     'get_tim_peaks',
+    'digitizer_signal_description'
 ]
 
 log = logging.getLogger(__name__)
@@ -986,6 +987,56 @@ def get_digitizer_peaks(run, mnemonics, digitizer, merge_with=None,
     return ds
 
 
+def digitizer_signal_description(run, digitizer=None):
+    """
+    Check for the existence of signal description and return all corresponding
+    channels in a dictionnary.
+    
+    Parameters
+    ----------
+    proposal: int
+        The proposal number
+    runNB: int
+        The run number
+    digitizer: str or list of str (default=None)
+        Name of the digitizer: one in ['FastADC', FastADC2']
+        If None, all digitizers are used
+
+    Returns
+    -------
+    signal_description: dictionnary containing the signal description of
+        the digitizer channels.
+
+
+    Example
+    -------
+    import toolbox_scs as tb
+    run = tb.open_run(3481, 100)
+    signals = tb.digitizer_signal_description(run)
+    signals_fadc2 = tb.digitizer_signal_description(run, 'FastADC2')
+    """
+    if digitizer not in [None, 'FastADC', 'FastADC2']:
+        raise ValueError('digitizer must be one in '
+                         '["FastADC", "FastADC2"]')
+    if digitizer is None:
+        digitizer = ['FastADC', 'FastADC2']
+    else:
+        digitizer = [digitizer]
+    sources = {'FastADC': 'SCS_UTC1_MCP/ADC/1',
+               'FastADC2': 'SCS_UTC2_FADC/ADC/1'}
+    key = 'channel_0.signalDescription.value'
+    res = {}
+    for d in digitizer:
+        if key not in run.get_run_values(sources[d]):
+            raise ValueError('No signal description available for'
+                             f'{d}: {sources[d]}')
+        for ch in range(10):
+            desc = run.get_run_value(sources[d],
+                                     f'channel_{ch}.signalDescription.value')
+            res[f'{d}_Ch{ch}'] = desc
+    return res
+
+
 def calibrateTIM(data, rollingWindow=200, mcp=1, plot=False, use_apd=True, intstart=None,
                  intstop=None, bkgstart=None, bkgstop=None, t_offset=None, npulses_apd=None):
     ''' Calibrate TIM signal (Peak-integrated signal) to the slow ion signal of SCS_XGM