Modified the behaviour of pycboard for transferring device driver fil…

…es to pyboard. New behaviour is:

- When a task file or hardware definition file is transferred to the pyboard,  the required device driver files are tranferred unless they are already on the board and have the same file hash.

- When the framework is reloaded the devices folder on the pyboard is reset, by deleting all device driver files and rebuilding the device_file2class dictionary.

com/pycboard.py

@@ -64,7 +64,7 @@ def __init__(self, serial_port,  baudrate=115200, verbose=True, print_func=print
         self.print = print_func        # Function used for print statements.
         self.data_logger = data_logger # Instance of Data_logger class for saving and printing data.
         self.status = {'serial': None, 'framework':None, 'usb_mode':None}
-        self.device_files_on_pyboard = [] # List of files in devices folder on pyboard.
+        self.device_files_on_pyboard = {} # Dict {file_name:file_hash} of files in devices folder on pyboard.
         if not Pycboard.device_class2file: # Scan devices folder to find files where device classes are defined.
             self.make_device_class2file_map()
         try:    
@@ -109,7 +109,7 @@ def reset(self):
         try:
             self.exec('from pyControl import *; import devices')
             self.status['framework'] = True # Framework imported OK.
-            self.device_files_on_pyboard = self.get_folder_contents('devices')
+            self.device_files_on_pyboard = self.get_folder_contents('devices', get_hash=True)
         except PyboardError as e:
             error_message = e.args[2].decode()
             if (("ImportError: no module named 'pyControl'" in error_message) or
@@ -260,19 +260,27 @@ def remove_file(self, file_path):
         except PyboardError:
             pass # File does not exist.
 
-    def get_folder_contents(self, folder_path):
-        '''Get a list of the files in a folder on the pyboard.'''
-        return eval(self.eval('os.listdir({})'.format(repr(folder_path))).decode())
+    def get_folder_contents(self, folder_path, get_hash=False):
+        '''Get a list of the files in a folder on the pyboard, if
+        get_hash=True a dict {file_name:file_hash} is returned instead'''
+        file_list = eval(self.eval('os.listdir({})'.format(repr(folder_path))).decode())
+        if get_hash:
+            return {file_name: self.get_file_hash(folder_path+'/'+file_name)
+                    for file_name in file_list}
+        else:    
+            return file_list
 
     # ------------------------------------------------------------------------------------
     # pyControl operations.
     # ------------------------------------------------------------------------------------
 
     def load_framework(self):
-        '''Copy the pyControl framework folder to the board.'''
+        '''Copy the pyControl framework folder to the board, reset the devices folder
+        on pyboard by removing all devices files, and rebuild the device_class2file dict.'''
         self.print('\nTransferring pyControl framework to pyboard.', end='')
         self.transfer_folder(dirs['framework'], file_type='py', show_progress=True)
-        self.transfer_folder(dirs['devices'], files=['__init__.py'], remove_files=False, show_progress=True)
+        self.transfer_folder(dirs['devices'], files=['__init__.py'], remove_files=True, show_progress=True)
+        self.make_device_class2file_map()
         error_message = self.reset()
         if not self.status['framework']:
             self.print('\nError importing framework:')
@@ -282,12 +290,9 @@ def load_framework(self):
         return 
 
     def load_hardware_definition(self, hwd_path=os.path.join(dirs['config'], 'hardware_definition.py')):
-        '''Transfer a hardware definition file to pyboard.  Device driver files needed for
-        the hardware definition are transferred to the pyboard and any other device driver
-        files on the pyboard are deleted.'''
+        '''Transfer a hardware definition file to pyboard.'''
         if os.path.exists(hwd_path):
-            self.make_device_class2file_map()
-            self.transfer_device_files(hwd_path, reset_folder=True)
+            self.transfer_device_files(hwd_path)
             self.print('\nTransferring hardware definition to pyboard.', end='')
             self.transfer_file(hwd_path, target_path='hardware_definition.py')
             self.reset()
@@ -301,35 +306,37 @@ def load_hardware_definition(self, hwd_path=os.path.join(dirs['config'], 'hardwa
         else:
             self.print('Hardware definition file not found.')
 
-    def transfer_device_files(self, ref_file_path, reset_folder=False, return_filenames=False):
-        '''Transfer device driver files defining classes used in ref_file to the pyboard devices folder. 
-        If reset_folder=True then any files not used by ref_file are deleted from the pyboard filesystem, 
-        and any files that have changed on the computer are retransferred.  If reset_folder=False then
-        only files that are not already on the pyboard filesystem are transferred. If return_filenames=True
-        then no files are transferred but a list of the filenames used in ref_file is returned.'''
+    def transfer_device_files(self, ref_file_path):
+        '''Transfer device driver files defining classes used in ref_file to the pyboard devices folder.
+        Driver file that are already on the pyboard are only be transferred if they have changed
+        on the computer.'''
+        used_device_files = self._get_used_device_files(ref_file_path)
+        files_to_transfer = []
+        for device_file in used_device_files: # File not on pyboard.
+            if device_file not in self.device_files_on_pyboard.keys():
+                files_to_transfer.append(device_file)
+            else: 
+                file_hash = _djb2_file(os.path.join(dirs['devices'],device_file))
+                if file_hash != self.device_files_on_pyboard[device_file]: # File has changed.
+                    files_to_transfer.append(device_file)
+        if files_to_transfer:
+                self.print(f'\nTransfering device driver files {files_to_transfer} to pyboard', end='')
+                self.transfer_folder(dirs['devices'], files=files_to_transfer, remove_files=False, show_progress=True)
+                self.reset()
+                self.print(' OK')
+
+    def _get_used_device_files(self, ref_file_path):
+        '''Return a list of device driver file names containing device classes used in ref_file'''
         ref_file_name = os.path.split(ref_file_path)[-1]
         with open(ref_file_path, 'r') as f:
             file_content = f.read()
-        device_files = [Pycboard.device_class2file[device_class] for device_class in 
-                        Pycboard.device_class2file.keys() if device_class in file_content
-                        and not ref_file_name == Pycboard.device_class2file[device_class]]
+        device_files = [device_file for device_class, device_file in Pycboard.device_class2file.items()
+                        if device_class in file_content and not ref_file_name == device_file]
         # Add any device driver files containing classes used in device_files.
         for device_file in device_files.copy():
-            device_files += self.transfer_device_files(os.path.join(dirs['devices'], device_file), return_filenames=True)
+            device_files += self._get_used_device_files(os.path.join(dirs['devices'], device_file))
         device_files = list(set(device_files)) # Remove duplicates.
-        if return_filenames:
-            return device_files
-        else:
-            if reset_folder: 
-                device_files += ['__init__.py']
-            else:
-                device_files = list(set(device_files)-set(self.device_files_on_pyboard))
-            if device_files:
-                self.print(f'\nTransfering device driver files {device_files} to pyboard', end='')
-                self.transfer_folder(dirs['devices'], files=device_files, remove_files=reset_folder, show_progress=True)
-                self.reset()
-                self.print(' OK')
-
+        return device_files
 
     def make_device_class2file_map(self):
         '''Make dict mapping device class names to file in devices folder containing