Fix a couple problems.

- Fail example scripts if an exception is raised at any point.
- Rework `_crc_add` to produce a reliable CRC. This requires us to rely more on
string manipulation and less on python dicts. Prior to this commit, the CRC was
computed over the string representation of the request (via `json.dumps`) and
then it was added to the request dict. Then, when it was time to serialize the
request for transmission and we converted the dict to a string again, because
the CRC field had been added, the order of the fields changed and the CRC was
invalidated. This is because Python dicts are fundamentally unordered
collections.
- Add missing timeout reset to `OpenSerial`'s `receive` method.
- Increase cpy_example.py UART RX buffer size. I was seeing the end of responses
get cut off with the default size (64). Increased to 128.

examples/notecard-basics/cpy_example.py

@@ -14,20 +14,6 @@
 import busio  # noqa: E402
 
 
-def NotecardExceptionInfo(exception):
-    """Construct a formatted Exception string.
-
-    Args:
-        exception (Exception): An exception object.
-
-    Returns:
-        string: a summary of the exception with line number and details.
-    """
-    name = exception.__class__.__name__
-    return sys.platform + ": " + name \
-        + ": " + " ".join(map(str, exception.args))
-
-
 def configure_notecard(card, product_uid):
     """Submit a simple JSON-based request to the Notecard.
 
@@ -39,11 +25,7 @@ def configure_notecard(card, product_uid):
     req["product"] = product_uid
     req["mode"] = "continuous"
 
-    try:
-        card.Transaction(req)
-    except Exception as exception:
-        print("Transaction error: " + NotecardExceptionInfo(exception))
-        time.sleep(5)
+    card.Transaction(req)
 
 
 def get_temp_and_voltage(card):
@@ -53,20 +35,13 @@ def get_temp_and_voltage(card):
         card (object): An instance of the Notecard class
 
     """
-    temp = 0
-    voltage = 0
-
-    try:
-        req = {"req": "card.temp"}
-        rsp = card.Transaction(req)
-        temp = rsp["value"]
+    req = {"req": "card.temp"}
+    rsp = card.Transaction(req)
+    temp = rsp["value"]
 
-        req = {"req": "card.voltage"}
-        rsp = card.Transaction(req)
-        voltage = rsp["value"]
-    except Exception as exception:
-        print("Transaction error: " + NotecardExceptionInfo(exception))
-        time.sleep(5)
+    req = {"req": "card.voltage"}
+    rsp = card.Transaction(req)
+    voltage = rsp["value"]
 
     return temp, voltage
 
@@ -75,7 +50,8 @@ def run_example(product_uid, use_uart=True):
     """Connect to Notcard and run a transaction test."""
     print("Opening port...")
     if use_uart:
-        port = busio.UART(board.TX, board.RX, baudrate=9600)
+        port = busio.UART(board.TX, board.RX, baudrate=9600,
+                          receiver_buffer_size=128)
     else:
         port = busio.I2C(board.SCL, board.SDA)
 

examples/notecard-basics/mpy_example.py

@@ -16,20 +16,6 @@
 from machine import Pin
 
 
-def NotecardExceptionInfo(exception):
-    """Construct a formatted Exception string.
-
-    Args:
-        exception (Exception): An exception object.
-
-    Returns:
-        string: a summary of the exception with line number and details.
-    """
-    name = exception.__class__.__name__
-    return sys.platform + ": " + name + ": " \
-        + " ".join(map(str, exception.args))
-
-
 def configure_notecard(card, product_uid):
     """Submit a simple JSON-based request to the Notecard.
 
@@ -41,11 +27,7 @@ def configure_notecard(card, product_uid):
     req["product"] = product_uid
     req["mode"] = "continuous"
 
-    try:
-        card.Transaction(req)
-    except Exception as exception:
-        print("Transaction error: " + NotecardExceptionInfo(exception))
-        time.sleep(5)
+    card.Transaction(req)
 
 
 def get_temp_and_voltage(card):
@@ -55,20 +37,13 @@ def get_temp_and_voltage(card):
         card (object): An instance of the Notecard class
 
     """
-    temp = 0
-    voltage = 0
-
-    try:
-        req = {"req": "card.temp"}
-        rsp = card.Transaction(req)
-        temp = rsp["value"]
-
-        req = {"req": "card.voltage"}
-        rsp = card.Transaction(req)
-        voltage = rsp["value"]
-    except Exception as exception:
-        print("Transaction error: " + NotecardExceptionInfo(exception))
-        time.sleep(5)
+    req = {"req": "card.temp"}
+    rsp = card.Transaction(req)
+    temp = rsp["value"]
+
+    req = {"req": "card.voltage"}
+    rsp = card.Transaction(req)
+    voltage = rsp["value"]
 
     return temp, voltage
 

notecard/notecard.py

@@ -129,7 +129,7 @@ def __init__(self, debug=False):
         self._card_supports_crc = False
         self._reset_required = True
 
-    def _crc_add(self, req, seq_number):
+    def _crc_add(self, req_string, seq_number):
         """Add a CRC field to the request.
 
         The CRC field also contains a sequence number and has this format:
@@ -139,10 +139,18 @@ def _crc_add(self, req, seq_number):
         SSSS is the sequence number encoded as a string of 4 hex digits.
         CCCCCCCC is the CRC32 encoded as a string of 8 hex digits.
         """
-        req_bytes = json.dumps(req, separators=(',', ':')).encode('utf-8')
+        req_bytes = req_string.encode('utf-8')
         crc_hex = '{:08x}'.format(crc32(req_bytes))
         seq_number_hex = '{:04x}'.format(seq_number)
-        req['crc'] = f'{seq_number_hex}:{crc_hex}'
+        crc_field = f'"crc":"{seq_number_hex}:{crc_hex}"'
+        req_string_w_crc = req_string[:-1]
+        if req_string[-2] == '{':
+            req_string_w_crc += f'{crc_field}'
+        else:
+            req_string_w_crc += f',{crc_field}'
+        req_string_w_crc += '}'
+
+        return req_string_w_crc
 
     def _crc_error(self, rsp_bytes):
         """Check the CRC in a Notecard response."""
@@ -199,12 +207,13 @@ def _prepare_request(self, req):
         rsp_expected = 'req' in req
 
         # If this is a request and not a command, add a CRC.
+        req_string = json.dumps(req, separators=(',', ':'))
         if rsp_expected:
-            self._crc_add(req, self._last_request_seq_number)
+            req_string = self._crc_add(req_string,
+                                       self._last_request_seq_number)
 
         # Serialize the JSON request to a string, removing any unnecessary
         # whitespace.
-        req_string = json.dumps(req, separators=(',', ':'))
         if self._debug:
             print(req_string)
 
@@ -320,7 +329,7 @@ def Transaction(self, req, lock=True):
                         if '{io}' in rsp_json['err']:
                             if self._debug:
                                 print(('Response has error field indicating I/O'
-                                       ' error.'))
+                                       f' error: {rsp_json}'))
 
                             error = True
                             retries_left -= 1
@@ -329,8 +338,8 @@ def Transaction(self, req, lock=True):
                         elif '{bad-bin}' in rsp_json['err']:
                             if self._debug:
                                 print(('Response has error field indicating '
-                                       'binary I/O error. Not eligible for '
-                                       'retry.'))
+                                       f'binary I/O error: {rsp_json}'))
+                                print('Not eligible for retry.')
 
                             error = True
                             break
@@ -433,6 +442,7 @@ def receive(self, timeout_secs=CARD_INTRA_TRANSACTION_TIMEOUT_SEC,
                     time.sleep(.001)
 
             timeout_secs = CARD_INTRA_TRANSACTION_TIMEOUT_SEC
+            start = start_timeout()
             byte = self._read_byte()
             data.extend(byte)
             received_newline = byte == b'\n'

test/test_notecard.py

@@ -49,23 +49,25 @@ def test_txn_manager_is_valid_after_pins_set(self):
     # _crc_add tests
     def test_crc_add_adds_a_crc_field(self):
         card = notecard.Notecard()
-        req = {'req': 'hub.status'}
+        req = '{"req":"hub.status"}'
 
-        card._crc_add(req, 0)
+        req_string = card._crc_add(req, 0)
 
-        assert 'crc' in req
+        req_json = json.loads(req_string)
+        assert 'crc' in req_json
 
     def test_crc_add_formats_the_crc_field_correctly(self):
         card = notecard.Notecard()
-        req = {'req': 'hub.status'}
+        req = '{"req":"hub.status"}'
         seq_number = 37
 
-        card._crc_add(req, seq_number)
+        req_string = card._crc_add(req, seq_number)
 
+        req_json = json.loads(req_string)
         # The format should be SSSS:CCCCCCCC, where S and C are hex digits
         # comprising the sequence number and CRC32, respectively.
         pattern = r'^[0-9A-Fa-f]{4}:[0-9A-Fa-f]{8}$'
-        assert re.match(pattern, req['crc'])
+        assert re.match(pattern, req_json['crc'])
 
     # _crc_error tests.
     @pytest.mark.parametrize('crc_supported', [False, True])