Fix unhandled CME error code 0 and update docs

Fixes #8

Signed-off-by: Gregers Gram Rygg <[email protected]>

Author: gregersrygg

README.md

@@ -80,6 +80,9 @@ usage: nrfcredstore [--baudrate BAUDRATE] [--timeout TIMEOUT] dev delete SECURE_
 
 ### generate subcommand
 
+> [!IMPORTANT]
+> This command requires modem firmware version greater than or equal to 1.3.0.
+
 Generate a private key in the modem and output a certificate signing request.
 
 ```

src/nrfcredstore/at_client.py

@@ -1,6 +1,7 @@
 from nrfcredstore.exceptions import ATCommandError, NoATClientException
 
 ERR_CODE_TO_MSG = {
+    0:   'AT command not supported by firmware version. Upgrade modem firmware?',
     513: 'Not found',
     514: 'Not allowed',
     515: 'Memory full',

tests/test_at_client.py

@@ -38,6 +38,10 @@ def error_resp(self, at_client):
     def error_code_resp(self, at_client):
         self.serial.readline.return_value = '+CME ERROR: 514\r\n'.encode('utf-8')
 
+    @pytest.fixture
+    def error_code_0_resp(self, at_client):
+        self.serial.readline.return_value = '+CME ERROR: 0\r\n'.encode('utf-8')
+
     @pytest.fixture
     def error_ok_resp(self, at_client):
         self.serial.readline.side_effect = [b'ERROR', b'OK']
@@ -110,6 +114,11 @@ def test_at_command_error_code_maps_to_message(self, at_client, error_code_resp)
             at_client.at_command('AT')
         assert 'Not allowed' in str(excinfo.value)
 
+    def test_unsupported_cmd_error_code(self, at_client, error_code_0_resp):
+        with pytest.raises(ATCommandError) as excinfo:
+            at_client.at_command('AT')
+        assert 'AT command not supported by firmware version' in str(excinfo.value)
+
     def test_at_command_with_single_line_response(self, at_client):
         self.serial.readline.side_effect = [b'single', b'OK']
         assert at_client.at_command('AT+CGSN') == ['single']