feat: make OpenDTU poll interval and HTTP retries configurable

The mainloop is single threaded and fetches every inverter separately and
synchronously, so poll rate and retry count decide how long dbus method calls
on the service stay unanswered: worst case = inverters x tries x HTTPTimeout.

With five inverters, three tries and HTTPTimeout=1.5 that is 27.5s. A DTU that
turns sluggish therefore blocks the mainloop long enough for GetValue callers
to run into org.freedesktop.DBus.Error.NoReply, while svstat and the log still
look healthy because values keep being published.

Both values were hardcoded. They now come from config.ini as
OpenDTUPollingIntervall and MaxFetchTries, defaulting to the previous 5000ms
and 3 tries, so existing setups are unaffected.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: dsteinkopf

README.md

@@ -123,6 +123,8 @@ Within the project there is a file `/data/dbus-opendtu/config.ini`. Most importa
 | NumberOfInvertersToQuery | Number of Inverters to query. Set a value larger than "0" when not all inverters should be considered. \*1                                                                            |
 | useYieldDay              | send YieldDay instead of YieldTotal. Set this to 1 to prevent VRM from adding the total value to the history on one day. E.g. if you don't start using the inverter at 0.             |
 | ESP8266PollingIntervall  | For ESP8266 reduce polling intervall to reduce load, default 10000ms                                                                                                                  |
+| OpenDTUPollingIntervall  | How often an OpenDTU is polled, in ms. Raise this if the DTU gets slow with many inverters. Default: 5000ms                                                                            |
+| MaxFetchTries            | How often a failed HTTP call is attempted before the value is dropped. Every attempt blocks the mainloop for up to HTTPTimeout, so lowering this keeps the dbus service responsive while the DTU is slow. Default: 3 |
 | Logging                  | Valid options for log level: CRITICAL, ERROR, WARNING, INFO, DEBUG, NOTSET, to keep logfile small use ERROR or CRITICAL                                                               |
 | MaxAgeTsLastSuccess      | Maximum accepted age of ts_last_success in Ahoy status message. If ts_last_success is older than this number of seconds, values are not used. Set this to < 0 to disable this check.  |
 | DryRun                   | Set this to a value different to "0" to prevent values from being sent. Use this for debugging or experiments.                                                                        |

config.example

@@ -19,6 +19,14 @@ useYieldDay=0
 #For ESP8266 reduce polling intervall to reduce load
 ESP8266PollingIntervall=10000
 
+#How often an OpenDTU is polled, in ms. Raise this if the DTU gets slow with many inverters.
+OpenDTUPollingIntervall=5000
+
+#How often a failed HTTP call is attempted before the value is dropped.
+#Every attempt blocks the mainloop for up to HTTPTimeout, so lowering this keeps the dbus
+#service responsive while the DTU is slow, at the price of losing a reading now and then.
+MaxFetchTries=3
+
 #Possible Options for Log Level: CRITICAL, ERROR, WARNING, INFO, DEBUG, NOTSET
 #To keep current.log small use ERROR
 Logging=ERROR

dbus_service.py

@@ -220,6 +220,13 @@ def _read_config_dtu(self, actual_inverter):
 
         self.dry_run = is_true(get_default_config(config, "DryRun", False))
         self.pollinginterval = int(get_config_value(config, "ESP8266PollingIntervall", "DEFAULT", "", 10000))
+        # The mainloop is single threaded and fetches every inverter separately and
+        # synchronously, so poll rate and retry count decide how long dbus method calls on this
+        # service stay unanswered: worst case = inverters x tries x HTTPTimeout. With five
+        # inverters, three tries and a 1.5s timeout that is 27.5s - long enough for GetValue
+        # callers to run into org.freedesktop.DBus.Error.NoReply while the DTU is slow.
+        self.opendtu_polling_interval = int(get_config_value(config, "OpenDTUPollingIntervall", "DEFAULT", "", 5000))
+        self.max_fetch_tries = int(get_config_value(config, "MaxFetchTries", "DEFAULT", "", 3))
         self.meter_data = 0
         self.httptimeout = get_default_config(config, "HTTPTimeout", 2.5)
         self._load_error_handling_config(config)
@@ -352,7 +359,7 @@ def _get_polling_interval(self):
                 polling_interval = 5000
 
         elif self.dtuvariant == constants.DTUVARIANT_OPENDTU:
-            polling_interval = 5000
+            polling_interval = self.opendtu_polling_interval
 
         elif self.dtuvariant == constants.DTUVARIANT_TEMPLATE:
             polling_interval = self.pollinginterval
@@ -493,8 +500,8 @@ def fetch_url(self, url, try_number=1):
                                  f"status={json_str.status_code},\nresponse={json_str.text}")
             return json
         except Exception:
-            # retry same call up to 3 times
-            if try_number < 3:  # pylint: disable=no-else-return
+            # retry same call up to MaxFetchTries times
+            if try_number < self.max_fetch_tries:  # pylint: disable=no-else-return
                 time.sleep(0.5)
                 return self.fetch_url(url, try_number + 1)
             else: