Implement the ClearOverrunCounterAndFlag sub-function code.

Even if machine specific, we can implement it software side;
as our server can and should be a total of all available and
documented functionality as described by the Modbus specs.

Change-Id: I97b9eb8f6495b6ce9c2a858d22326f236d9b044b
Reviewed-by: Alex Blasche <alexander.blasche@theqtcompany.com>

3 files changed, 18 insertions, 8 deletions

diff --git a/src/serialbus/qmodbus_symbols_p.h b/src/serialbus/qmodbus_symbols_p.h
index 6ffc938..20ec329 100644
--- a/src/serialbus/qmodbus_symbols_p.h
+++ b/src/serialbus/qmodbus_symbols_p.h
@@ -69,14 +69,8 @@ enum SubFunctionCode {
     ReturnServerNoResponseCount = 0x000f,
     ReturnServerNAKCount = 0x0010,
     ReturnServerBusyCount = 0x0011,
-    ReturnBusCharacterOverrunCount = 0x0012
-
-    // The Clear Overrun Counter and Flag handling for diagnostics
-    // sub-code is only used in the legacy Modicon 84 and 884 PLC
-    // processor system where it clears the only counter there (the
-    // IOP Overrun counter which doesn't exist anywhere else) and
-    // the according overrun flag bit 0 in the diagnosticRegister.
-    // ClearOverrunCounterAndFlag = 0x0014 // Deliberately not implemented!
+    ReturnBusCharacterOverrunCount = 0x0012,
+    ClearOverrunCounterAndFlag = 0x0014
 };
 
 }
diff --git a/src/serialbus/qmodbusserver.cpp b/src/serialbus/qmodbusserver.cpp
index 20ddec7..f3a5a58 100644
--- a/src/serialbus/qmodbusserver.cpp
+++ b/src/serialbus/qmodbusserver.cpp
@@ -894,6 +894,14 @@ QModbusResponse QModbusServerPrivate::processDiagnosticsRequest(const QModbusReq
         CHECK_SIZE_AND_CONDITION(request, (data != 0x0000));
         return QModbusResponse(request.functionCode(), subFunctionCode,
                                m_counters[static_cast<Counter> (subFunctionCode)]);
+
+    case Diagnostics::ClearOverrunCounterAndFlag: {
+        CHECK_SIZE_AND_CONDITION(request, (data != 0x0000));
+        m_counters[Diagnostics::ReturnBusCharacterOverrunCount] = 0;
+        quint16 reg = q_func()->value(QModbusServer::DiagnosticRegister).value<quint16>();
+        q_func()->setValue(QModbusServer::DiagnosticRegister, reg &~ 1); // clear first bit
+        return QModbusResponse(request.functionCode(), request.data());
+    }
     }
     return QModbusExceptionResponse(request.functionCode(),
         QModbusExceptionResponse::IllegalFunction);
diff --git a/tests/auto/qmodbusserver/tst_qmodbusserver.cpp b/tests/auto/qmodbusserver/tst_qmodbusserver.cpp
index 09abdd3..6c3d844 100644
--- a/tests/auto/qmodbusserver/tst_qmodbusserver.cpp
+++ b/tests/auto/qmodbusserver/tst_qmodbusserver.cpp
@@ -1189,6 +1189,14 @@ private slots:
         QCOMPARE(local.setValue(QModbusServer::ListenOnlyMode, true), true);
         QCOMPARE(local.value(QModbusServer::ListenOnlyMode).toBool(), true);
     }
+
+    void testClearOverrunCounterAndFlag()
+    {
+        TestServer server;
+        server.setValue(QModbusServer::DiagnosticRegister, 0xffff);
+        server.processRequest(QModbusRequest(QModbusRequest::Diagnostics, quint16(0x0014), quint16(0)));
+        QCOMPARE(server.value(QModbusServer::DiagnosticRegister).value<quint16>(), quint16(0xfffe));
+    }
 };
 
 QTEST_MAIN(tst_QModbusServer)