Fix wrong return code value, handling and documentation

Change-Id: I17432eb345dd3104b18f32ef8b643968c69371b8
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: Karsten Heimrich <karsten.heimrich@qt.io>

3 files changed, 14 insertions, 10 deletions

diff --git a/src/knx/netip/qknxnetip.cpp b/src/knx/netip/qknxnetip.cpp
index 15d8d38..3ce85f3 100644
--- a/src/knx/netip/qknxnetip.cpp
+++ b/src/knx/netip/qknxnetip.cpp
@@ -512,11 +512,11 @@ bool QKnxNetIp::isCapability(Capability capability)
     This enum describes the possible error codes returned by the remote cEMI
     server after cEMI function properties service requests.
 
+    A return code larger than \c NoError indicates the negative result of the
+    function.
+
     \value NoError The function was successfully executed. The return code
                    indicates the positive result of the function.
-    \value Error   The function was not successfully executed. The return code
-                   indicates the negative result of the function. Can be any
-                   number larger than \c NoError.
 */
 
 /*!
diff --git a/src/knx/netip/qknxnetip.h b/src/knx/netip/qknxnetip.h
index b65e8a1..b806d2c 100644
--- a/src/knx/netip/qknxnetip.h
+++ b/src/knx/netip/qknxnetip.h
@@ -221,8 +221,7 @@ namespace QKnx
 
             enum class ReturnCode : quint8
             {
-                NoError = 0x00,
-                Error = 0x01
+                NoError = 0x00
             };
             Q_ENUM_NS(ReturnCode)
 
diff --git a/src/knx/qknxdevicemanagementframe.cpp b/src/knx/qknxdevicemanagementframe.cpp
index 4defe11..43f9df9 100644
--- a/src/knx/qknxdevicemanagementframe.cpp
+++ b/src/knx/qknxdevicemanagementframe.cpp
@@ -447,9 +447,13 @@ void QKnxDeviceManagementFrame::setError(QKnxNetIpCemiServer::Error error)
 /*!
     Returns the code set by the cEMI server after a cEMI function property
     service request if the frame is a \l FunctionPropertyCommandConfirmation
-    or \l FunctionPropertyStateReadConfirmation frame.
+    or \l FunctionPropertyStateReadConfirmation and is also not a negative
+    confirmation. Otherwise returns \c NoError.
 
-    In all other cases, the function returns the error code stored in the frame.
+    \note A return code larger than \c NoError indicates the negative result of
+    a function property command or function property state read execution.
+
+    \sa data(), isNegativeConfirmation()
 */
 QKnxNetIpCemiServer::ReturnCode QKnxDeviceManagementFrame::returnCode() const
 {
@@ -461,12 +465,13 @@ QKnxNetIpCemiServer::ReturnCode QKnxDeviceManagementFrame::returnCode() const
     default:
         break;
     }
-    return QKnxNetIpCemiServer::ReturnCode::Error;
+    return QKnxNetIpCemiServer::ReturnCode::NoError;
 }
 
 /*!
-    Returns the \a code set by the cEMI server after a cEMI function property
-    service request.
+    Sets the return code stored in the frame to \a code if the frame is a
+    \l FunctionPropertyCommandConfirmation or
+    \l FunctionPropertyStateReadConfirmation frame; does nothing otherwise.
 */
 void QKnxDeviceManagementFrame::setReturnCode(QKnxNetIpCemiServer::ReturnCode code)
 {