Variable message id length without lenght field

[mathisloge]

Hi Alex,

sorry, I need to ask one more question as I can't really figure that out.
The visca protocol has message Ids that can have variable long message ids, without a size or lenght field.
I wanted to use it like that:

<enum name="ReturnId" type="uint32" length="3" availableLengthLimit="true" semanticType="messageId">
            <validValue name="Ack" val="0x41" />
            <validValue name="Completion" val="0x51" />
            <validValue name="SyntaxError" val="0x6002" />
            <validValue name="CommandNotExecutable" val="0x6141" />
            <validValue name="PanTiltPosInq" val="0x50" />
</enum>
...
 <frame name="CameraFrame">
        <layers>
            <value name="CameraId" interfaces="CommandInterface">
                <interfaceFieldName value="CameraId" />
                <field>
                    <int reuse="CameraId" serOffset="0x8F" />
                </field>
            </value>
            <id name="ReturnCommand" field="ReturnId" />
            <payload name="Command" />
            <checksum name="FrameEnd" alg="custom" algName="EnforceFrameEnd" from="CameraId">
                <int name="FrameEndField" type="uint8" />
            </checksum>
        </layers>
    </frame>

With that it will correctly create the expected byte sequence, however the deserialization to the message object fails.
Do you have an idea on how to do that?

[arobenko]

Hi Mathis,
I don't really know anything about VISCA protocol and it would have been nice if you could attach or provide a link to the protocol specification you're using. I found this one online. I must say the specification is very confusing. If I were you I would use single (0x6Z) byte indicating error message while having type of error to be an <enum> field in the message payload.

<enum name="ReturnId" type="uint8"  semanticType="messageId">
            ...
            <validValue name="ErrorSock0" val="0x60" />
            <validValue name="ErrorSock1" val="0x61" />
            ...
</enum>

<enum name="ErrorType" type="uint8">
    <validValue name="LengthError" val="0x01" />
    <validValue name="SyntaxError" val="0x02" />
    ...
</enum>

<message name="ErrorSock0" id="ReturnId.ErrorSock0">
    <ref field="ErrorType">
</message>

<message name="ErrorSock1" id="ReturnId.ErrorSock1" copyFieldsFrom="ErrorSock0" />

Hope it helps and works for you.