About Channel Conversion

[TSSkyhits]

I try to read the conversion detail of one data channel, which contains a value table.
What I read from the mf4 file via the lib:

As shown in the above figure, only the numerical table can be seen, and the corresponding string list cannot be seen.

This is a value table seen from another tool.

[ihedvall]

@TSSkyhits
Sorry about the design. The IChannelConversion class is just a facade against a CC4Block or a CC3Block class. The MDF version 3 and 4, uses different way of storing. A conversion block consist of a list of floating point values but it can optionally hold a list of links to TX blocks called references.

The trick is that the reference_list_ is actually implemented in the Cc4Block class and is reached by calling the IChannelConversion::NofReferences() followed by one or more calls to the IChannelConversion::Reference(index) that returns a string.

I don't see what type of conversion the block is doing but I assume that it is a value-to-text conversion also known as an enumerate value. In the above example, it should be 5 look-up values and 6 reference (string) values.

The MDF 3 storage is more user friendly while MDF 4 is more flexible. The documentation could have been better or/and the users interface could be better.

You can use the MDF Viewer application which you can download from the latest revision in the GitHub:Ihedvall/mdflib repository. Below a typical enumerate value.

[TSSkyhits]

I successfully read the value table by calling IChannelConversion::NofReferences() and IChannelConversion::Reference(index). Thanks for your suggestion.
There is another question: how to set the IChannelConversion attributes when create a new channel if the signal is enum value type?

[ihedvall]

Simple example

void MostConfigAdapter::CreateCompleteAckChannel(IChannel& parent_channel,
                                               uint32_t byte_offset) const {
  std::ostringstream name;
  name << parent_channel.Name() << ".CAck";

  if (IChannel* c_ack = CreateBitsChannel(parent_channel, name.str(),
                                       byte_offset,0, 3);
      c_ack != nullptr) {
    c_ack->Flags(CnFlag::BusEvent | CnFlag::RangeValid);
    c_ack->Range(0,4);
    if (auto* cc_ack = c_ack->CreateChannelConversion();
        cc_ack != nullptr) {
      cc_ack->Type(ConversionType::ValueToText);
      cc_ack->Name("CompleteAckEnum");
      cc_ack->Parameter(0, 0.0);
      cc_ack->Parameter(1, 1.0);
      cc_ack->Parameter(2, 4.0);
      cc_ack->Reference(0, "No Response");
      cc_ack->Reference(1, "CRC Error");
      cc_ack->Reference(2, "OK");
      cc_ack->Reference(3, "Unknown"); // Default text

      CcComment cc_comment("Complete ACK Enumerate");
      cc_ack->SetCcComment(cc_comment);
    }
  }
}

[TSSkyhits]

CreateBitsChannel: is this a user defined upper layer API? I can not find this API in mdflib.

[TSSkyhits]

If the conversion type is ValueRangeToText, Is there interface to input the value range?
Sample code: cc_ack->Parameter(0, 0.0) can only input one value.

[ihedvall]

@TSSkyhits
No there is not any nice adapter class for this. There is a lot of strange conversions within the CC block and MDF 3 and 4 have totally different design internally.

The Value Range To Text conversion is rarely used. The conversion is P(n+1) > P(n) -> Ref(n/2) i.e. 2 parameters per text string.

The Value to Text conversion is P(n) ->Ref(n) is the normal value to text (enumerate) conversion. It is a very common signal in DBC files.

[TSSkyhits]

I see, thanks!

[ihedvall]

@TSSkyhits
The new style to create data group configuration is to use the IConfigAdapter class. All bus configurations inherit from this adapter class. It is recommended that an end-user application do the same. This base class have some support functions as above. These function are just a wrapper around the create channel and groups functions.

Currently there are basic support function targeted bus configuration that uses a lot of composite sub-channels. If you see that your application uses a lot of repeated code, it could be better to add it to the IConfigAdapter class. Note that this interface was added recently and simplifies the readability of the code and simplify the task of doing the configuration that can be complicated.

[TSSkyhits]

Thanks a lot