[cleoo]

What is the difference between the boundary conditions (for temperature) fixedValue and total Temperature, i consulted the user guide but the explanation was very basic: This boundary condition provides a total temperature condition

[Bloerb]

This should answer your question about total temperature:
https://en.wikipedia.org/wiki/Stagnation_temperature

And this is the actual implementation in the code:

    const fvPatchVectorField& Up =
        patch().lookupPatchField<volVectorField, vector>(UName_);

    const fvsPatchField<scalar>& phip =
        patch().lookupPatchField<surfaceScalarField, scalar>(phiName_);

    const fvPatchField<scalar>& psip =
        patch().lookupPatchField<volScalarField, scalar>(psiName_);

    scalar gM1ByG = (gamma_ - 1.0)/gamma_;

    operator==
    (
        T0_/(1.0 + 0.5*psip*gM1ByG*(1.0 - pos(phip))*magSqr(Up))
    );

operator is the temperature at the wall. Which is T0 devided by the rest. pos is zero when the value for phi is negative.