Mistake 1
There is a contradiction between the format of (G)ATT commands (page 126) and general commands (page 11), and it turned out that the latter was the correct one. Thus, opcode if followed by the length specifier.
discussion here: http://e2e.ti.com/support/low_power_rf/f/538/p/207743/736020.aspx
Mistake 2
In GAP set parameter command the paramID parameter has the length of 2 bytes according to page 70, but after checking it with btool, it seems to 1 byte long. Probably the same holds for get parameter.
