Problems trying to specify HDLC

[ThyMYthOS]

Problems trying to specify HDLC

[treiher]

By using the modulo operation in the conditions of the type refinements, the workaround that you described might work:

   type HDLC_Frame is
      message
         -- ...
         Virtual_Control : Control;
         Control : Opaque
            with First => Virtual_Control'First, Size => 8;
         -- ...
      end message;

   for HDLC_Frame use (Control => I_Frame_Control)
      if Virtual_Control mod 2 = 0;

   for HDLC_Frame use (Control => S_Frame_Control)
      if Virtual_Control mod 4 = 1;

   for HDLC_Frame use (Control => U_Frame_Control)
      if Virtual_Control mod 4 = 3;

I also think that for a reasonable specification, the bit order must be configurable. The mechanisms discussed in #1254 could probably be used to specify the type field in the U-frame, but #1254 is still in the design stage.