Gramatical layer

It's rather simple. Start symbol of grammar is 'call':

     call -> ('c' | 'v' | 'r') number 'k' command arglist

     arglist -> /* empty */ 
              | arglist arg

     arg -> ('k' | 'i' | 's') data
    
So nothing complicated here. First word of call describes its length, then the command follows. Command describes what to do with arguments.