path         = ? Any unix-like path ? ;
port         = "com1" | "com2" | "bootrom" ;
stdioBackend = "stdio" , ";" , port ;
fileBackend  = "file" , ";" , port , ";" , path ;
nmdmBackend  = "nmdm" , ";" , port ;
ttyBackend   = stdioBackend | fileBackend | nmdmBackend ;

Examples:
  stdio;com1
  file;bootrom;/tmp/xyz
  nmdm;com2
