`Vgmn`::
 * Mandatory arguments:
   * `instance name`
 * Optional arguments:
   * `min_latency`
 * Example:
      * my_vgmn = Vgmn("my_vgmn", 10)

 `Xcache`::
 * Mandatory arguments:
   * `instance name`
 * Optional arguments:
   * `dcache_lines` : number of lines in data cache
   * `dcache_words` : number of words per line in data cache
   * `icache_lines` : number of lines in instruction cache
   * `icache_words` : number of words per line in instruction cache
 * Example:
    * my_cache = Xcache("my_cache", dcache_lines = 32, dcache_words = 8, icache_lines = 32, icache_words = 8)

 `Mips`::
 * Mandatory arguments:
     * `name`

 `MultiRam`
 * Mandatory arguments:
   * `name`
 * Optional arguments:
   * a list of segments, allocated with Segment()
 * Example:
   * my_ram = MultiRam("my_ram", seg1, seg2, seg3)

 `MultiTty`
 * Mandatory arguments:
   * `name`