experiments9/GUIDELINES.rst

   1
   2
   3 ================================
   4 Quick Guidelines on Floorplaning
   5 ================================
   6
   7
   8 Some hints about how to avoid common pitfall making the floorplan.
   9
  10 Terminology:
  11
  12 * ``Cell`` : Even if in Hurricane it contain both the netlist and
  13   the layout, in this context we will consider it as a pure netlist.
  14
  15 * ``Block`` : The Python class wrapper around a ``Cell`` to change it
  16   into a placed and routed layout used as black box by the above
  17   hierarchical levels. It is both the program that perform the P&R
  18   and a cache for upper levels.
  19     If it contains no sub-blocks, it is placed flat (virtual flatten).
  20
  21
  22 Disclaimer
  23 ==========
  24
  25 At this moment, the Block tools can hardly be called floorplaner.
  26 They provides very basic facility for manual floorplanning.
  27
  28
  29 Layout Caching
  30 ==============
  31
  32 To create a block from a ``Cell``:
  33
  34 .. code-block:: python
  35
  36    add = af.getCell( 'add', CRL.Catalog.State.Views )
  37    blockAdd = Block.create \
  38        ( add
  39        , ioPins=[ (IoPin.SOUTH|IoPin.A_BEGIN, 'a({})', l( 10.0), l(20.0), 16)
  40                 , (IoPin.SOUTH|IoPin.A_BEGIN, 'b({})', l( 20.0), l(20.0), 16)
  41                 , (IoPin.NORTH|IoPin.A_BEGIN, 'o({})', l(100.0), l(10.0), 16)
  42                 ]
  43        )
  44    blockAdd.state.cfg.etesian.spaceMargin = 0.10
  45    blockAdd.state.fixedHeight = l(400)
  46    blockAdd.state.useSpares   = False
  47    blockAdd.state.editor      = editor
  48    rvalue = blockAdd.build()
  49
  50
  51 If you load the ``Cell`` with the flag ``CRL.Catalog.State.Views``, the
  52 parser will attemps to load both the netlist (mandatory) and the layout.
  53 If the layout is present, then the block **will not be P&R again**,
  54 the current layout is reused.
  55
  56 If you want to selectivelely rebuild one block, you can either remove
  57 the relevant ``ap`` file or change the loading flag to:
  58
  59 .. code-block:: python
  60
  61    add = af.getCell( 'add', CRL.Catalog.State.Logical )
  62
  63
  64 Pin Placement
  65 =============
  66
  67 Pin placement is critical both for the P&R of the block and the one
  68 of the above level. So here is some hints.
  69
  70 * Do not pack pin as closely as possible. Try to leave at least one
  71   free pitch between them. Otherwise it may create huge contention
  72   point both inside the block and outside to access the block.
  73
  74 * If there is a *sliced* structure, that is one same treatment is
  75   done for each bit of the I/O busses, interleave the relevant
  76   busses pins. For examle, instead of having: ::
  77
  78     a(0) a(1) a(2) a(3) b(0) b(1) b(2) b(3)
  79
  80   Try: ::
  81
  82     a(0) b(0) a(1) b(1) a(2) b(2) a(3) b(3)
  83
  84
  85 Aspect Ratio (aka Form Factor)
  86 ==============================
  87
  88 It is important to consider that the routing capacity in one direction
  89 is directly proportional to the length of the side of the abutment box
  90 in the perpandicular direction. So, if you make a very *flat* box,
  91 the number of horizontal tracks became limited, and may become not
  92 routable.
  93
  94 This effect is related to the kind of graph of the netlist. If it
  95 has a strong pipeline structure, a very elongated shape may be still
  96 be possible.
  97
  98
  99 The Halo Parameter
 100 ==================
 101
 102 By default, the global router will search to connect all pins of a Net
 103 in the square area defined by the pins, inflated by the halo (the halo
 104 is given in number of GCells, that is the height of a standard cell).
 105 A problem arise if you have a net of only two pins (usually 60% of the
 106 nets are like that), each across of a huge block. To avoid being stuck,
 107 the halo must be increased by at least half the size of the biggest
 108 block dimension. Note that, by drastically increasing the search area
 109 it may slow down much the global router.
 110
 111 .. code-block:: python
 112
 113    blockIssuer.state.cfg.katana.searchHalo = 10000
 114