About spreading spare cells / flops through design

Hi All,

The following is command in ICC

spread_spare_cells

I know that it is used to spread spare cells throughout the design.
Questions are,

1. But how to know which cells one should spread ?
2. Should one create different spare cell groups which are connected to different clocks ?
3. How to decide area for spreading cells (command has switch named -bbox where you can define rectangular boundary), is it done via observation or using tool?

Regards,
Sumit

Hi,

From my knowledge spare cells are spread so that it could be used if any other cells fails post fabrication. Generally Nand gates will be spread as spare cells and few spares cells will be spread for each module depending on user specification.

Correct me if i am wrong.

hai sumit,

1>
normally in our company we will pick a cell [medium dirve strength ] random form all logic ..eX:- and,or,nor,mux,nand etc..,
2>
up to my knowledge spare cells are not connected respect to clock.. So far we havent done separate group spare cells for clock.. if so please explain..

3> I have experience on soc encounter.. In that we will set box with assumption not accurate.. we will place less spare cells if we are have small areas.. based on that we set xstepx and xstepy value..

i herewith attached a sample for u

set spareModuleName "SPARE_CELLS"
set xStep 75
set yStep 75

#Creating Spare module
createSpareModule -moduleName $spareModuleName -cell { ADDFHX8M AND3X1M AO21XLM AO22X1M AO2B2BX1M AOI2BB1X8M BUFX12M CLKINVX1M CLKNAND2X16M CLKXOR2X2M INVXLM NAND4BBXLM NOR2X5M OR3X2M XNOR3X2M MX2X2M } -tie $tie_cells


placeSpareModule -moduleName $spareModuleName -util 0.3 -stepx $xStep -stepy $yStep -offsetx 20 -offsety 20