Challenge 5 : calculate total stcell count
Hi All,
below case will test your practical concepts related to Floorplan.
suppose, there is one design without any macros/IPs with Floorplan Aspect ratio as 1. site row height as 0.169 and site row width is 0.048. in all stdcells, applied keepout : left --> 0.24 , right --> 0.24 . left/right side core to die offset as 0.624 and top/bottom core to die offset is 1.014.
for this design placeopt is completed (stdcells are legalized properly).
After completing placeopt, all Physical/Special cells are removed manually and also stdcell apart from instances with cell reference as INV8 are removed. (i.e. design is having only INV8 ref cells).
stdcell utilization : 0.6 , Total stdcell area : 476.3772 , Total Core area : 793.962
From LEF, area of INV8 : 0.15412800
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What will be Total stdcell count ..?
comment your answer below.
To revise Floorplan concept related to blockages/keepout, Please check below post:
The total std cell area = INV8 instance area + other std cells area. Without knowing the detail like how many number of INV8 instances are design, how will we calculate the other std cells count.
ReplyDeletePlease let me know if I've understood it wrong.
Hi Shubham,
DeleteAll are INV8 instances only. Other stdcells are deleted..
Can we assume area of std cell and area of INV8 equal
DeleteDesign is having only 1 stdcell ref, that is INV8 only.
DeleteAll instances are of INV8 ref only
Area of Inv8 cell = LEF Area of INV8 + left keepout margin area + right keepout margin area
ReplyDelete= 0.15412800 + 2 x (0.24*0.169)
= 0.235248
Total Std.cell count = Total Std. Cell Area / Area of Inv8 cell (including keepout margin)
= 476.3772/0.235248
= 2025
Let me know if I am right or wrong?
Hi Aman,
DeleteAs this is 2025 year, 2025 is 💯 correct answer...!!😃
You are absolutely right 👍 here..
Main point to understand here is when tool calculates the Utilisation, always keepout values is already considered..
Thank you Jignesh 😀
DeleteAnd thank you so much for posting such a great content.
Aman, how did you calculated keepout area ?
DeleteINV cell area in LEF = 0.154128 um2
ReplyDeleteHieght of INV cell = Site row height = 0.169 um (Height of std cell is same as site row height)
To find width of INV cell -->
Area of one site = Site row height * site row width = 0.169*0.048 = 0.008112 um2
So,
No. of site = Area of INV in lef / Area of one site = 0.154128 / 0.008112 = 19
So, width of INV cell = 19 * Site row width = 19 * 0.048 = 0.912 um
Now,
Need to find area of inv cell considering keepout margin
Keep out margin = 0.24 on both left and right.
So, Width of cell = 0.912 + 0.24 + 0.24 = 1.392
Area of INV cell with Keepout = 0.169 * 1.392 = 0.235248
Number of std cells = Total area of std cells / Area of one cell = 476.3772 / 0.235248 = 2025
Ans - 2025 std cells.
Hi Afroz,
DeleteYes. 2025 is correct answer (as current year is 2025!)
Was my method of solving right?
DeleteAfroz,
DeleteYour calculation is right only but would suggest to think how this can be achieved in shorter way..
Check Aman's calculation in comment.
Okay Sir
Delete