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AR# 35155

11.5 - PlanAhead IOB DRC check confusing when Prohibits and MGTs are included in the design

Description


Using a design which includes both Prohibits and MGTs can lead to confusing DRC errors in PlanAhead.
For example, relates to a xc6vlx240tff1759 part where errors from PlanAhead DRC checks for a design containing 45 Prohibits and 86 MGT pins:
"IOCNT #1 Fatal Design has more IOs (683) than placeable pins on the package (675)"

MAP reports the following:
"Number of bonded IOBs: 597 out of 720 82%"

The reports show conflicting information which is confusing.

Solution


PlanAhead DRC for IOBs takes into account Prohibits when calculating available I/Os on the device. As a result, there might be a difference between the available I/Os reported in PlanAhead and the available I/Os reported in MAP and PAR.
In the example, there are 45 Prohibits in the design (i.e., 720 pins - 45 Prohibits = 675 Pins available; the amount reported by PlanAhead). This is expected behavior in the PlanAhead software and was added in 11.1.
Another confusing part of the above DRC error shows PlanAhead reporting 683 I/Os in the design, but MAP reports 597. The MAP number is indeed correct while the DRC in PlanAhead takes into account MGT pins and treats them as I/O. In the example, there are 86 MGT pins (597 + 86 = 683). This is a known issue in 11.5 and is scheduled to be fixed in 12.1.
AR# 35155
Date Created 06/21/2010
Last Updated 05/23/2014
Status Archive
Type General Article
Devices
  • Spartan-6 LX
  • Spartan-6 LXT
  • Virtex-6 SXT
  • More
  • Virtex-6 LX
  • Virtex-6 HXT
  • Virtex-6 CXT
  • Virtex-6 LXT
  • Less
Tools
  • PlanAhead - 11.1
  • PlanAhead - 11.2