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AR# 5134

LogiCORE PCI - During Cadence Verilog-XL simulation, a warning reports: "Timing violation in bic_pci_stm.bic_pci_top..."

Description

General Description: 

Cadence Verilog-XL issues the following warning when I simulate the LogiCORE PCI interface: 

 

"/xilinx/xilinx.M1.5/verilog/src/simprims/X_FF.vmd", 71: 

Timing violation in bic_pci_stm.bic_pci_top.\PCI_CORE/PCI_LC/PCI-AD/IO9/IFD/$1I37/X_FF 

$setup( IN:298578982, posedge CLK &&& in_clk_enable:298579228, 360:360 );" 

 

What does this warning mean?

Solution

In order to meet timing, the LogiCORE PCI turns on its AD drivers during the clock cycle BEFORE it asserts FRAME#. Therefore, the value on AD may change any time between the start of the clock cycle before FRAME# and the end of the clock cycle DURING which FRAME# is asserted. If the change occurs within the setup/hold window around the intermediate clock edge, a violation will occur when the AD IOB's input FF tries to clock in the value.  

 

Because the core does not rely on this indeterminate value, this warning may be safely ignored.

AR# 5134
Date Created 08/21/2007
Last Updated 05/14/2014
Status Archive
Type General Article