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AR# 6733

Vitex BRAM VHDL simulation: setup violation on CLK A with respect to CLK B, or setup violation on CLKB with respect to CLK A

Description

Keywords: setup, error, violation, BRAM, dual port, simulation

Urgnecy: Standard

General Description:

I am doing a VHDL simulation and I am getting a setup violation on
CLKA with respect to CLK B, or setup violation on CLKB with
respect to CLKA. It does this for every clock edge.

I am using a Virtex Block ram in my design, and I am using the same
clock for PORT A and PORT B. I have the Port A and Port B
adress' at different locations.

How can I be getting setup violation on the clocks when I am using
the same clock for both ports?

Solution

The problem you are experiencing is an error in the VHDL simulation model
for the RAMB4. The following is the change that will fix the problem. This
fix is implemented in the Xilinx 2.1i release. After making the following
changes the library will have to be re-compiled.

In every model for [X_]RAMB4_S*_S* in simprim and unisim libraries in
Port B code, the following lines should change:

line 11832(In my copy) in 1.5 was
if (VALID_ADDRB AND Tviol_CLKB_CLKA_posedge /= 'X') then
DOB_zd := MEM((ADDRESS_B*DIBW + DIBW_1)
downto (ADDRESS_B*DIBW));
else
DOB_zd := (others => 'X');
end if;

should change to:

if (VALID_ADDRB ) then
if ( WEA_ipd = '0' OR Tviol_CLKB_CLKA_posedge /= 'X'
OR (HAS_OVERLAP = FALSE)) then
DOB_zd := MEM((ADDRESS_B*DIBW + DIBW_1)
downto (ADDRESS_B*DIBW));
end if;
else
DOB_zd := (others => 'X');
end if;

The vhd file will need to be re-compiled for the changes to take
effect.

This is fixed in 2.1i
AR# 6733
Date Created 08/31/2007
Last Updated 09/30/2008
Status Archive
Type General Article