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AR# 14290

4.1i XST - "WARNING:Xst:905 - <file>, line xx: The signals <sig1, ...> are missing in the sensitivity list of the always block."

Description

Keywords: XST, 905, signals, sensitivity, always, missing

Urgency: Standard

General Description:
During the analysis phase of XST synthesis, the following warning occurs:

"WARNING:Xst:905 - <file>, line xx: The signals <sig1, ...> are missing in the sensitivity list of the always block."

Solution

This warning will occur if an input signal of a procedural block is not listed in the sensitivity list of that block. For example:

<code>
always @(SEL or A or B or D) // Signal "C" is not listed here
begin
case (SEL)
2'b00 : MUX_OUT = A;
2'b01 : MUX_OUT = B;
2'b10 : MUX_OUT = C;
2'b11 : MUX_OUT = D;
default : MUX_OUT = 0;
endcase
end
</code>

Signal "C" is not listed in the sensitivity list -- the synthesis results will not be affected by this omission, but simulation results may differ, which prompts the warning here.
AR# 14290
Date Created 03/22/2002
Last Updated 10/07/2003
Status Archive
Type General Article