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."
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.