check_timing command (registers with no clock defined)

Hi guys

In quartus sdc "check_timing" documentation it says:

"The no_clock check reports whether registers have at least one clock at their clock pin, and that ports determined to be clocks have a clock assigned to them, and also checks that PLLs have a clock assignment."

This is really confuses me.

First of all, if registers don't have a clock, they will be automatically removed in synthesis phase.

consider this case:

module regs_noclock (

input clk,

input data_in,

output data_out

);

reg q0,q1;

wire genclk

assign genclk = q0;

assign data_out = q1;

always @(posedge clk)

q0 =~q0;

always @(posedge genclk)

q1 = data_in;

endmodule

I didn't generate any sdc for this example. the genclk is undefined( or that's what i understood)

still when I run the command "check_timing -include {no_clock}" it return 0. so the genclk is know for the tool as a clock.

the question is : in which case timequest reports registers with no clock defined?

Maybe this will give a clear idea: in xilinx, they have the following message: "there are 42 reg/latch with no clock driven by root clock pin"

thanks