Quartus : Master clock could not be derived
I am working on Stratix 10 and Quartus 18.1 pro.
Im using a PLL created with the IP 'IOPLL' in order to create a 40MHz clock from a 320MHz clock input from Si5341 ("pll_40").
Normally, I don't have to define both clocks since they are respectively 'iopll_refclk' and 'iopll_outclk' and so are defined in the ip.
I have another pll, almost the same, which is creating its own clocks constraints without problem ("pll_gen").
So where is the difference and why do I have these error messages :
Warning(332087): The master clock for this clock assignment could not be derived. Clock: ip|iopll_0_n_cnt_clk was not created.
Warning(332035): No clocks found on or feeding the specified source node: ip|iopll_0|stratix10_altera_iopll_i|s10_iopll.fourteennm_pll|refclk[0]
Thanks in advance,