我在ISE的translate阶段出现了WARNING:NgdBuild:452警告，信息如下

    WARNING:NgdBuild:452 - logical net 'N45' has no driver
WARNING:NgdBuild:452 - logical net 'N46' has no driver
WARNING:NgdBuild:452 - logical net 'N47' has no driver
WARNING:NgdBuild:452 - logical net 'N48' has no driver
WARNING:NgdBuild:452 - logical net 'N49' has no driver
WARNING:NgdBuild:452 - logical net 'N50' has no driver
WARNING:NgdBuild:452 - logical net 'N51' has no driver
WARNING:NgdBuild:452 - logical net 'N52' has no driver
WARNING:NgdBuild:452 - logical net 'N53' has no driver
WARNING:NgdBuild:452 - logical net 'N54' has no driver
WARNING:NgdBuild:452 - logical net 'N55' has no driver
WARNING:NgdBuild:452 - logical net 'N56' has no driver
WARNING:NgdBuild:452 - logical net 'N57' has no driver
WARNING:NgdBuild:452 - logical net 'N58' has no driver
WARNING:NgdBuild:452 - logical net 'N59' has no driver
WARNING:NgdBuild:452 - logical net 'N60' has no driver
WARNING:NgdBuild:452 - logical net 'N61' has no driver
WARNING:NgdBuild:452 - logical net 'N62' has no driver
WARNING:NgdBuild:452 - logical net 'N63' has no driver
WARNING:NgdBuild:452 - logical net 'N64' has no driver
WARNING:NgdBuild:452 - logical net 'N65' has no driver
WARNING:NgdBuild:452 - logical net 'N66' has no driver
WARNING:NgdBuild:452 - logical net 'N67' has no driver
WARNING:NgdBuild:452 - logical net 'N68' has no driver
WARNING:NgdBuild:452 - logical net 'N69' has no driver
WARNING:NgdBuild:452 - logical net 'N70' has no driver
WARNING:NgdBuild:452 - logical net 'N71' has no driver
WARNING:NgdBuild:452 - logical net 'N72' has no driver
WARNING:NgdBuild:452 - logical net 'N73' has no driver
WARNING:NgdBuild:452 - logical net 'N74' has no driver
WARNING:NgdBuild:452 - logical net 'N75' has no driver
WARNING:NgdBuild:452 - logical net 'N76' has no driver
WARNING:NgdBuild:452 - logical net 'N77' has no driver
WARNING:NgdBuild:452 - logical net 'N78' has no driver
WARNING:NgdBuild:452 - logical net 'N79' has no driver
WARNING:NgdBuild:452 - logical net 'N80' has no driver
WARNING:NgdBuild:452 - logical net 'N81' has no driver
WARNING:NgdBuild:452 - logical net 'N82' has no driver
WARNING:NgdBuild:452 - logical net 'N83' has no driver
WARNING:NgdBuild:452 - logical net 'N84' has no driver
WARNING:NgdBuild:452 - logical net 'N85' has no driver
WARNING:NgdBuild:452 - logical net 'N86' has no driver
WARNING:NgdBuild:452 - logical net 'N87' has no driver
WARNING:NgdBuild:452 - logical net 'N88' has no driver
WARNING:NgdBuild:452 - logical net 'da902_wave/BU2/rsta' has no driver

  我找不到前面的如logical net 'N88' has no driver的警告的信号, 在我的综合信息里面也找不到如NXX这样的net，我的程序里面例化了2个DCM和一个DualPortRam，前面的几个警告应该是DCM的警告，最后一个应该是DualPortRam的警告。我的例化如下：

  DCMCLK allot_clock_1(
.CLKIN_IN(gclk), 
.CLK0_OUT(gclk_bfug),//18M
.CLK180_OUT(tlv5618_clk),//18M
.CLKFX_OUT(da_clk),
.CLKIN_IBUFG_OUT(), 
.LOCKED_OUT(dcm_lock1)
);

PLLCLK allot_clock_2(.CLKIN_IN(gclk_bfug),
.CLK0_OUT(cpld_sclk),
.CLKFX_OUT(ad9552_sclk),
.LOCKED_OUT(dcm_lock2)
);

DualPortRam da902_wave(
.clka(usb_clk),
.ena(dualram_ena), 
.wea(dualram_wea), 
.addra(dualram_wradd), 
.dina(dualram_wrdata), 
.clkb(gclk_bfug), 
.rstb(~sys_rst), 
.enb(dualram_rea), 
.addrb(dualram_rdadd), 
.doutb(dac902_data)
);
  请问找不到警告上面对应的net，这些警告怎么解决？我使用的是ISE12.4是spartan 3系列