title: new to Zedboard : how to allocate "clk" pin number on the zedboard?
body: <p>I'm very new to Zedboard. I'm writing a counter in VHDL, and try to implement it on the Zedboard Zynq 7000 XC7Z020-1 CSG484CES EPP.</p>
  
  <p>When I allocate the pin, I want to have a clock. But it seems wrong to allocate "clk" to a user switch. So I looked up the document <code>ZedBoard_HW_UG_v1_1.pdf</code>. </p>
  
  <p>In chapter 2.5, it says the following:</p>
  
  <blockquote>
    <p>The EPP’s PS subsystem uses a dedicated 33.3333 MHz clock source, IC18, Fox 767-
    33.333333-12, with series termination. The PS infrastructure can generate up to four PLL-based clocks for the PL system. An on-board 100 MHz oscillator, IC17, Fox 767-100-136, supplies the PL subsystem clock input on bank 13, pin Y9.</p>
  </blockquote>
  
  <p>But when I allocate <em>NET "clk" LOC = Y9;</em>, it seems doesn't work! I can't find where the clk is! There suppose to be a button or something that I can control, right?</p>
  
  <p>The warning is this:</p>
  
  <p>PhysDesignRules:2452 - The IOB q&lt;1> is either not constrained (LOC) to a specific location and/or has an undefined I/O Standard (IOSTANDARD). This condition may seriously affect the device and will be an error in bitstream creation. It should be corrected by properly specifying the pin location and I/O Standard.</p>
  
  <p>every pin has a warning like this. 
  And here is my ucf file:</p>
  
  <pre><code>NET "clk" CLOCK_DEDICATED_ROUTE = FALSE;
  NET "q[6]" LOC = T22;
  NET "q[5]" LOC = T21;
  NET "q[4]" LOC = U22;
  NET "q[3]" LOC = U21;
  NET "q[2]" LOC = V22;
  NET "q[1]" LOC = W22;
  NET "q[0]" LOC = U19;
  
  NET "d[6]" LOC = G22;
  NET "d[5]" LOC = H22;
  NET "d[4]" LOC = F21;
  NET "d[3]" LOC = H19;
  NET "d[2]" LOC = H18;
  NET "d[1]" LOC = H17;
  NET "d[0]" LOC = M15;
  NET "clk" LOC = Y9;
  NET "clr" LOC = T18;
  NET "alm" LOC = U14;
  </code></pre>
  
  <p>Where can I find a document explain what I need to do?
  And if Y9 is the correct choice for clock, how can I know the upper edge has come? since there's no botton that I can operate?
  A lot of thanks!!!</p>