Use the recommended tool wizards provided by the manufacturer of your part.ģ. Read the recommendation in the clocking documenation for your part family.Ģ. Stick to the recommendation above and you will avoid numerous problems. You can go research the problems associated with gating a clock if you want to explore more. Others might recommend using some logic to divide a clock, but in my personal opinion, this is not recommended for many reasons that is beyond the scope of my answer. This is the recommended way of doing a clock divider so that your routing and timing performance doesn't run into any issues. After using the GUI, it will generate some output files that you can use like a core in your design where it's handling all of the complex stuff for you. The wizard also lets you turn on some advanced features if desired and will tell you specs like jitter performance. The wizard will then set the multiplier and dividers for the channels to try to achieve the output frequency that you want and even tell you what the actual frequency will be. You can then set what output frequency you want on each of the available output channels. Xilinx tools will let you go use the clock wizard in their GUI where you can set up exactly what you want by putting in the input clock frequency, whether it's coming from a single ended pin, differential pins, or global buffer. The figure shows the example of a clock divider. In other words the time period of the outout clock will be twice the time perioud of the clock input. So for example if the frequency of the clock input is 50 MHz, the frequency of the output will be 25 MHz. If you have plenty of resources available and only a few clock needs, use the MMCM. A clock Divider has a clock as an input and it divides the clock input by two. An MMCM is a superset of PLL, so depending on which part you have and the needs of your design will determine which one to use. What Xilinx commonly recommends is that you handle clock dividers with their dedicated primitives which includes PLL's and MMCM's. Here's an example for the Xilinx Ultrascale:
CLOCK DIVIDER VHDL HOW TO
As an example, Xilinx provides detailed recommendations on how to handle clocking for each of their FPGA part families.
With that said, for clocking, you need to consult the documentation for the part family that you are designing for. Many designs need multiple different clock frequencies. Typically, board oscillators will provide a specific frequency into a part pin that may or may not be the frequency that you need for your design. Needs testing anyway.VHDL Clock Divider PurposeThe purpose of a clock divider is to get the clock frequency that you need for the design. A clock (or frequency) divider is a particular type of two-window signal generator, which takes the clock as input and produces at the output a signal whose. You need to look at the initial conditions.
Ap_clk2 : assert property ( ( posedge clk ) # 1 |-> clk2 =!$past (clk2 ) ) Īp_clk4 : assert property ( ( posedge clk ) # 2 clk2 = 0 |->Ĭlk4 =!$past (clk4, 2 ) ) // The antecedent #1 and #2 are just used for initialization, since the clk2 and clk4 have not started.
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