XEM7310 Clock Speed in XDC

VHDL / Verilog Discussion
1

Trying to resolve something about the clock I don’t fully understand. Specifically line 70 in the XEM7310 counters xdc file. The period is for a 100.8MHz clock and the system clock is 200MHz. Does this mean that the okHost is running on a 100MHz clock and I need to cross the time domain from things on the sys_clk? I haven’t done that before (XEM6310) and trying convince myself I don’t care about this now.

The line for reference:
ln70: create_clock -name okUH0 -period 9.920 [get_ports {okUH[0]}]
ln96: create_clock -name sys_clk -period 5 [get_ports sys_clkp]

Thanks,
Sam

2

Hi Samuel,

To clarify, the okHost clock (okClk) runs at 100.8 MHz, and the fabric clock runs at 200 MHz. Depending on your design, you may need to perform CDC for signals crossing into a different clock domain. Vivado timing analysis and behavioral simulation can assist you with analyzing signals crossing into another clock domain.

3

Please note that our camera reference design is located here:

The HDL for this design incorporates at least a few strategies for CDC:

  1. okTriggerIn and okTriggerOut components are built into the FrontPanel SDK. These perform reliable single-bit crossings.
  2. sync_bus.v is useful for crossing a collection of signals for low-performance.
  3. sync_reset.v is a handy way to provide a reliable reset signal to state machines in another domain.
  4. For bulk traffic such as image buffers, the asynchronous FIFO is fast and reliable. Xilinx provides IP cores for this.
4

Well, looks like this is a case of a blind squirrel finding a nut. Because of how I setup things to be hand shaking, it masked the error in speeds. This is probably why I have had issues with Triggers and Pipes as I had them on the fabric clock and not on the host clock. It seems obvious now but the more you know…

The Camera reference design is gold as it combines a lot of the simpler project elements. Didn’t know about that and was looking at the ones packaged in the FrontPanel distribution. This also preempted my question on BT Pipes.

Thanks for the quick responses!
Sam