Implementation

[adamhebert]

I am using the ML605 dev board for testing and I am having a bit of a problem. I have a fibre channel instance and want to route one of the clocks out of it to the user sma clock on the board. I get the following warning:

WARNING:Route:436 - The router has detected an unroutable situation for one or more connections. The router will finish the rest of the
design and leave them as unrouted. The cause of this behavior is either an issue with the placement or unroutable placement constraints.
To allow you to use FPGA editor to isolate the problems, the following is a list of (up to 10) such unroutable connections:
Unroutable signal: sma_clk_OBUF pin: sma_clk/O

After this I do not get any errors but Place and Route fails. I am pretty sure it is because of this unroutable signal. I think sma_clk_OBUF is the signal coming from the output buffer but I do not understand why its not being routed to the pin. Any idea how what is happening or how it can be fixed.

[austin · Accepted solution]

a,

Global clcok pins a dedicated to inputs, only.

If you wish to "see" a clock externally, route it to a general purpsoe IO (best is to use two pins as LVDS), and clock the IOB DDR DFF (known as "clock forwarding") to get a perfect represenation of the internal clock, externally.

[adamhebert]

Thank you. I did not know about this.