Using an External Clock

[rp181]

If I have an external clock of 80 MHz, can I clock a port to this? The XC Programming guide shows how to use an external clock, but can the pins sample a 80 MHz single? From what I am understanding, the XMOS can sample edges at 100 MHz, or a cycle frequency of only 50 MHz, and 80 MHz clock cycles would exceed this.

Instead of using an external clock, is there a way to clock a port at 80 MHz? The closes I can get (on a 500 MIPS device) is 83.3333 MHz: Reference frequency of 500 MHz, divider of 6.

EDIT: I found a topic posted earlier on XMOS, and it basically said if I set the reference frequency to 500 MHz, and use a clocked port, 250 MHz should be possible. Correct me if I am wrong!

EDIT EDIT: I tried it and it seems to be working. I put the reference frequency as 500 MHz, but I get this:

Code: Select all

xmap: Warning: Node "0" does not have 100Mhz reference clock.

Should I be worried?

[Bianco]

Just ignore that warning, it has been bugging me for some while too :-)

I don't see how you get 80MHz from 250MHz though.