Need to run ALTGXB XAUI mode at half the rate...

Hi,

I'm using a ATL2GXB function in an ArriaGX which is running in XAUI mode (3.125gbps). The input clock is 156.25MHz. What I want to do is run it half the rate i.e. 1.5625gbps.

In the documentation there is a div2 on the REFCLK input which would be perfect if I could access it. I've tried changing it in the parameter file that is created when the ALT2GXB is generated but the tools don't allow it. It would be perfect as I could keep the code as is and run it at the reduced rate.

The only other way I can think of is to run it in Basic mode which gives full control over the settings. Differences between Basic and Xaui modes:

1. The rate pattern matchers were different in value:

(a) Basic mode had 20-bits and the pattern1 was 0xD0E83 and pattern2 was 0x2F17C.

(b) With Xaui it was 10 bits with the pattern1 0x343 and pattern2 0x0BC.

2. Xaui mode had a deskew fifo but Basic mode didn't.

I don't know if it's possible to do this by switching off the pattern matchers in Basic mode. Both modes use the same word alignment pattern but I don't know if that's enough.

Your help would be most appreciated.

Regards

MT