Syncing to vertical blank, VBLANK, with ati fglrx linux driver.

Argh... this took me all morning to figure out. I will put this up my website, and point google to it, so that others may suffer less than I did.

Nowhere on the web, could I find how to have ati's linux driver, called fglrx, synchronize with the display. To have glxgears run at display frequencies, in my case 60 Hz, I had to edit /etc/X11/XF86Config-4 to contain this line in the device section:

        Option "Capabilities" "0x00000800"

It turned out that bit 11 in this capabilities bitfield enables vblanking. I had to diff multiple runs with fglrxconfig to find this out, so that you don't have to :-)