XFree86 provides a facility for setting the clock frequency on a graphics card by an external program. This is provided to make it possible to deal with cards that use clock selection methods not supported by the standard drivers.
This facility is enabled by adding a ClockProg line to the
Device section of the XF86Config file.
The format of this line is:
ClockProg "commandpath"
When using this option, a Clocks line is required in the Device section of
the XF86Config file to tell the server which clock frequencies are
available to it. In the case of a card that has a fixed set of preset
clocks, the ordering of the clocks in the Clocks line should
correspond to what the card/program expects.
In the case of a card which has a fully
programmable clock (like the SS24) the ordering is not important, and the
values chosen can be anything in the range supported by the card. Up to
32 clock values may be specified.
The server calls the external program when it needs to change the clock frequency. This occurs at startup and when switching modes with the hot-key sequences. The command is passed two command-line arguments. The first is the clock frequency in MHz (as a floating point number -- currently specified to the nearest 0.1 MHz). The second argument is the index of the clock value in the Clocks list (the first clock is index 0). Cards with a fixed set of clocks would probably make use of the index, while cards with a fully programmable clock would use the frequency argument.
Next Chapter, Previous Chapter
Table of contents of this chapter, General table of contents
Top of the document, Beginning of this Chapter