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Diffstat (limited to 'docs/devel/clocks.rst')
| -rw-r--r-- | docs/devel/clocks.rst | 23 |
1 files changed, 23 insertions, 0 deletions
diff --git a/docs/devel/clocks.rst b/docs/devel/clocks.rst index 956bd147ea..675fbeb6ab 100644 --- a/docs/devel/clocks.rst +++ b/docs/devel/clocks.rst @@ -260,6 +260,29 @@ clocks get the new clock period value: *Clock 2*, *Clock 3* and *Clock 4*. It is not possible to disconnect a clock or to change the clock connection after it is connected. +Clock multiplier and divider settings +------------------------------------- + +By default, when clocks are connected together, the child +clocks run with the same period as their source (parent) clock. +The Clock API supports a built-in period multiplier/divider +mechanism so you can configure a clock to make its children +run at a different period from its own. If you call the +``clock_set_mul_div()`` function you can specify the clock's +multiplier and divider values. The children of that clock +will all run with a period of ``parent_period * multiplier / divider``. +For instance, if the clock has a frequency of 8MHz and you set its +multiplier to 2 and its divider to 3, the child clocks will run +at 12MHz. + +You can change the multiplier and divider of a clock at runtime, +so you can use this to model clock controller devices which +have guest-programmable frequency multipliers or dividers. + +Note that ``clock_set_mul_div()`` does not automatically call +``clock_propagate()``. If you make a runtime change to the +multiplier or divider you must call clock_propagate() yourself. + Unconnected input clocks ------------------------ |