CLK_OF_DECLARE advice required

Stephen Warren swarren at
Wed May 31 08:27:07 PDT 2017

On 05/30/2017 06:23 AM, Phil Elwell wrote:
> Hi,
> I've run into a problem using the fixed-factor clock on Raspberry Pi and I'd
> like some advice before I submit a patch.
> Some context: the aim is to use a standard UART and some external circuitry
> as a MIDI interface. This would be straightforward except that Linux doesn't
> recognise the required 31.25KHz as a valid UART baud rate. Rhe workaround is
> to declare the UART clock such that the reported rate differs from the actual
> rate. If one sets the reported rate to be (actual*38400)/31250 then
> requesting a 38400 baud rate will result in an actual 31250 baud signal.

This sounds like the wrong approach. Forcing the port to use a different 
clock rate than the user requests would prevent anyone from using that 
port for its standard purpose; it'd turn what should be a runtime 
decision into a compile-time decision.

Are you sure there's no way to simply select the correct baud rate on 
the port? I see plenty of references to configuring custom baud rates 
under Linux when I search Google, e.g.:

"How to set a custom baud rate on Linux?"

"Re: Terminal interface and non-standard baudrates"

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