[oss-devel] wrong documentation for MIXT_SLIDER in oss4 mixer api?

[Clive Wright]

apriori at dkc-clan.de wrote:
> Hi all,
> 
> I'm currently hacking around in kmix to add at least basic OSS4 support. I've 
> got an usb device with a output.vol control with a value range of 0 - 37. I 
> of course get values much higher than that when reading from the mixer 
> device. The normal procedure as shown in the doc and in the ossmix source is 
> to clamp (is that the right word?) with a bitmask. 
> 
> According to the documentation the value is a 31 bit positive integer, 
> therefore the bitmask should be 0xFFFFFFFE - but that would be wrong, because 
> I'd get values of about 9k, whereas I need 0 - 37, which I get when using the 
> bitmask 0xFF and AND the value with it. 
> What's wrong here, me or the documentation?
> 

If control is graduated in centibels required range is probably 0 to 370
whereas kmix is probably 0 to 100 so you will have to apply a scaling 
factor (kmix * 37 / 10 = ossmix). Ideally mixer should read max. value 
and scale accordingly.

Bit masking should be used depending on the type of control to separate 
the channels.
MIXT_STEREOSLIDER is 8 bits per channel whereas MIXT_STEREOSLIDER16 is 
16 bits per channel ie maxvalue is 0x01720172 so masking with 0x0000FFFF 
would select just the left channel. Shift and mask for the other channel.

regards,
Clive