[alsa-devel] [PATCHv4 2/2] ASoC: OMAP-McBSP: ASoC interface for McBSP sidetone

ilkka.koskinen at nokia.com ilkka.koskinen at nokia.com
Mon Feb 22 12:11:32 CET 2010


>From: Nurkkala Eero.An (EXT-Offcode/Oulu) 
>Sent: 19 February, 2010 21:04
>> Oops, I seemed to copy Q1.14 instead of Q14.1, but isn't it 
>still the same.
>> When I added some debug messages it still seemed to be corret.
>> Lowest number (-32768) is represented with 16th bit '1' and 
>the rest are
>> zeros, right? That is 0x8000.
>> -1 has all the bits set (0xffff) and 0 has all the bit 
>cleared (0x0000).
>> Highest positive value has 16th bit cleared and the rest set 
>> Or did I interpret something wrong?
>> Cheers, Ilkka
>I guess it's just fine, but let's see. Maybe I was lost in the 
>Q1.14: m + n + 1 ~
>binary: [sign bit, (m), (n)] where m is the integer portion, 0 
>or 1, n is 14 bits..
>so  if your input was [-32768... 32767] -> [-2,2] then, for example,
>-32768 is in hex: 0x8000, but the 2nd most significant bit is 
>zero, which means
>the integer portion (m) is not 1, which makes me doubt the 
>gain -32768 is
>actually -1 (or 0), not -2. But then, as it's a two's 
>complement, it maybe just correct.
>So most likely it's just fine; I just had a thinko.

Ok, now I got your point :) However, as far as I can understand
the Q notation right, it basically defines how to interpret the 
value. That is, where is the decimal point. Thus, I would say that
the code should work fine and based on quick tests, the gain control
seems to behave ok too.

Cheers, Ilkka

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