[Jack-Devel] Why frame sizes are limited to the powers of 2?

[Filipe Coelho]

On 26.07.2017 09:39, Yuri wrote:
> On 07/26/2017 00:35, Filipe Coelho wrote:
>>
>> So some of those buffer sizes work, some do not.
>> GUIs usually show only power of 2 values because they're safer to use 
>> (I mean, more likely to actually work).
>> Also some jack applications sadly were made with the expectation that 
>> power-of-2 buffer sizes will be used...
>> But for such cases the application can return an error on start and 
>> during the jack-buffersize-callback, to force jack to be under 
>> power-of-2 sizes.
>>
>> Anyway, at least in latest jack2 this is not a problem.
>> Not sure about jack1, but I believe the same is true. 
>
>
> I use Jack1. power of 2 check is hardcoded in the server.
>
> >        if (!jack_power_of_two (nframes)) {
> >                jack_error ("buffer size %" PRIu32 " not a power of 2",
> >                            nframes);
> >                return EINVAL;
> >        }
>
> Yuri
>

This seems like a leftover that nobody cared too much about just yet.
Quickly going through the driver code I see that portaudio and coreaudio 
drivers have this restriction when starting up jackd, but alsa has that 
part disabled.
See 
https://github.com/jackaudio/jack1/blob/cb654ada4ecfd6a95b9fb648ebd33c5af462d380/drivers/alsa/alsa_driver.c#L495

The OSS code does not seem to have this restriction when starting jackd 
either.

So I think we can remove this for at least ALSA and OSS drivers, 
allowing them to change buffer size.