Which GPIO pins are used by SamplerBox and which ones are free?

Ted posted Dec 16 '17, 20:32:

I am messing around with a RPi 2 to use as a kind of black box to act as a piano sampler module so my sister can use my keyboard without having to learn how to use DAW's, also she says its a hassle to have to plug in her laptop every time she wants to play. (Piano player only, doesn't use any other instrument ever).

I tried using a USB DAC as suggested, but every time I test it out, I swear I can hear dropped notes and samples cutting out for the tiniest fractions of a second now and then.

The MIDI controller is USB MIDI, and my theory is that since RPi only has one US(B) bus, the sound card and controller are competing for access in certain very specific conditions that degrades performance in a noticeable way, so I am going to try using a PCM5122 DAC using the I2S bus via the GPIO pins (GPIO 18 - 21, except 20 which is input), but I'm not sure which pins are free and which ones are not in the standard image. In fact, should I even be assuming the standard dev are on the usual pins, or are they reassigned in samplerbox?

Oh also GPIO 17 is used for the IR receiver on the HAT I have, though I can't think of any uses for that.

So TLDR; I'd be very much obliged if anyone can point me to a reference doc or part of the source that lists the pin assignments, or if there is a way to find out in the shell.

Thanks in advance,

Ted posted Dec 20 '17, 21:59:

I found the answer, apparently this is pretty basic RPi info, I'm just not familiar with the platform yet.

If I understood correctly, any reasonably modern linux distribution based on Raspbian makes use of device trees for representing the hardware IO available on the RPi, and all IO is disabled by default, and has to be enabled by means of parameters or precompiled overlays in the config file in the boot sector.

I just used the iqaudio dac plus overlay and disabled onboard sound in my case with the X920 HAT.

Rien Heuver posted Dec 22 '17, 10:33:

Generic comment on raspi gpio pints: this site has it covered pretty nicely: pinout.xyz

BurchSung posted Jun 19 '18, 19:09:

Hi...i think you should now have your prompt back, but if the programs print stuff then you will see everything they are printing.
Typing "jobs" give you a list of the programs running in the background of that shell process.Also if the commands needs some time to start up consider adding a "sleep X" command between them (to sleep X seconds) so that the following command doesnt fail because it cant connect to a program still loading.


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