On 03/13/2017 01:39 PM, Felix Bruns wrote:

Hi,

I am working on embedded device (using an i.MX6 MCU) which has an external amplifier.

Unfortunately I could not find much information if and how the gain of hardware amplifiers are controlled by alsa. (The only example for hardware amplification I found is the arcam-av plugin...)

Is creating a plugin the recommended way of supporting (external) hardware amplification in alsa? Can somebody clarify or point me to another example?

Usually the amplifier is integrated in the overall sound card that is presented to userspace. No special plugins needed. The recommended way for implementing this is to use ASoC since ASoC allows to easily assemble a sound card from multiple components.

The amplifier is implemented as a standalone driver and there is a so called machine driver that puts all the different components together.

For examples of amplifier drivers see the "Amps" section in sound/soc/codecs/Makefile. For an example of a machine driver that uses an external amplifier have a look at sound/soc/omap/rx51.c.

- Lars