Mike Frysinger wrote:

[...] but now we want to support dmix/dsnoop. the overhead for dmix vs non-dmix is such that we make it optional. if the user does not need software mixing, they can disable this overhead. this leads to two (incompatible) alsa config files (in this case, for the AD1980 codec). we're wondering if it's possible to have the right settings selected on the fly some how during runtime rather than having to select one file or the other.

Let's assume we have the following definitions:

AD1980.pcm.default_dmix_yes { ... } AD1980.pcm.default_dmix_no { ... }

Then we can select one of them based on a setting in some configuration file:

AD1980.pcm.default { @args [ CARD ] @args.CARD { type string } @func refer name { @func concat strings [ "cards.AD1980.pcm.default_dmix_" { @func refer name defaults.use_AD1980_dmix default yes } ":CARD=" $CARD ] } }

To disable dmix, put the line defaults.use_AD1980_dmix no into /etc/asound.conf or the user's ~/.asoundrc.

It is also possible to use the value of an environment variable:

AD1980.pcm.default { @args [ CARD ] @args.CARD { type string } @func refer name { @func concat strings [ "cards.AD1980.pcm.default_dmix_" { @func getenv vars [ USE_AD1980_DMIX ] default yes } ":CARD=" $CARD ] } }

This environment variable must be set to "no" before starting the respective application.

It is also possible to use the value of an environment variable but to fall back to some configuration setting if the env var does not exist:

AD1980.pcm.default { @args [ CARD ] @args.CARD { type string } @func refer name { @func concat strings [ "cards.AD1980.pcm.default_dmix_" { @func getenv vars [ USE_AD1980_DMIX ] default { @func refer name defaults.use_AD1980_dmix default yes } } ":CARD=" $CARD ] } }

HTH Clemens