Backport of audio documentation from masterflounder_6.0.3flounder/6.0.36.0.3

Documentation was available only on master. New documentation website is
now by branch, so documentation should be available on both branches.

Bug: SPEC-1993

Change-Id: I55484d5c1f28ae1e7fa927533b3dd862a03ed207
Signed-off-by: Loïc Collignon <loic.collignon@iot.bzh>

1 files changed, 46 insertions, 0 deletions

diff --git a/docs/high-level-api/TipsAndTricks/HALs.md b/docs/high-level-api/TipsAndTricks/HALs.md
new file mode 100644
index 0000000..4c2ead6
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+# HALs
+
+HALs are known as json files in 4a, they are stored in
+**/usr/libexec/agl/4a-hal**.
+
+Enabled HALs can be found in the **etc** subfolder, and disabled HALs in
+**etc.available**.
+
+You can enable and disable HALs just by moving the corresponding json file from
+one folder to the other.
+
+Example:
+
+```bash
+user@machine$ ls etc etc.available/
+etc:
+hal-4a-csl-cm106-8ch-usb.json
+
+etc.available/:
+hal-4a-2ch-generic-usb.json  hal-4a-intel.json
+hal-4a-ensoniq.json          hal-4a-jabra.json
+hal-4a-intel-minnow.json     hal-4a-rcar-m3.json
+hal-4a-intel-qemu.json       hal-4a-rcar-m3kf.json
+
+user@machine$ mv etc/hal-4a-csl-cm106-8ch-usb.json  etc.available
+user@machine$ mv etc.available/hal-4a-2ch-generic-usb.json etc
+
+user@machine$ ls etc etc.available/
+etc:
+hal-4a-2ch-generic-usb.json
+
+etc.available/:
+hal-4a-csl-cm106-8ch-usb.json  hal-4a-intel.json
+hal-4a-ensoniq.json            hal-4a-jabra.json
+hal-4a-intel-minnow.json       hal-4a-rcar-m3.json
+hal-4a-intel-qemu.json         hal-4a-rcar-m3kf.json
+
+user@machine$ sync
+user@machine$ reboot
+```
+
+>NOTE: Even if multiple HAL are allowed, you have to make sure that they don't
+>provide the same streams, because it will cause a race condition in the high
+>level API. The first HAL providing the stream is used, any other are ignored.
+>
+>Also, the hardware used by enabled HALs should be available.