4a-kickstart-Loic-IoTbzh-Dresden-2018.pdf

1. 4A (AGL Audio Advanced Architecture)
Kickstart with AGL/FF
English presentation Oct. 18
Loïc Collignon – Embedded Engineer
loic.collignon@iot.bzh

2. Oct 17, 2018 2
IoT.bzh
IoT.bzh team
●
Mostly dedicated to AGL
●
https://iot.bzh/en/
●
http://github.com/iotbzh
Workshop in Lorient
LORIENT
vannes

3. Oct 17, 2018 3
4A Kickstart
Loïc Collignon
High Level API
Jonathan Aillet
HALs
Thierry Bultel
SoftMixer

4. Oct 17, 2018 4
4A Kickstart
●
I have this OGG file, how do I play it?

5. Oct 17, 2018 5
4A Kickstart
●
I have this OGG file, how do I play it?
– Use alsa, Gstreamer, etc., 4A doesn’t play any
audio! It handles permissions, signals and policies.

6. Oct 17, 2018 6
4A Kickstart
●
Why do we need this extra layer of complexity?

7. Oct 17, 2018 7
4A Kickstart
●
Why do we need this extra layer of complexity?
– Because a car is not a home Hi-Fi system:
●
Multiple concurrent audio sources (i.e.
navigation+multimedia)
●
Features required by law (i.e. emergency notifications,
turn indicators sound, ...)
●
Ambiant noise (i.e. speed correlated noise)

8. Oct 17, 2018 8
4A Kickstart
●
Applications still have to use audio libraries
(i.e. Gstreamer)
●
Applications also have to use 4a
HARDWARE
APPLICATIONS
Audio lib 4a

9. Oct 17, 2018 9
4A Kickstart
1) Open the audio-role
you want
2) Use the returned
device to play audio
3) Close the audio-role
when finished

10. Oct 17, 2018 10
4A Kickstart
ahl-4a/get_roles
{
“response”: [
“multimedia”,
“navigation”,
“emergency”
]
}

11. Oct 17, 2018 11
4A Kickstart
ahl-4a/<role> { “action”: “open” }
{
“response”: {
“device_uri”: “hw:2,0,1”
}
}

12. Oct 17, 2018 12
4A Kickstart
json_object *jsonData = json_object_new_object();
json_object_object_add(jsonData, "action", json_object_new_string("open"));
ret = afb_service_call_sync("ahl-4a", "multimedia", jsonData, &response);
if (!ret) {
json_object *valJson = NULL;
json_object *val = NULL;
gboolean ret;
ret = json_object_object_get_ex(response, "response", &valJson);
if (ret) {
ret = json_object_object_get_ex(valJson, "device_uri", &val);
if (ret) {
char* jres_pcm = json_object_get_string(val);
g_object_set(data.alsa_sink, "device", jres_pcm, NULL);
}
ret = json_object_object_get_ex(valJson, "stream_id", &val);
if (ret) int stream_id = json_object_get_int(val);
}
}

13. Oct 17, 2018 13
4A Kickstart
ahl-4a/<role> { “action”: “volume”, “value”: 80 }
ahl-4a/<role> { “action”: “volume”, “value”: “+50” }
{
“response”: {
“volnew”: 80,
“volold”: 30
}
}

14. Oct 17, 2018 14
4A Kickstart
●
Audio roles
– Multimedia
– Navigation
– Emergency
– ...
●
Interruptions
– Ramp
– Mute
– Pause
– ...

15. Oct 17, 2018 15
4A Kickstart
"roles":[
{
"uid": "multimedia",
"description": "Multimedia content",
"priority": 0,
"stream": "multimedia"
},
{
"uid": "emergency",
"description": "Safety-relevant or critical alerts/alarms",
"priority": 100,
"stream": "emergency",
"interrupts":[
{"type": "ramp", "args": { "uid": "ramp-fast", "volume": 30} }
]
}
]
}

16. Oct 17, 2018 16
4A Kickstart
●
What is an audio role?
●
An abstraction on which we can apply permissions and
policies
●
It’s not an audio card

17. Oct 17, 2018 17
4A Kickstart
●
What is an audio stream?
●
A device that can play audio
●
Can be virtual
●
Set up at the factory

18. Oct 17, 2018 18
4A Kickstart

19. Oct 17, 2018 19
4A Kickstart
●
HALs
●
Abstract the hardware
●
Maps ALSA controls
●
Exposes streams
●
Use the controller

20. Oct 17, 2018 20
4A Kickstart
"ramps": [
{
"uid": "ramp-fast",
"delay": 50,
"up": 2,
"down": 10
},
],

21. Oct 17, 2018 21
4A Kickstart
"playbacks" : {
"uid": "RCAR-M3",
"path": "/dev/snd/by-path/platform-sound",
"params": { "rate": 48000, "format": "S24_LE" },
"sink": {
"controls": {
"volume": { "name": "DVC Out Playback Volume", "value": 80 },
"mute": { "name": "SRC Out Rate Switch" }
},
"channels": [ { "uid": "front-right", "port": 0 }, { "uid": "front-left", "port":
1 } ]
}
},

22. Oct 17, 2018 22
4A Kickstart
"captures": {
"uid": "RCAR-M3",
"path": "/dev/snd/by-path/platform-sound",
"params": {
"rate": 48000
},
"source": {
"controls": {
"volume": { "name": "DVC In Capture Volume" },
"mute": { "name": "DVC In Mute Switch" }
},
"channels": [
{ "uid": "mic-right", "port": 0 },
{ "uid": "mic-left", "port": 1 }
]
}
},

23. Oct 17, 2018 23
4A Kickstart
"zones": [
{
"uid": "full-stereo",
"sink": [
{ "target": "front-right", "channel": 0 },
{ "target": "front-left", "channel": 1 }
]
},
{
"uid": "front-seats",
"sink": [
{ "target": "front-right", "channel": 0 },
{ "target": "front-left", "channel": 1 }
]
}
],

24. Oct 17, 2018 24
4A Kickstart
"streams": [
{
"uid": "multimedia",
"verb": "multimedia",
"zone": "full-stereo",
"volume": 60,
"mute": false,
"params": { "rate": 48000, "format": "S16_LE" }
},
{
"uid": "emergency",
"verb": "emergency",
"zone": "front-seats",
"volume": 60,
"mute": false,
"params": { "rate": 48000, "format": "S16_LE" }
}
]

25. Oct 17, 2018 25
4A Kickstart
●
Softmixer
●
Uses snd-aloop to provide virtual devices
●
Maps streams to actual hardware
●
Provides basic mixing capabilities

26. Oct 17, 2018 26
4A Kickstart
Any question?

27. Oct 17, 2018 27
4A Next Steps

28. Oct 17, 2018 28
4A Next Steps