Topics and priorities
1 ) Networked audio devices - AVB
2 ) cross ECU interactions (remote control, including comparison with remote servers interaction)
3 ) Audio effects
Network Audio Synchronization
workshop 26/11/2020
- ECUs spread across a network have different clocks (CPU, network, audio,...)
- Clock drift, oscillators accuracy (1/day => 10 us/sec => for 44.1KHz one sample loss each 2 sec)
- Solution run SW on synchronized time
- how to synchronize time ?
- asynchronous resampling needed as the speakers DAC always need to be synchronous to their own clock
- PTP
- PTP does not solve jitter problem => how to compensate jitter ? => increase buffer size => increase latency
- Clock recovery. Or how to generate a clock when all we get from ptp is sporadic info about delay status + or -
- real-time accuracy vs latency
- TNS = Sync + Latency + Reliability, ... (SRP Stream Reservation Protocol)
- What if we cannot synchronize the time ?
- Mixing of different streaming sources (can't follow multiple clocks)
- Asynchronous resampling => latency
- Synchronous resampling (format conversion only for already synchronized clocks)
- AVB : Routing only => cable connection for a continuous audio stream => No control, no start, no pause, no skip,...
- AVB Software
- Kernel module (Steve => RENESAS_RCH3M3M3NE3_EAVB_AVBStreaming_UME_v2.00 page 5)
- (RENESAS_RCH3M3M3NE3_EAVB_LauncherApplication_ANE_v2.00 page 10)
- ALSA to AVB (RENESAS_RCH3M3M3NE3_EAVB_MSE_UME_v2.00 page 4)
- Existing open source AVB linux integrations (HW dependent topic)
References
| Clock drift | clock drift : Interaction of systems running on different clocks | |
|---|---|---|
| Clock recovery | PLL vs synchronization (ramping) | |
| Resampling | signal processing and resampling | |
| Avnu | low-latency, time-synchronized, highly reliable synchronized networked devices Avnu = AVB + TNS AVB = AV + PTP | |
| PTP | Precision Time Protocol | |
| Automotive AVB | Focus on subset of standards (features) | |
| 802.1 TNS | Time Sensitive Networking | |
| AVB on linux | Existing open source integrations |
Brainstorming
Use cases
1) external Amplifier, controlled by Android only (cross ECU interface used by headunit only)
2) interact of an Android Audio ECU with the rest of the audio system other ECUs (e.g. remote control - e.g. non Android system)
3) interact with the Audio System from a server
Relations to existing work in other SIG
CVII : Common Vehicle Interface Initiative
VSS : Vehicle Signal specification
VSC : Vehicle Service Catalogue (list of interfaces)
Audio and VSS, data interfaces,...
common model for data (call functions with params, services, interfaces, franca,...)
-no dealing with streaming data, rather simply connection points urls exchange
-can we define similar things to audio e.g. currently played track, volume,... ?
-requests to add media in VSS
-standardized interface for audio/media streaming, renewed interest by Hyundai
- complex question, OEM => standardize / Netflix => App custom standard
- if possible to add info in VSS
- different scope from cross ECU interfaces
-prevent fragmentation by collecting a survey about state of the art
- MPRIS dbus standard
1) Bluetooth : the AVRCP allows to control
2) Project Mode : / Audroid Auto - has virtual key input generator (volume up/down,...)
3) the same infrastructure from Project mode : can be used to inject the same as if it was a projected mode
4) Automotive : specific vehicle HAL service vehicle bus and converts in Android key codes
Android input system
Q: if volume key up/down limited to current volume ?
A: in automotive concept of volume groups which has the focus
Q: If the same interface include the audio settings
A: no intended in that interface
A: done through the audio effects HAL which is manufacturer specific
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mention as info : MQTT Pub/Sub mechanism
Remote topic split in two :
- play pause,...
- effects, calibration,...
_______________________________________________________
Q: What to develop next in the project
- Organization of the Android build
=> scripting the build ongoing, testing,...
Q: interest in AVB networked devices ?
- control / routing
- available AVB in automotive / professional audio
- https://github.com/Avnu/OpenAvnu
- Android (no many echos about AOSP/AVB)
- NXP/Renesas/ : board has AVB support
- Hikey 960 does not support AVB
- HW mandatory, not only low cost but automotive HW
- Android 11 support for Dragonboard
=> TODO organise an AVB introduction next week 26/11/2020
(TSN wider scope : https://en.wikipedia.org/wiki/Time-Sensitive_Networking)
Q: Any close to Android transport protocol or if it's part of the applications
A: usually part of the applications
A: approach interfacing Android system from outside like any Android app would do
=> CVII common standard initiative