/**********************************************************************
* RPi 3B Aduio 3.5mm output
* 说明：
* 看到树莓派上一个3.5mm耳机口，从来没用过，折腾一下。
*
* 2018-7-13 深圳 宝安西乡 曾剑锋
*********************************************************************/
一、参考文档：
1. 树莓派如何选择3.5mm耳机孔输出声音
https://jingyan.baidu.com/article/64d05a02220053de55f73bbc.html
二、具体操作：
1. sudo raspi-config
2. 选择流程：
Raspberry Pi 3 Model B Rev 1.2
┌─────────┤ Raspberry Pi Software Configuration Tool (raspi-config) ├──────────┐
│ │
│ 1 Change User Password Change password for the current u │
│ 2 Network Options Configure network settings │
│ 3 Boot Options Configure options for start-up │
│ 4 Localisation Options Set up language and regional sett │
│ 5 Interfacing Options Configure connections to peripher │
│ 6 Overclock Configure overclocking for your P │
│ 7 Advanced Options Configure advanced settings <---│
│ 8 Update Update this tool to the latest ve │
│ 9 About raspi-config Information about this configurat │
│ │
│ │
│ │
│ <Select> <Finish> │
│ │
└──────────────────────────────────────────────────────────────────────────────┘
┌─────────┤ Raspberry Pi Software Configuration Tool (raspi-config) ├──────────┐
│ │
│ A1 Expand Filesystem Ensures that all of the SD card s │
│ A2 Overscan You may need to configure oversca │
│ A3 Memory Split Change the amount of memory made │
│ A4 Audio Force audio out through HDMI or 3 <---│
│ A5 Resolution Set a specific screen resolution │
│ A6 Pixel Doubling Enable/Disable 2x2 pixel mapping │
│ A7 GL Driver Enable/Disable experimental deskt │
│ │
│ │
│ │
│ │
│ │
│ <Select> <Back> │
│ │
└──────────────────────────────────────────────────────────────────────────────┘
┌──────────────────────────────────────────────────────────┐
│ Choose the audio output │
│ │
│ 0 Auto │
│ 1 Force 3.5mm ('headphone') jack <--- │
│ 2 Force HDMI │
│ │
│ │
│ │
│ │
│ │
│ │
│ │
│ │
│ │
│ │
│ │
│ <Ok> <Cancel> │
│ │
└──────────────────────────────────────────────────────────┘
3. speaker-test -t sine
