ds4蓝牙逆向工程：DS4-BT
ds4drv关于蓝牙音频传输的讨论：chrippa/ds4drv
较新的linux驱动中已经集成了ds4驱动，源码位置：
linux/drivers/hid/hid-sony.c
这里直接读取了linux准备好的/dev/input/js*设备，或者按照逆向工程读取report_id 11的内容。
TBD
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bluez与SBC编码
按照逆向工程的描述，ds4接收的是SBC编码的蓝牙音频，作为linux默认的蓝牙协议栈，bluez提供了SBC编解码API。
pi0的Debian系统可以直接apt安装
# apt install libsbc-dev请阅读bluez提供的例子，理解一下SBC编码原理与使用方法。
对于ds4来说，SBC音频头如下：
9c 75 19 24
0x9c = 156 syncword (always set to 156) 1 byte - sf bl cm a s (msb..lsb) * frequency: 00-16000 01-32000 10-44100 11-48000 * blocks: 00-4 01-8 10-12 11-16 * channels: 00-MONO 01-DUAL_CHANNEL 10-STEREO 11-JOINT_STEREO * allocation method: 0-loudnes 1-SNR * subbands: 0-4 1-8 1 byte - bitpool ...在例子中选择的SBC编码是
32kHz, 16blocks, 2channels, loudness, 8subbands,使用sbc_encode(...)时会生成对应音频头. -
定时发送
用于使用的是hidraw传输数据，我们要自行规划每次数据的传输间隔，保证在上一包音频数据消耗完时有下一包音频数据补充上。
对于"32kHz 8subbands"SBC编码后的数据来说，每一帧大小为：
frame_size = 4 + (4 * subbands * channels) / 8 +(blocks * channels * bitpool) / 8
=
4 + 4*8*2/8 + 16*2*25/8 = 112bytes每帧时间为：
frame_time = subbands * blocks / sample_rate
=
8*16/32 = 4msreport_14/15每包有2帧数据，耗时8ms；report_17/18/19每包有4帧数据，耗时16ms。理论上，我们只要每8ms或16ms发送一包数据即可。
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ALSA与PCM
在较新的linux内核中使用ALSA作为默认的音频框架，我们需要从ALSA读取PCM数据再交由SBC编码，最后通过蓝牙发送ds4。
这里使用libasound2读写声卡设备：
# apt install libasound2-dev需要注意的是，通过
snd_pcm_hw_params_get_period_size获取的PCM的帧数量，需要换算成字节数：frame_size = sample_bits * channels / 8
period_size = period_frames * frame_size对于SND_PCM_FORMAT_S16_BE双声道来说，每一帧大小为4bytes，SBC每帧大小为
sbc_get_codesize(...)=512bytes,编码后大小为sbc_encode(...)=112bytes,与ds4逆向工程提供的数据一致。
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设置pi0的UAC
pi0的Debian系统内核使用的是UAC2.0，如果需要连接Nintendo Switch作为USB音箱的话，需要编译成UAC1.0，请参考我的另一个项目pi-joystick。
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设置pi0的audio source
# pacmd list-sources > index: 1 name: <alsa_input.platform-20980000.usb.analog-stereo> driver: <module-alsa-card.c> flags: HARDWARE DECIBEL_VOLUME LATENCY DYNAMIC_LATENCY state: IDLE suspend cause: priority: 9009 volume: front-left: 65536 / 100% / 0.00 dB, front-right: 65536 / 100% / 0.00 dB balance 0.00 base volume: 65536 / 100% / 0.00 dB volume steps: 65537 muted: no current latency: 3945.43 ms max rewind: 0 KiB sample spec: s16le 2ch 48000Hz channel map: front-left,front-right Stereo used by: 0 linked by: 0 configured latency: 341.33 ms; range is 0.50 .. 341.33 ms card: 0 <alsa_card.platform-20980000.usb> module: 6 properties: alsa.resolution_bits = "16" device.api = "alsa" device.class = "sound" alsa.class = "generic" alsa.subclass = "generic-mix" alsa.name = "UAC2 PCM" alsa.id = "UAC2 PCM" alsa.subdevice = "0" alsa.subdevice_name = "subdevice #0" alsa.device = "0" alsa.card = "1" alsa.card_name = "UAC2_Gadget" alsa.long_card_name = "UAC2_Gadget 0" device.bus_path = "platform-20980000.usb" sysfs.path = "/devices/platform/soc/20980000.usb/gadget/sound/card1" device.string = "hw:1" device.buffering.buffer_size = "65536" device.buffering.fragment_size = "4096" device.access_mode = "mmap+timer" device.profile.name = "analog-stereo" device.profile.description = "Analog Stereo" device.description = "UAC2_Gadget Analog Stereo" module-udev-detect.discovered = "1" device.icon_name = "audio-card" ports: analog-input: Analog Input (priority 10000, latency offset 0 usec, available: unknown) properties: active port: <analog-input>看到pi0 gadget模拟的音频输入设备为
index: 1 , name: <alsa_input.platform-20980000.usb.analog-stereo>，接下来把它设置为默认信源。# pacmd set-default-source 1 -
pi0蓝牙连接ds4
推荐编译安装最新的bluez，较老的版本可能会出现一些莫名的错误。
# bluetoothctl -v > 5.9 # bluetoothctl [bluetooth]# power on [bluetooth]# agent on [bluetooth]# default-agent [bluetooth]# scan on Discovery started [CHG] Controller B8:27:**:**:**:** Discovering: yes [NEW] Device DC:0C:**:**:**:** Wireless Controller [bluetooth]# info DC:0C:**:**:**:** Device DC:0C:**:**:**:** Name: Wireless Controller Alias: Wireless Controller Class: 0x002508 Icon: input-gaming Paired: yes Trusted: yes Blocked: no Connected: no LegacyPairing: no UUID: Human Interface Device... (00001124-0000-1000-8000-00805f9b34fb) UUID: PnP Information (00001200-0000-1000-8000-00805f9b34fb) Modalias: usb:v054Cp09CCd0100 [bluetooth]# pair DC:0C:**:**:**:** Attempting to pair with DC:0C:**:**:**:** [CHG] Device DC:0C:**:**:**:** Connected: yes [CHG] Device DC:0C:**:**:**:** Modalias: usb:v054Cp09CCd0100 [CHG] Device DC:0C:**:**:**:** Modalias: usb:v054Cp09CCd0100 [CHG] Device DC:0C:**:**:**:** UUIDs has unsupported type [CHG] Device DC:0C:**:**:**:** Paired: yes Pairing successful [CHG] Device DC:0C:**:**:**:** Connected: no [CHG] Device DC:0C:**:**:**:** RSSI: -43 [bluetooth]# yes [bluetooth]# connet DC:0C:**:**:**:** Attempting to connect to DC:0C:**:**:**:** [CHG] Device DC:0C:**:**:**:** Connected: yes Connection successful [CHG] Device DC:0C:**:**:**:** Modalias: usb:v054Cp09CCd0100 [CHG] Device DC:0C:**:**:**:** Modalias: usb:v054Cp09CCd0100成功连接ds4后，ds4手柄会亮起蓝色氛围灯，pi0中新增hidraw设备。
# ls -al /dev/hidraw* > crw------- 1 root root 247, 0 4月 6 12:54 /dev/hidraw0 # chmod 666 /dev/hidraw0如果出现了什么问题，请考虑升级bluez。
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TBD