PCM5122 DAC 与 Android Things

Question

我有一个使用 PCM5122 DAC 的 Raspberry Pi 3B 和 Suptronics X920 Expansion Board。所以我无法通过该板播放声音。

配置文件是默认的，除了显示配置部分：

kernel=u-boot-dtok.bin
framebuffer_depth=16

# Prevent the firmware from loading HAT overlays now that we handle pin muxing.
# ourselves. See:
# https://www.raspberrypi.org/documentation/configuration/device-tree.md#part3.4
dtoverlay=

dtparam=i2c_arm=on
dtparam=spi=on
dtparam=audio=on

# pwm and I2S are mutually-exclusive since they share hardware clocks.
dtoverlay=pwm-2chan-with-clk,pin=18,func=2,pin2=13,func2=4
dtoverlay=generic-i2s

start_x=1

# Tell U-boot to always use the "serial0" interface for the console, which is
# set to whichever uart (uart0 or uart1) is set to the header pins. This doesn't
# interfere with the uart selected for Bluetooth.
dtoverlay=chosen-serial0

# Enable skip-init on the UART interfaces, so U-Boot doesn't attempt to
# re-initialize them.
dtoverlay=rpi-uart-skip-init

# Add pin devices to the system for use by the runtime pin configuration driver.
dtoverlay=runtimepinconfig
dtoverlay=uart1
dtoverlay=bcm2710-rpi-3-b-spi0-pin-reorder

# Tell the I2S driver to use the cprman clock.
dtoverlay=bcm2710-rpi-3-b-i2s-use-cprman

# Uncomment to disable serial port on headers, use GPIO14 and GPIO15
# as gpios and to allow the core_freq to change at runtime.
enable_uart=1
core_freq=400

# Support official RPi display.
dtoverlay=i2c-rtc,ds3231
dtoverlay=rpi-ft5406
hdmi_force_hotplug=1

# Set framebuffer to support RGBA colors.
framebuffer_swap=0

# Waveshare display settings
max_usb_current=1
hdmi_group=2
hdmi_mode=87
hdmi_cvt 1024 600 60 6 0 0 0
hdmi_drive=1

这是播放声音文件的代码：

fun playSound(file: File) {
    val audioEncoding = AudioFormat.ENCODING_PCM_16BIT
    val sampleRate = 16000

    val audioOutputFormat = AudioFormat.Builder()
            .setChannelMask(AudioFormat.CHANNEL_OUT_MONO)
            .setEncoding(audioEncoding)
            .setSampleRate(16000)
            .build()

    val audioOutputBufferSize = AudioTrack.getMinBufferSize(sampleRate, audioOutputFormat.channelMask, audioEncoding)

    val audioOutputDevice = findAudioDevice(AudioManager.GET_DEVICES_OUTPUTS, AudioDeviceInfo.TYPE_BUS)

    val audioTrack = AudioTrack.Builder()
            .setAudioFormat(audioOutputFormat)
            .setBufferSizeInBytes(audioOutputBufferSize)
            .setTransferMode(AudioTrack.MODE_STREAM)
            .build()

    audioTrack.preferredDevice = audioOutputDevice

    val buffer = ByteArray(audioOutputBufferSize)

    audioTrack.play()
    audioTrack.setVolume(1f)

    val stream = file.inputStream().buffered()
    try {
        while (stream.read(buffer) > 0) {
            val out = audioTrack.write(buffer, 0, buffer.size, AudioTrack.WRITE_BLOCKING)
            d { "audioTrack.write = $out" }
        }
    } catch (error: Throwable) {
        e(error) { "Error playing audio $file" }
    } finally {
        stream.close()
    }

    audioTrack.stop()
    audioTrack.release()
}

private fun findAudioDevice(deviceFlag: Int, deviceType: Int): AudioDeviceInfo? {
    val manager = getSystemService(Context.AUDIO_SERVICE) as AudioManager
    val adis = manager.getDevices(deviceFlag)
    for (adi in adis) {
        if (adi.type == deviceType) {
            return adi
        }
    }
    return null
}

我已经用常规的 Raspberry Pi 音频输出（AudioDeviceInfo.TYPE_BUILTIN_SPEAKER）测试了代码，它工作正常。但是使用AudioDeviceInfo.TYPE_BUS，它只会产生没有任何错误的声音。

我尝试了各种配置选项，例如 dtoverlay=hifiberry 或 dtoverlay=hifiberry-dacplus，但没有成功。

请帮忙。

Answer 1

看起来您可能正在使用 Google Assistant sample 的某些代码，并且您正确地假设 TYPE_BUS 是启用音频路由以使用 I2S 总线而不是内置的音频插孔。

但是，这可能不是故事的全部。 DAC 可能需要额外的配置命令和/或外部触发器。例如，查看similar HAT with the same DAC，还有一个用于 DAC 设置命令的 I2C 总线连接。我们的 Assistant 示例使用 VoiceHAT driver 来完成该外设上的 DAC 所需的额外触发。

在 Raspbian 中，您通过 dtoverlay 启用的驱动程序可能会处理这两个部分。在这里，您的代码将需要手动管理设置位。看看 VoiceHAT 驱动程序是如何在 Assistant 示例中使用的。

另外，请确保您没有将任何 I2S 引脚启用为 GPIO 或 PWM，因为这将禁用音频路由 per the documentation。

旁注：Android Things 不支持通过config.txt 进行内核更改，因此在那里添加驱动程序预计不会有任何影响。

Answer 2

自从我弄清楚这一点以来已经有一段时间了，所以我发布了对我有用的代码，以便其他人花更少的时间埋在手册上。

在我花了几个小时阅读manual 并对电路板的原理图皱眉之后，我发现 PCM5122 芯片需要一些预配置。

事实证明，该芯片具有复杂的时钟方案。来自数据表：

串行音频接口通常有 4 个连接：SCK（系统主时钟）、BCK（位时钟）、LRCK（左 右字时钟）和DIN（数据）。该器件有一个内部 PLL，用于接收 SCK 或 BCK 和 创建内插处理器和 DAC 时钟所需的更高速率时钟。这允许设备 在有或没有外部 SCK 的情况下运行。

所以，长话短说，芯片的 PLL 操作取决于物理连接到 Raspberry 板的引脚 - SCK、BCK 或两者：

就我而言，它是 BCK。我们需要选择第 13 个寄存器的 PLL 时钟源：

解释完所有内容后，我将发布我使用过的完整驱动程序和一些额外的配置。您可以在链接的手册中找到所有信息。希望对您有所帮助。

class SuptronicsX920AudioDevice private constructor(
        private val busDevice: AudioDeviceInfo,
        private val i2cDevice: I2cDevice) : AudioDevice {

    private var audioTrack: AudioTrack? = null
    private var leftVolume = 1f
    private var rightVolume = 1f

    companion object {
        private const val ERROR_DETECT_REG = 37
        private const val ERROR_DETECT_IDCM_BIT = 3
        private const val PLL_SOURCE_REG = 13
        private const val PLL_SOURCE_BCK_BIT = 4
        private const val AUTO_MUTE_REG = 65
        private const val DIGITAL_VOLUME_LEFT_REG = 61
        private const val DIGITAL_VOLUME_RIGHT_REG = 62

        fun create(busDevice: AudioDeviceInfo, i2cDevice: I2cDevice): Either<IOException, SuptronicsX920AudioDevice> {
            return try {
                // Ignore BCK\SCK missing errors as they turn device into Power down mode
                riseRegBit(i2cDevice, ERROR_DETECT_REG, ERROR_DETECT_IDCM_BIT)

                // Select BCK as the source for PLL
                riseRegBit(i2cDevice, PLL_SOURCE_REG, PLL_SOURCE_BCK_BIT)

                // Disable auto mute for both channels
                i2cDevice.writeRegByte(AUTO_MUTE_REG, 0)

                // Set the maximum gain for both channels
                i2cDevice.writeRegByte(DIGITAL_VOLUME_LEFT_REG, 0)
                i2cDevice.writeRegByte(DIGITAL_VOLUME_RIGHT_REG, 0)

                SuptronicsX920AudioDevice(busDevice, i2cDevice).right()
            } catch (ioe: IOException) {
                e(ioe) { "Unable to configure PCM512x for Suptronics x920" }
                ioe.left()
            }
        }

        private fun riseRegBit(i2cDevice: I2cDevice, regAddress: Int, bitAddress: Int) {
            val value = i2cDevice.readRegByte(regAddress)
            i2cDevice.writeRegByte(regAddress, value or (1 shl bitAddress).toByte())
        }
    }

    override fun play(stream: InputStream, audioFormat: AudioFormat) {
        val audioOutputBufferSize = AudioTrack.getMinBufferSize(
                audioFormat.sampleRate,
                audioFormat.channelMask,
                audioFormat.encoding)
        val buffer = ByteArray(audioOutputBufferSize)

        audioTrack = AudioTrack.Builder()
                .setAudioFormat(audioFormat)
                .setBufferSizeInBytes(audioOutputBufferSize)
                .setTransferMode(AudioTrack.MODE_STREAM)
                .build()
        audioTrack?.apply {
            preferredDevice = busDevice

            setStereoVolume(leftVolume, rightVolume)
            play()

            var bytes = 0
            try {
                while (stream.read(buffer) > 0) {
                    bytes += write(buffer, 0, buffer.size, AudioTrack.WRITE_BLOCKING)
                }
            } catch (error: Throwable) {
                e(error) { "Error playing audio" }
            }
            d { "$bytes of audio track written" }
        }
        stop()
        audioTrack = null
    }

    override fun stop() {
        audioTrack?.apply {
            if (state != AudioTrack.STATE_UNINITIALIZED) {
                try {
                    pause()
                    flush()
                    release()
                    d { "Audio stopped" }
                } catch (error: Throwable) {
                    e(error) { "Can't stop track properly" }
                }
            }
        }
    }

    override fun setVolume(leftVolume: Float, rightVolume: Float) {
        this.leftVolume = leftVolume
        this.rightVolume = rightVolume
        audioTrack?.apply { setStereoVolume(leftVolume, rightVolume) }
    }

    override fun close() {
        stop()
        i2cDevice.close()
    }
}