STM32L55 USB microphone 4 channels using external I2S

[Dhanaraj]

Hi,

I have an external ADC connected to my STM32L55 using the I2S interface. The ADC is sampling 4-channel 16-bit data at 48000Hz sampling rate. However, I have encountered issues while streaming a large amount of data using USB CDC. Therefore, I am considering using the Audio device class to solve this problem. By doing so, I hope to make the PC recognize the 4 channels as 4 microphones and receive all the data without losing a single sample. I've configured my ADC as a master to ensure that there is always data for the STM32 to receive. 

To begin with, I plan to modify the USB descriptor so that the PC can recognize the STM32 as a microphone. My question is whether I need to make more changes than just altering the descriptor. Do I need to properly fill in these functions?

USBD_AUDIO_ItfTypeDef USBD_AUDIO_fops_FS =

{

AUDIO_Init_FS,

AUDIO_DeInit_FS,

AUDIO_AudioCmd_FS,

AUDIO_VolumeCtl_FS,

AUDIO_MuteCtl_FS,

AUDIO_PeriodicTC_FS,

AUDIO_GetState_FS,

};

[LCE]

I have never used USB audio class, but I would check a) where and when these might be called , and b) what the return values of these functions are, or what's done with pointers given to these functions.

Are there any example / __weak functions or prototypes?

[Dhanaraj]

After modifying the USB descriptor, my STM was neither detected as a speaker nor a Mic. I captured the USB description on the Windows side; the data is below. I am referring to this page for my changes (https://hackaday.io/project/181868-stm32f4-usb-microphone/details).

I think the windows error is due to an unsuccessful query by the OS. But not sure what OS wants that I need to implement in STM. I never got the data IN request from the OS. Can anyone point me what I am missing here.

USBD_AUDIO_DataIn

Information for device USB\Vendor_0483_Product_5740:

------------------------------
Connection Information:
------------------------------
Device current bus speed: FullSpeed
Device supports USB 1.1 specification
Device supports USB 2.0 specification
Device address: 0x0003
Current configuration value: 0x01
Number of open pipes: 0

------------------------------
Device Descriptor:
------------------------------
0x12 bLength
0x01 bDescriptorType
0x0201 bcdUSB
0x00 bDeviceClass
0x00 bDeviceSubClass
0x00 bDeviceProtocol
0x40 bMaxPacketSize0 (64 bytes)
0x0483 idVendor
0x5740 idProduct
0x0200 bcdDevice
0x01 iManufacturer
0x02 iProduct
0x03 iSerialNumber
0x01 bNumConfigurations

-------------------------
Configuration Descriptor:
-------------------------
0x09 bLength
0x02 bDescriptorType
0x0064 wTotalLength (100 bytes)
0x02 bNumInterfaces
0x01 bConfigurationValue
0x00 iConfiguration
0x80 bmAttributes (Bus-powered Device)
0x32 bMaxPower (100 mA)

Interface Descriptor:
------------------------------
0x09 bLength
0x04 bDescriptorType
0x00 bInterfaceNumber
0x00 bAlternateSetting
0x00 bNumEndPoints
0x01 bInterfaceClass (Audio Device Class)
0x01 bInterfaceSubClass (Audio Control Interface)
0x00 bInterfaceProtocol (Audio Protocol undefined)
0x00 iInterface

AC Interface Header Descriptor:
------------------------------
0x09 bLength
0x24 bDescriptorType
0x01 bDescriptorSubtype
0x0100 bcdADC
0x001E wTotalLength (30 bytes)
0x01 bInCollection
0x01 baInterfaceNr(1)

AC Input Terminal Descriptor:
------------------------------
0x0C bLength
0x24 bDescriptorType
0x02 bDescriptorSubtype
0x01 bTerminalID
0x0201 wTerminalType (Microphone)
0x00 bAssocTerminal
0x01 bNrChannels (1 channels)
0x0000 wChannelConfig
0x00 iChannelNames
0x00 iTerminal

AC Output Terminal Descriptor:
------------------------------
0x09 bLength
0x24 bDescriptorType
0x03 bDescriptorSubtype
0x03 bTerminalID
0x0101 wTerminalType (USB Streaming)
0x00 bAssocTerminal
0x02 bSourceID
0x00 iTerminal

Interface Descriptor:
------------------------------
0x09 bLength
0x04 bDescriptorType
0x01 bInterfaceNumber
0x00 bAlternateSetting
0x00 bNumEndPoints
0x01 bInterfaceClass (Audio Device Class)
0x02 bInterfaceSubClass (Audio Streaming Interface)
0x00 bInterfaceProtocol (Audio Protocol undefined)
0x00 iInterface

Interface Descriptor:
------------------------------
0x09 bLength
0x04 bDescriptorType
0x01 bInterfaceNumber
0x01 bAlternateSetting
0x01 bNumEndPoints
0x01 bInterfaceClass (Audio Device Class)
0x02 bInterfaceSubClass (Audio Streaming Interface)
0x00 bInterfaceProtocol (Audio Protocol undefined)
0x00 iInterface

AS Interface Descriptor:
------------------------------
0x07 bLength
0x24 bDescriptorType
0x01 bDescriptorSubtype
0x03 bTerminalLink
0x01 bDelay
0x0001 wFormatTag (PCM)

AS Format Type 1 Descriptor:
------------------------------
0x0B bLength
0x24 bDescriptorType
0x02 bDescriptorSubtype
0x01 bFormatType (FORMAT_TYPE_1)
0x01 bNrChannels (1 channels)
0x02 bSubframeSize
0x10 bBitResolution (16 bits per sample)
0x01 bSamFreqType (Discrete sampling frequencies)
0x00BB80 tSamFreq(1) (48000 Hz)

Endpoint Descriptor (Audio/MIDI 1.0):
------------------------------
0x09 bLength
0x05 bDescriptorType
0x81 bEndpointAddress (IN endpoint 1)
0x05 bmAttributes (Transfer: Isochronous / Synch: Asynchronous / Usage: Data)
0x0060 wMaxPacketSize (1 x 96 bytes)
0x01 bInterval (1 frames)
0x00 bRefresh
0x00 bSynchAddress

AS Isochronous Data Endpoint Descriptor:
------------------------------
0x07 bLength
0x25 bDescriptorType
0x01 bDescriptorSubtype
0x00 bmAttributes
0x00 bLockDelayUnits (undefined)
0x0000 wLockDelay

Microsoft OS Descriptor is not available. Error code: 0x0000001F

--------------------------------
String Descriptor Table
--------------------------------
Index LANGID String

------------------------------

Connection path for device:
USB xHCI Compliant Host Controller
Root Hub
Generic USB Hub
USB\Vendor_0483_Product_5740 Port: 4

Running on: Windows 10 or greater (Build Version 22621)

Brought to you by TDD v2.17.0, Feb 23 2021, 14:04:02