esp32s3: how to know usb interface altsetting?

[emard]

for esp32s3 dfu example I created descriptor that has two altsettings
alt=0 and alt=1

how to know from micropython, is there some variable of function
which returns currently used altsetting (value 0 or 1 in my case)

this is how descriptor looks from lsusb -v -d

Bus 001 Device 115: ID 1d50:614b OpenMoko, Inc. iProduct
Negotiated speed: Full Speed (12Mbps)
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass            0 [unknown]
  bDeviceSubClass         0 [unknown]
  bDeviceProtocol         0 
  bMaxPacketSize0        64
  idVendor           0x1d50 OpenMoko, Inc.
  idProduct          0x614b iProduct
  bcdDevice            1.00
  iManufacturer          17 iManufacturer
  iProduct               18 iProduct
  iSerial                19 iSerialNumber
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength       0x002d
    bNumInterfaces          1
    bConfigurationValue     1
    iConfiguration          0 
    bmAttributes         0x80
      (Bus Powered)
    MaxPower              100mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           0
      bInterfaceClass       254 Application Specific Interface
      bInterfaceSubClass      1 Device Firmware Update
      bInterfaceProtocol      2 
      iInterface             20 @FPGA/0x0/1024*4Ke
      Device Firmware Upgrade Interface Descriptor:
        bLength                             9
        bDescriptorType                    33
        bmAttributes                       13
          Will Detach
          Manifestation Tolerant
          Upload Unsupported
          Download Supported
        wDetachTimeout                    255 milliseconds
        wTransferSize                    4096 bytes
        bcdDFUVersion                   1.1a
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       1
      bNumEndpoints           0
      bInterfaceClass       254 Application Specific Interface
      bInterfaceSubClass      1 Device Firmware Update
      bInterfaceProtocol      2 
      iInterface             21 @FLASH/0x0/4096*4Ke
      Device Firmware Upgrade Interface Descriptor:
        bLength                             9
        bDescriptorType                    33
        bmAttributes                       13
          Will Detach
          Manifestation Tolerant
          Upload Unsupported
          Download Supported
        wDetachTimeout                    255 milliseconds
        wTransferSize                    4096 bytes
        bcdDFUVersion                   1.1a
Device Status:     0x0000
  (Bus Powered)

this is how dfu-util -l sees it

Found DFU: [1d50:614b] ver=0100, devnum=115, cfg=1, intf=0, path="1-3.1.2", alt=1, name="@FLASH/0x0/4096*4Ke", serial="iSerialNumber"
Found DFU: [1d50:614b] ver=0100, devnum=115, cfg=1, intf=0, path="1-3.1.2", alt=0, name="@FPGA/0x0/1024*4Ke", serial="iSerialNumber"

Now I need some hint how in the example
https://github.com/micropython/micropython/blob/master/examples/usb/usb_dfu_device.py

can I know which alt setting is being used?