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IAD descriptor issue in Keil USB Custom Class

Leo Cheng

Hello,

I am working on USB Video Class in LPC4357 with Keil Middleware 7.1.0(should be latest). I came across a problem about Video Interface Association Descriptor(IAD).

The bFunctionSubClass of IAD Descriptor is the same as bFunctionSubClass of interface 0 in Middleware 7.1.0 from the source code in usbd_config_desc_macros.h

  /* USB Device Custom Class n Interface Association Descriptor */
#define USBD_CUSTOM_CLASSn_IAD(n)            /* Interface Association Descriptor */\ 
  USB_INTERFACE_ASSOC_DESC_SIZE,             /* bLength */                         \ 
  USB_INTERFACE_ASSOCIATION_DESCRIPTOR_TYPE, /* bDescriptorType */                 \ 
  USBD_CUSTOM_CLASS##n##_IF0_NUM,            /* bFirstInterface */                 \ 
  USBD_CUSTOM_CLASS##n##_IF_CNT,             /* bInterfaceCount */                 \ 
  USBD_CUSTOM_CLASS##n##_IF0_CLASS,          /* bFunctionClass */                  \ 
  USBD_CUSTOM_CLASS##n##_IF0_SUBCLASS,       /* bFunctionSubclass */               \ 
  USBD_CUSTOM_CLASS##n##_IF0_PROTOCOL,       /* bFunctionProtocol */               \ 
  USBD_CUSTOM_CLASS##n##_IF0_STR_IDX,        /* iFunction */

But the bFunctionSubClass of Video IAD Descriptor should be different from the bFunctionSubClass of Video Control Interface Descriptor(interface 0). This results in an error reported by Microsoft USB Device Viewer.

  ===>IAD Descriptor<===
bLength:                           0x08
bDescriptorType:                   0x0B
bFirstInterface:                   0x00
bInterfaceCount:                   0x02
bFunctionClass:                    0x0E  -> Video Interface Class
bFunctionSubClass:                 0x01
*!*ERROR:    This should be USB_VIDEO_SC_VIDEO_INTERFACE_COLLECTION 3
bFunctionProtocol:                 0x00  -> PC_PROTOCOL_UNDEFINED protocol
iFunction:                         0x04
     English (United States)  "USB_CUSTOM_CLASS0_IF0"

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