How to add endpoint to a vendor specific interface in CX3.

[mapper]

Hello,

I'm working my way through how the UVC descriptor structure works, so I will be thrilled to get details on the solution. 

I'm trying to create a vendor specific interface. I have followed this https://community.infineon.com/t5/Knowledge-Base-Articles/Vendor-Interface-in-UVC-KBA218335/ta-p/247... and I was successful to create the interface:

$usb-devices

T: Bus=04 Lev=03 Prnt=04 Port=00 Cnt=01 Dev#= 17 Spd=5000 MxCh= 0
😧 Ver= 3.00 Cls=ef(misc ) Sub=02 Prot=01 MxPS= 9 #Cfgs= 1
P: Vendor=04b4 ProdID=00c3 Rev=00.00
S: Manufacturer=Cypress
S: Product=CX3-UVC
C: #Ifs= 3 Cfg#= 1 Atr=c0 MxPwr=96mA
I: If#= 0 Alt= 0 #EPs= 1 Cls=0e(video) Sub=01 Prot=00 Driver=uvcvideo
I: If#= 1 Alt= 0 #EPs= 1 Cls=0e(video) Sub=02 Prot=00 Driver=uvcvideo
I: If#= 2 Alt= 0 #EPs= 0 Cls=ff(vend.) Sub=00 Prot=00 Driver=usbfs

In Ubuntu, I'm using a python application to send commands to this vendor specific interface. My application can also see this interface, as can be seen in the output below:

INTERFACE 2: Vendor Specific ===========================
bLength : 0x9 (9 bytes)
bDescriptorType : 0x4 Interface
bInterfaceNumber : 0x2
bAlternateSetting : 0x0
bNumEndpoints : 0x0
bInterfaceClass : 0xff Vendor Specific
bInterfaceSubClass : 0x0
bInterfaceProtocol : 0x0
iInterface : 0x0

But I can't write anything to this interface, as it doesn't have an endpoint. I tried simply increasing the number of endpoints in the interface descriptor:

0x09, /* Descriptor size */

CY_U3P_USB_INTRFC_DESCR, /* Interface descriptor type */

0x02, /* Interface number */

0x00, /* Alternate setting number */

0x01, /* Number of end points */

0xFF, /* Interface class */

0x00, /* Interface sub class */

0x00, /* Interface protocol code */

0x00 /* Interface descriptor string index */

This doesn't work. I believe I need to add the endpoint descriptor as well. I don't understand the structure, could you help describe how to add the endpoint to this specific vendor-specific interface that I have added?

I appreciate any help,

Kind regards,

Renato

[Rashi_Vatsa · Accepted solution]

Hello Renato,

You can refer to the firmware in AN75779 (An75779.zip) which has a provision to add vendor interface to UVC device by enabling USB_DEBUG_INTERFACE macro.

 ,
        0x09,                           /* Descriptor size */
        CY_U3P_USB_INTRFC_DESCR,        /* Interface Descriptor type */
        0x02,                           /* Interface number */
        0x00,                           /* Alternate setting number */
        0x02,                           /* Number of end points */
        0xFF,                           /* Interface class */
        0x00,                           /* Interface sub class */
        0x00,                           /* Interface protocol code */
        0x00,                           /* Interface descriptor string index */

        /* Endpoint descriptor for producer EP */
        0x07,                           /* Descriptor size */
        CY_U3P_USB_ENDPNT_DESCR,        /* Endpoint descriptor type */
        CY_FX_EP_DEBUG_CMD,             /* Endpoint address and description */
        CY_U3P_USB_EP_BULK,             /* Bulk endpoint type */
        0x00,0x04,                      /* Max packet size = 1024 bytes */
        0x00,                           /* Servicing interval for data transfers : 0 for bulk */
    
        /* Super speed endpoint companion descriptor for producer EP */
        0x06,                           /* Descriptor size */
        CY_U3P_SS_EP_COMPN_DESCR,       /* SS endpoint companion descriptor type */
        0,                              /* No burst support. */
        0x00,                           /* Max streams for bulk EP = 0 (No streams) */
        0x00,0x00,                      /* Service interval for the EP : 0 for bulk */
    
        /* Endpoint descriptor for consumer EP */
        0x07,                           /* Descriptor size */
        CY_U3P_USB_ENDPNT_DESCR,        /* Endpoint descriptor type */
        CY_FX_EP_DEBUG_RSP,             /* Endpoint address and description */
        CY_U3P_USB_EP_BULK,             /* Bulk endpoint type */
        0x00,0x04,                      /* Max packet size = 1024 bytes */
        0x00,                           /* Servicing interval for data transfers : 0 for Bulk */
    
        /* Super speed endpoint companion descriptor for consumer EP */
        0x06,                           /* Descriptor size */
        CY_U3P_SS_EP_COMPN_DESCR,       /* SS endpoint companion descriptor type */
        0,                              /* No burst support. */
        0x00,                           /* Max streams for bulk EP = 0 (No streams) */
        0x00,0x00                       /* Service interval for the EP : 0 for bulk */

Please note that modifying  /* Length of this descriptor and all sub descriptors*/  will be important after adding endpoint descriptors to the structure.

Please track the changes done to the AN75779 after enabling USB_DEBUG_INTERFACE to understand the changes needed to add an endpoint to an interface.

[mapper]

Hello Rashi,

Thank you for the answer. 

Indeed, I was missing a few steps to make it work. After adding the DMA channels and following the steps in AN75779, I was able to implement the vendor-specific command successfully.

Best regards, 

Renato