I'm implementing a Virtual COM port on an STM32F4 MCU.
The MCU don't have endpoints left available so I have to revome interupt endpoint/notification element. The problem is the MCU can send a message to the pc only once, after the pc will not get it.
The device USB descriptor:
Interface Association Descriptor:
------------------------------
0x08 bLength
0x0B bDescriptorType
0x02 bFirstInterface
0x02 bInterfaceCount
0x02 bFunctionClass (Communication Device Class)
0x02 bFunctionSubClass (Abstract Control Model)
0x01 bFunctionProtocol (ITU-T V.250)
0x06 iFunction
Interface Descriptor:
------------------------------
0x09 bLength
0x04 bDescriptorType
0x02 bInterfaceNumber
0x00 bAlternateSetting
0x00 bNumEndPoints
0x02 bInterfaceClass (Communication Device Class)
0x02 bInterfaceSubClass (Abstract Control Model)
0x01 bInterfaceProtocol (ITU-T V.250)
0x02 iInterface ""
CDC Header Functional Descriptor:
------------------------------
0x05 bFunctionalLength
0x24 bDescriptorType
0x00 bDescriptorSubtype
0x0110 bcdCDC
CDC Call Management Functional Descriptor:
------------------------------
0x05 bFunctionalLength
0x24 bDescriptorType
0x01 bDescriptorSubtype
0x00 bmCapabilities
0x01 bDataInterface
CDC Abstract Control Management Functional Descriptor:
------------------------------
0x04 bFunctionalLength
0x24 bDescriptorType
0x02 bDescriptorSubtype
0x02 bmCapabilities
CDC Union Functional Descriptor:
------------------------------
0x05 bFunctionalLength
0x24 bDescriptorType
0x06 bDescriptorSubtype
0x00 bControlInterface
0x01 bSubordinateInterface(0)
Interface Descriptor:
------------------------------
0x09 bLength
0x04 bDescriptorType
0x03 bInterfaceNumber
0x00 bAlternateSetting
0x02 bNumEndPoints
0x0A bInterfaceClass (CDC Data)
0x00 bInterfaceSubClass
0x00 bInterfaceProtocol
0x02 iInterface ""
Endpoint Descriptor:
------------------------------
0x07 bLength
0x05 bDescriptorType
0x03 bEndpointAddress (OUT Endpoint)
0x02 bmAttributes (Transfer: Bulk / Synch: None / Usage: Data)
0x0010 wMaxPacketSize (16 Bytes)
0x00 bInterval
Endpoint Descriptor:
------------------------------
0x07 bLength
0x05 bDescriptorType
0x85 bEndpointAddress (IN Endpoint)
0x02 bmAttributes (Transfer: Bulk / Synch: None / Usage: Data)
0x0010 wMaxPacketSize (16 Bytes)
0x00 bInterval
If i remove this useless endpoint the usbser windows driver go nuts. So You have to have an interupt IN endpoint even if the application never ever use it.