How to connect to a device with 2 VCP using USB_HOST functionality

[KetanP]

I am using an STM32 Nucleo-64 F401RE6 and need to interface with a sensor that has a single physical USB port but appears as two Virtual COM ports on a PC. I have configured the Nucleo board in USB_OTG Host Only mode and successfully enumerated the device. However, the connection is established with only one of the COM ports.

How can I access data from both Virtual COM ports using USB Host mode on the Nucleo board?

[Pavel A.]

IIRC you only need to duplicate the data structure of the CDC host "class" driver to the second USB controller. This was not generated automatically in previous Cube versions, probably still is. Then it should work.

[KetanP]

Do you mean duplicating the entire chain,

MX_USB_HOST_Init()
MX_USB_HOST_Process() and so on?

[Pavel A.]

Apologies, I've misunderstood your case. It rather should be a composite device on one host controller. Can you confirm on the PC side that it is a composite device? Does it have only two CDC or more functions?

AFAIK there are no ST composite examples for host. The host program will need to read the 2nd function descriptor, find its endpoints and poll them together with the first function.

[KetanP]

1.) On PC the sensor shows up as 2 VCOM ports.

2.)  "The host program will need to read the 2nd function descriptor, find its endpoints and poll them together with the first function." Could you please elaborate, I am a beginner and finding it hard to understand the process.

The device enlists 7 Interfaces, Out of which 2 are CDC-ACM class interface ( Interface 1 and 3).

If I am not wrong, these 2 are used to read and write data by the sensor? On PC the devices lists as 

[239751.887813] cdc_acm 1-11.1:1.0: ttyACM1: USB ACM device
[239751.888010] cdc_acm 1-11.1:1.3: ttyACM2: USB ACM device

Since I only care about the second device, I set the phost->device.current_interface = 3;

Could you please confirm if this is the correct process?