Which Endpoint to send CBW in USB Host

[Jun]

hi,

I am working on USB Host project to read/write mass storage device.

I am confused on which Endpoint to send CBW. As per Bulk-only protocol explain, "The host shall send each CBW, which contains a command block, to the device via the Bulk-Out endpoint."--<Universal Serial Bus Mass Storage Class Bulk-Only Transport>.

For example, the Bulk-out Endpoint of my USB stick is Endpoint2. I send a CBW with Read Capacity command via endpoint2.
I can actually get a ACK for the CBW transfer, but I can't get TRNIF interrupt.

But when I read the Microchip's MLA-- USB Host -MSD-Data logger's code, it use endpoint0 to send the CBW. but endpoint2 buffer.

I am not sure where I got wrong. If we use Endpoint0 to send CBW and receive data, then what is the point to know which one is the bulk-out and bulk-in endpoint?

Thanks for your help.

Jun