Standard USB requests are processed by usb_sm_ctrl subprogram in usb.asm file. This subprogram identifies request type and the calls the corresponding handler. Bootloader supports standard USB requests, described in USB and HID specifications.
Bootloader uses HID interface to interact with PC software. HID transactions processing is described in the section called “HID transactions”.
All standard USB requests host sends to Endpoint 0. Bootloader processes the following USB requests: