The USB state machine of the control endpoint

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For the Set Interface request, the user code in the USER_USB_Set_Interface() should take

the variable sUSB_vSetup.USBwIndex0 as the interface index and the variable

sUSB_vSetup.USBwValue0 as the alternative setting value. The user code validates these

two variables and configures the specified interface accordingly. The function

USER_USB_Set_Interface() returns REQ_ERROR if there is any error, otherwise returns

REQ_SUCCESS.

For the Get Interface request, the user code in the function USER_USB_Get_Interface()

should take the variable sUSB_vSetup.USBwIndex0 as the interface index and returns the

alternative setting value of the specified interface if there is no error. The user code calls

RequestError() if there is any error.

3.5.8

Status stage of the standard requests

As specified in Section 3.4.3, the callback functions USER_USB_Status_In() and

USER_USB_Status_Out() will be called respectively at the end of all the standard requests

except Set Address request. In these two callback functions, the user code is able to know

what request is processed in the library.

3.6

The execution of the state machine

The state machine is in the state Wait_Setup when it is in idle. Once a SETUP packet is

received, the request is copied to the sUSB_vSetup structure and the field

sUSB_vSetup.flag is evaluated. Then the state machine is started. Figure 2 illustrates the

execution of the state machine. The state machine returns to the idle state (Wait_Setup)

after USER_USB_Status_In() or USER_USB_Status_Out() returns.As stated in

Section 2.1, the state machine of the control endpoint has two execution models: the polling

model and the interrupt model. Since all callback functions specified in this chapter are part

of the state machine, they can be part of the interrupt process routine if the state machine is

working in the interrupt model. The application developers have to be aware that there are

some limitations concerning writing code of the interrupt routines. This topic is not the scope

of this document; please refer to other documents for this issue.