The USB state machine of the control endpoint

UM0463

16/30

Recipient of endpoint

The library does not support the Halt feature for the endpoint 0. In the configured state, the

library checks if status register of the specified endpoint is not set as DISABLE (see

Section 1.2.1). Then the endpoint is set to STALL status (Set Feature) or is set to NAK

status if it was in the STALL status (Clear Feature.)

After the status of the endpoint is changed correctly, the user code implemented callback

function USER_USB_Clear_Feature_EP() is called for the Clear Feature request and the

USER_USB_Set_Feature_EP() is called for the Set Feature request. In

USER_USB_Clear_Feature_EP(), the user code knows that a STALL condition is cleared

for certain endpoint and it is up to the user code to set the endpoint to ACK or stay in NAK

status. In USER_USB_Set_Feature_EP(), the user code knows that a STALL condition is

set for certain endpoint so that the state machine of that endpoint can be paused or

stopped.

3.5.4

Set address

The library checks the parameters of the request and set the device to the new address if

the request is valid. There is no user code callback for this request.

3.5.5

Get descriptor

A structure is defined for the user code to pass the descriptors to the library.

typedef struct OneDescriptor {

char *Descriptor;

unsigned short Size;

} ONE_DESCRIPTOR;

The field Descriptor is the pointer that points to the descriptor and the field Size gives the

length of the descriptor.

An Application Descriptor table (Appli_Desc_Tab) is defined in the user area to keep track of

descriptors. The number of string descriptors in the table has to be configured by the user

through NUM_APP_STR_DESC macro (descriptor.h file) and the descriptor table has to be

changed accordingly. This descriptor table is accessed through a pointer variable

(DescTabPtr) which is present at a fixed location in the RAM. The user has to pass the

address of the table to this pointer (DescTabPtr) in his main (App_main) function. The rest

will be taken care of by the library.

supported. The remaining string descriptors will follow language ID descriptor in the

descriptor table.

Limitation: The library supports the language ID of US English (0x0409) only, so the element

0 of StringDescriptor should list one language ID of US English only.

Constant descriptors

A descriptor is constant if the descriptor is stored in a single continued data buffer when it is

going to be sent to the host. With the constant descriptors, the application initializes the

Descriptor table pointer with the table address. The library will send the constant descriptors

when they are required.