UM0290 datasheet(21/76 Pages) STMICROELECTRONICS

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UM0290

STR7/STR9 USB firmware library

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1.4

Implementing a USB application using the STR7/9 USB

library

1.4.1

Implementing a no data class specific request

All class-specific requests without a data transfer phase implement the field

RESULT (*Class_NoData_Setup)(BYTE RequestNo)

of the structure device property.

The USBbRequest of the request is available in the parameter RequestNo and all other

request fields are stored in the device info structure.

The user has to implement the test of all request fields. If the request is compliant with the

class to implement the function must return the USB_SUCCESS result. However if there is

any problem in the request the function returns the status UNSUPPORT result and the

library responds with a STALL handshake.

1.4.2

How to implement a data class specific request

In the event of class requests requiring a data transfer phase, the user implementation

reports to the USB library the length of the data to transfer and the data location in the

internal memory (RAM in case of receiving the data from the host and RAM or Flash in case

of sending data to the host). This type of request is managed in the function

RESULT

(*Class_NoData_Setup)(BYTE

RequestNo)

. The user has to create for

each class data request a specific function with the format:

u8* My_First_Data_Request (u16 Length)

If this function is called with the parameter Length equal to zero, it sets the

pInformation->Ctrl_Info.Usb_wLength

field with the length of data to transfer and

return a NULL pointer. In other cases it returns the address of the data to transfer. The

following C code shows a simple example:

u8* My_First_Data_Request (u16 Length)

{

if (Length == 0)

{

pInformation->Ctrl_Info.Usb_wLength

= My_Data_Length;

return NULL;

}

else

return (&My_Data_Buffer);

}

The function RESULT (*Class_NoData_Setup)(BYTE RequestNo) manages all data

requests as described in the following C code:

RESULT Class_Data_Setup(u8 RequestNo)

{

u8 *(*CopyRoutine)(u16);

CopyRoutine = NULL;

if (My_First_Condition)// test the filds of the first request

CopyRoutine = My_First_Data_Request;

else if(My_Second_Condition) // test the filds of the second request

CopyRoutine = My_Second_Data_Request;

...

same implementation for each class data requests

...

if (CopyRoutine == NULL) return USB_UNSUPPORT;

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