USB stacks - can somebody explain?

[leesp]

I am beginning to learn how USB is implemented in MC9S08JM32. I was reading thru the code but couldn't quite understand it: the codes are pasted as follows.

What is the purpose of USB_Class_Init() and USB_Class_Hid_Event()?

uint_8 USB_Class_HID_Init (    uint_8    controller_ID,                /* [IN] Controller ID */    USB_CLASS_CALLBACK hid_class_callback,  /* [IN] HID Class Callback */    USB_REQ_FUNC       vendor_req_callback, /* [IN] Vendor Request Callback */    USB_CLASS_SPECIFIC_HANDLER_FUNC param_callback                                        /* [ IN] HID Class requests Callback */){    uint_8 index;    USB_ENDPOINTS *ep_desc_data = (USB_ENDPOINTS *)        USB_Desc_Get_Endpoints(controller_ID);    /* Initialize the device layer*/    uint_8 status = USB_Device_Init(controller_ID,        (uint_8)(ep_desc_data->count+1));    if(status == USB_OK)    {        /* Initialize the generic class functions */        status = USB_Class_Init(controller_ID,USB_Class_Hid_Event,            USB_Other_Requests);        if(status == USB_OK)        {            g_hid_endpoint_data.count = ep_desc_data->count;            for(index = 0; index < ep_desc_data->count; index++)            {                g_hid_endpoint_data.ep[index].endpoint =                    ep_desc_data->ep[index].ep_num;                g_hid_endpoint_data.ep[index].type =                    ep_desc_data->ep[index].type;                g_hid_endpoint_data.ep[index].bin_consumer = 0x00;                g_hid_endpoint_data.ep[index].bin_producer = 0x00;            }            /* save the HID class callback pointer */            g_hid_class_callback = hid_class_callback;            /* save the vendor request callback pointer */            g_vendor_req_callback = vendor_req_callback;            /* Save the callback to ask application for class specific params*/            g_param_callback = param_callback;        }    }    return status;}

uint_8 USB_Class_Init (    uint_8    controller_ID,                /* [IN] Controller ID */    USB_CLASS_CALLBACK class_callback,      /* [IN] Class Callback */    USB_REQ_FUNC       other_req_callback   /* [IN] Other Requests Callback */){    uint_8 status = USB_Framework_Init(controller_ID,class_callback,        other_req_callback);    /* save callback address */    g_class_callback = class_callback;    if(status == USB_OK)    {        /* Register all the services here */        status |= USB_Device_Register_Service(controller_ID,             USB_SERVICE_BUS_RESET, USB_Reset_Service);        status |= USB_Device_Register_Service(controller_ID,             USB_SERVICE_SOF,USB_Sof_Service);        status |= USB_Device_Register_Service(controller_ID,             USB_SERVICE_SLEEP,USB_Suspend_Service);        status |= USB_Device_Register_Service(controller_ID,             USB_SERVICE_RESUME,USB_Resume_Service);        status |= USB_Device_Register_Service(controller_ID,             USB_SERVICE_STALL,USB_Stall_Service);        status |= USB_Device_Register_Service(controller_ID,             USB_SERVICE_ERROR,USB_Error_Service);        /* set the device state as powered */        (void)USB_Device_Set_Status(controller_ID,             USB_STATUS_DEVICE_STATE,USB_STATE_POWERED);        g_device_state_before_suspend = USB_STATE_POWERED;    }    return status;}

static void USB_Class_Hid_Event (    uint_8 controller_ID,   /* [IN] Controller ID */    uint_8 event,           /* [IN] Event Type */    void* val               /* [IN] Pointer to configuration Value */){    uint_8 index;    if(event == USB_APP_ENUM_COMPLETE)    {        uint_8 count;        /* get the endpoints from the descriptor module */        USB_ENDPOINTS *ep_desc_data = (USB_ENDPOINTS *)            USB_Desc_Get_Endpoints(controller_ID);                             count = ep_desc_data->count;   /* deinitialize all endpoints in case they were initialized */  while(count > 0)   {      USB_EP_STRUCT_PTR ep_struct_ptr=     (USB_EP_STRUCT_PTR) (&ep_desc_data->ep[count - 1]);   (void)USB_Device_Deinit_EndPoint(controller_ID,    ep_struct_ptr->ep_num, ep_struct_ptr->direction);    count--;     }        /* intialize all non control endpoints */        while(count < ep_desc_data->count)        {            USB_EP_STRUCT_PTR ep_struct=                (USB_EP_STRUCT_PTR)&ep_desc_data->ep[count];            (void)USB_Device_Init_EndPoint(controller_ID, ep_struct, TRUE);            /* register callback service for the endpoint */            (void)USB_Device_Register_Service(controller_ID,                                  (uint_8)(USB_SERVICE_EP0+ep_struct->ep_num),                                                             USB_Service_Hid);            /* set the EndPoint Status as Idle in the device layer */            (void)USB_Device_Set_Status(controller_ID,                (uint_8)(USB_STATUS_ENDPOINT | (HID_ENDPOINT + (ep_struct->ep_num - 1)) |                (ep_struct->direction << USB_COMPONENT_DIRECTION_SHIFT)),                USB_STATUS_IDLE);            count++;        }    }    else if(event == USB_APP_BUS_RESET)    {        /* clear producer and consumer on reset */        for(index = 0; index < g_hid_endpoint_data.count; index++)        {            g_hid_endpoint_data.ep[index].bin_consumer = 0x00;            g_hid_endpoint_data.ep[index].bin_producer = 0x00;        }    }    if(g_hid_class_callback != NULL)    {        /* notify the application of the event */        g_hid_class_callback(controller_ID, event, val);    }}

[Tsuneo]

I don't know who made this one, but a horrible implementation.
He want to introduce layered architecture to the USB device stack, and failed. Processes which should be placed in a lower layer are spilled out into upper layer. 90% of this code is useless. Most of the code is there just to maintain his layered architecture. It does nothing useful for real USB implementation. This is a typical case, in which half-baked understanding makes things more complicated. Trash them all. It makes you confused.

The source code in CMX_USB-LITE is much better than this one. You'll get better perspective with this one.

http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=CMX_USB-LITE

Tsuneo

[leesp]

Thanks Tsuneo..

I believe these codes are supplied by Freescale.

I have a really hard time understanding the codes