STM32F207 USB driver

[xie]

Posted on November 18, 2014 at 08:26

Hello,

When I study the STM32F207 USB HOST MSC project, the free channel function index confuse me a lot.  Why the index in USBH_DeAllocate_AllChannel () starts from 2 not 0? In other function, the index is from 0 to 7.  The channel 0 and 1 can't be DeAllocate?

/**

  * @brief  USBH_DeAllocate_AllChannel   *         Free all USB host channel * @param  pdev : core instance   * @retval Status   */ uint8_t USBH_DeAllocate_AllChannel  (USB_OTG_CORE_HANDLE *pdev) {    uint8_t idx;       for (idx = 2; idx < HC_MAX ; idx ++) // Here is the index    {   pdev->host.channel[idx] = 0;    }    return USBH_OK; }

/**

  * @brief  USBH_GetFreeChannel   *         Get a free channel number for allocation to a device endpoint   * @param  None   * @retval idx: Free Channel number   */ static uint16_t USBH_GetFreeChannel (USB_OTG_CORE_HANDLE *pdev) {   uint8_t idx = 0;     for (idx = 0 ; idx < HC_MAX ; idx++)   {  if ((pdev->host.channel[idx] & HC_USED) == 0)  {     return idx;  }   }   return HC_ERROR; } #stm32f207-usb-dirver

[valen]

Posted on November 19, 2014 at 20:03

As I understand each host example allocates 2 channels as part of the host interface initialization code. These 2 channels supposed to stay alive during the live of the application. They are de allocated explicitly at the end of the application.   

USBH_DeAllocate_AllChannel is supposed to be called to free any other channels that were allocated to communicate with a device. It is called by the host when that device is detached.