*      
  *          ===================================================================      
  *                                 How to use this driver
  *          =================================================================== 
  *          1. Enable The DMA controller clock using CLK_PeripheralClockConfig() 
  *            function: CLK_PeripheralClockConfig(CLK_Peripheral_DMA1, ENABLE).
  *
  *          2. Enable and configure the peripheral to be connected to the DMA 
  *            channel (except for internal SRAM / FLASH memories: no 
  *            initialization is necessary). 
  *        
  *          3. For a given Channel, program the Source and Destination 
  *             addresses, the transfer Direction, the Buffer Size, the 
  *             Peripheral and Memory Incrementation mode and Data Size, 
  *             the Circular or Normal mode, the channel transfer Priority 
  *             and the Memory-to-Memory transfer mode (for channel 3 only, 
  *             if needed) using the DMA_Init() function.
  *
  *          4. Enable the the corresponding interrupt(s) using the function 
  *             DMA_ITConfig() if you need to use DMA interrupts. 
  *
  *          5. Enable the DMA channel using the DMA_Cmd() function. 
  *                
  *          6. Activate the needed channel Request using PPP_DMACmd() function 
  *            for any PPP peripheral except internal SRAM and FLASH (ie. TIM4, 
  *             USART ...). The function allowing this operation is provided in 
  *             each PPP peripheral driver (ie. TIM4_DMACmd for TIM4 peripheral).     
  *
  *          7. Optionally, you can configure the number of data to be 
  *             transferred when the channel is disabled (ie. after each 
  *             Transfer Complete event or when a Transfer Error occurs) using 
  *             the function DMA_SetCurrDataCounter().
  *             And you can get the number of remaining data to be transferred 
  *             using the function DMA_GetCurrDataCounter() at run time (when 
  *             the DMA channel is enabled and running).  
  *                   
  *          8. To control DMA events you can use one of the following 
  *              two methods:
  *               a- Check on DMA channel flags using the function 
  *                  DMA_GetFlagStatus().  
  *               b- Use DMA interrupts through the function DMA_ITConfig() 
  *                   at initialization phase and DMA_GetITStatus() function 
  *                   into interrupt routines in communication phase.  
  *              After checking on a flag you should clear it using 
  *              DMA_ClearFlag() function. And after checking on an interrupt 
  *              event you should clear it using DMA_ClearITPendingBit() 
  *              function.     
  *                 
  *