Data Counter functions
[DMA_Private_Functions]

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                      ##### Data Counter functions #####
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    This subsection provides function allowing to configure and read the buffer size
    (number of data to be transferred). 
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    The DMA data counter can be written only when the DMA Stream is disabled 
    (ie. after transfer complete event).
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    The following function can be used to write the Stream data counter value:
      (+) void DMA_SetCurrDataCounter(DMA_Stream_TypeDef_mort* DMAy_Streamx, uint16_t Counter);
      -@- It is advised to use this function rather than DMA_Init() in situations 
          where only the Data buffer needs to be reloaded.
      -@- If the Source and Destination Data Sizes are different, then the value 
          written in data counter, expressing the number of transfers, is relative 
          to the number of transfers from the Peripheral point of view.
          ie. If Memory data size is Word, Peripheral data size is Half-Words, 
          then the value to be configured in the data counter is the number 
          of Half-Words to be transferred from/to the peripheral.
    [..]
    The DMA data counter can be read to indicate the number of remaining transfers for
    the relative DMA Stream. This counter is decremented at the end of each data 
    transfer and when the transfer is complete: 
      (+) If Normal mode is selected: the counter is set to 0.
      (+) If Circular mode is selected: the counter is reloaded with the initial value
          (configured before enabling the DMA Stream)
     [..]
     The following function can be used to read the Stream data counter value:
       (+) uint16_t DMA_GetCurrDataCounter(DMA_Stream_TypeDef_mort* DMAy_Streamx);