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1. This function will be called every time the device is opened.
2. Several aspects of SPI communication may need to be configured, including:
   a.
   • Transfer unit length
   b.
   • Shift direction
   c.
   • Clock frequency
   d.
   • Clock polarity and phase (CPOL and CPHA)
   e.
   • Slave select polarity
   • For a SD/MMC card, the following settings should be used:
     a.
     • Transfer unit length: 8-bits
     b.
     • Shift direction: MSB first
     c.
     • Clock frequency: 400-kHz (initially)
     d.
     • Clock polarity and phase (CPOL and CPHA): CPOL = 0, CPHA = 0
     e.
     • Slave select polarity: active low.
     • The slave select (SSEL or CS) must be configured as a GPIO output; it should not be controlled by the CPU’s SPI peripheral. The SPI port’s ChipSelEn() and ChipSelDis() functions manually enable and disable the SSEL.