CPU_BOOLEAN FSDev_BSP_SPI_Open (FS_QTY unit_nbr);

File	Called from	Code enabled by
`fs_dev_<dev_name>_bsp.c`	Device driver	N/A

Open (initialize) hardware for SPI.

unit_nbr

Unit number of device.

DEF_OK, if interface was opened.

DEF_FAIL, otherwise.

This function will be called every time the device is opened.
Several aspects of SPI communication may need to be configured, including:
- Transfer unit length
- Shift direction
- Clock frequency
- Clock polarity and phase (CPOL and CPHA)
- Slave select polarity
For a SD/MMC card, the following settings should be used:
- Transfer unit length: 8-bits
- Shift direction: MSB first
- Clock frequency: 400-kHz (initially)
- Clock polarity and phase (CPOL and CPHA): CPOL = 0, CPHA = 0
- 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.

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