btashton opened a new pull request #1788:
URL: https://github.com/apache/incubator-nuttx/pull/1788


   ## Summary
   This adds a new GPIO functional mode GPIO_DISABLED where
   pins for hardware like the SPI controller can be defined
   but not connected to physical pin.
   
   This also implements this feature in the nRF SPIM driver
   and was tested leaving the MISO pin disconnected.
   
   ## Impact
   Right now is it really hard to not bring out all pins for a hardware block 
even if they are not used.  In my use case I need to use the SPI driver to 
control and LED driver, but it is used only as a single IO pin.  I still have 
to bring out the CLK (SPIM docs clarify this) but I no longer have to waste a 
physical pin.
   
   ## Testing
   Was able to drive the LED controller with out SCK and MOSI connected to pins.
   
   ```
   #define BOARD_SPI1_SCK_PIN (GPIO_OUTPUT | GPIO_VALUE_ZERO | GPIO_PORT0 | 
GPIO_PIN(16))
   #define BOARD_SPI1_MOSI_PIN (GPIO_OUTPUT | GPIO_VALUE_ZERO | GPIO_PORT0 | 
GPIO_PIN(7))
   #define BOARD_SPI1_MISO_PIN (GPIO_DISABLED)
   ```
   


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