esp8266-sparkfun-thing/include/board.h

Board specific definitions for SparkFun ESP8266 Thing boards.

LED0_PIN

GPIO5 is used as LED Pin. 

1
GPIO5
LED0_ACTIVE

LED is high active. 

1
(1)
SPI0_CS0_GPIO

GPIO15 is not available on SparkFun Thing Dev. 

1
GPIO16

Therefore another GPIO is define as default CS signal for HSPI interface spi.h::SPI_DEV.HSPI / spi.h::SPI_DEV CS default pin, only used when cs parameter in spi_acquire is GPIO_UNDEF