SPI enlightenment

I'm puzzled by how the SPI library knows which pin is used for ss, pin 10 is predefined in pins_arduino.h, in the barometric pressure sensor example it just calls SPI.begin() and then set the designated pin to output, pinMode(chipSelectPin, OUTPUT); and everything seems to work, I soft of expect to see something like this SPI spi_device(SS) ; //constructor for different SPI devcies attached to the bus


It is built into the hardware of the Atmega chip so there is no need / no way to define it in software.