Simple GPS RF front-end simulator based on STM32

This device is based on STM32F103C8T6 (blue pill).
It generates serial data using SPI (CLK + MOSI), and emulating 1-bit ADC of GPS RF front-end.
Software is emulating receiving of one GPS satellite, which is sending constant navigation data (subframe 1).

CLK frequency is 16 MHz, data IF frequency is 4 MHz, which is close to parameters of MAX2769.
PA5 is CLK
PA7 is MOSI