How to program a pressure sensor using the SPI Bus

I am using the STM32 Microcontroller (as part of the LoRa node MB1296D). I want to connect a pressure sensor (MS5803) to the LoRa node and program the sensor via the SPI Bus. Basically, this is all very new to me, which is why I looked up an example code

I am trying to understand this code and a couple of questions have come up:

the macros that are defined in the very beginning, what exactly is their purpose, and are the hexadecimal numbers inherent to the used microcontroller? - If I was to write a code from scratch, I figured I would start by defining macros for the GPIO Pins corresponding to SPI_SCK, SPI_MISO and SPI_MOSI
the function unsigned long cmd_adc(char cmd) contains a switch command, which I have absolutely no clue as on what is does. I mean it looks to me as if I am trying to set the resolution of the ADC, but how do I know the corresponding delay and why does the switch command contain the 0x0f ?

So. If you could find some time to give me a useful answer, that'd be great! Also, if you know any good readings with special focus on this topic, please tell me! I am trying to tackle this problem with little time available.

Solution

Your questions are basic C programming questions and are not really specific to this pressure sensor or example.

The macros are defined with hexadecimal numbers to make it clear that the values represent bit fields. It's very easy (and second nature for embedded software developers) to convert hexadecimal to binary. Read the register descriptions in the sensor's datasheet. The bits set in the hexadecimal values will correspond to meaningful bits in the sensor's register description.

switch (cmd & 0x0f) performs a bitwise AND of the cmd with 0x0f. The hexadecimal value 0x0f has the four least significant bits set. So the code is ignoring (i.e., masking off or zeroing out) the four most significant bits of cmd and considering only the four least significant bits of the cmd value.