===== State machine =====
Both component components of Bootloader, it is to say SPI_MASTER and SDRAM_FAT32_LOADER components, does use several state-machines, one state-machine per process, each process communicating with another one using "MASTER/SLAVE" : the master state-machine does ask a slave to do something, and slave does notify master when its task is finished.
Using VHDL, I implements state-machine using a simple "switch case" on an '''integer'''. and before break I just change this integer variable value, changing line of "switch case" this way.