Using VHDL, I implements state-machine using a simple "switch case" on an '''integer'''. and before break I just change (increment...) this integer variable value, changing line of "switch case" this way.
This "switch case" is encalupsed on a "if do/done do/done do/done" instruction. "do" being a boolean from MASTER, and "done" being a boolean from SLAVE. Each MASTER against SLAVE component has a "do" (input if SLAVE component, output if MASTER component) and a "done" (input if MASTER component, output if SLAVE component) wire.
That's all. Like this you can run several sequential instructions, like reading and interpreting severals FAT32 variables using a SPI slaved component solving "read one byte at this address" turned into instruction writen under a really low-level SDCARD protocol language.
Theses state-machines does use led debug : an '''integer''' contains the state of state machine, and this '''integer''' is displayed on 8 leds so you know where you are, it's for that I add several crash states in order to understand why and where component does crash. In MiST-board, this is displayed on the five 7-segment I added in OSD, I add also an input in order to select one or another state machine.