Finite State Machine Generator

This notebook will show how to use the Finite State Machine (FSM) Generator to generate a state machine. The FSM we will build is a Gray code counter. The counter has three state bits and can count up or down through eight states. The counter outputs are Gray coded, meaning that there is only a single-bit transition between the output vector of any state and its next states.

Step 1: Download the `logictools` overlay



In [1]:

    
from pynq.overlays.logictools import LogicToolsOverlay

logictools_olay = LogicToolsOverlay('logictools.bit')

Step 2: Specify the FSM



In [2]:

    
fsm_spec = {'inputs': [('reset','D0'), ('direction','D1')],
            'outputs': [('bit2','D3'), ('bit1','D4'), ('bit0','D5')],
            'states': ['S0', 'S1', 'S2', 'S3', 'S4', 'S5', 'S6', 'S7'],
            'transitions': [['01', 'S0', 'S1', '000'],
                            ['00', 'S0', 'S7', '000'],
                            ['01', 'S1', 'S2', '001'],
                            ['00', 'S1', 'S0', '001'],
                            ['01', 'S2', 'S3', '011'],
                            ['00', 'S2', 'S1', '011'],
                            ['01', 'S3', 'S4', '010'],
                            ['00', 'S3', 'S2', '010'],
                            ['01', 'S4', 'S5', '110'],
                            ['00', 'S4', 'S3', '110'],
                            ['01', 'S5', 'S6', '111'],
                            ['00', 'S5', 'S4', '111'],
                            ['01', 'S6', 'S7', '101'],
                            ['00', 'S6', 'S5', '101'],
                            ['01', 'S7', 'S0', '100'],
                            ['00', 'S7', 'S6', '100'],                            
                            ['1-', '*',  'S0', '']]}

Notes on the FSM specification format

Step 3: Instantiate the FSM generator object



In [3]:

    
fsm_generator = logictools_olay.fsm_generator

Setup to use trace analyzer
In this notebook trace analyzer is used to check if the inputs and outputs of the FSM.

Users can choose whether to use the trace analyzer by calling the trace() method.



In [4]:

    
fsm_generator.trace()

Step 5: Setup the FSM generator

The FSM generator will work at the default frequency of 10MHz. This can be modified using a frequency argument in the setup() method.



In [5]:

    
fsm_generator.setup(fsm_spec)

Display the FSM state diagram
This method should only be called after the generator has been properly set up.



In [6]:

    
fsm_generator.show_state_diagram()

Set up the FSM inputs on the PYNQ board

Check that the reset and direction inputs are correctly wired on the PYNQ board, as shown below:
- Connect D0 to GND
- Connect D1 to 3.3V

Notes:

The 3-bit Gray code counter is an up-down, wrap-around counter that will count from states 000 to 100 in either ascending or descending order

The reset input is connected to pin D0 of the Arduino connector
- Connect the reset input to GND for normal operation
- When the reset input is set to logic 1 (3.3V), the counter resets to state 000

The direction input is connected to pin D1 of the Arduino connector
- When the direction is set to logic 0, the counter counts down
- Conversely, when the direction input is set to logic 1, the counter counts up

Step 6: Run and display waveform

The run() method will execute all the samples, show_waveform() method is used to display the waveforms



In [7]:

    
fsm_generator.run()
fsm_generator.show_waveform()

Verify the trace output against the expected Gray code count sequence

State	FSM output bits: bit2, bit1, bit0
s0	000
s1	001
s2	011
s3	010
s4	110
s5	111
s6	101
s7	100

Step 7: Stop the FSM generator

Calling stop() will clear the logic values on output pins; however, the waveform will be recorded locally in the FSM instance.



In [8]:

    
fsm_generator.stop()