#!/usr/bin/env python
# coding: utf-8

# # Example: Hysteresis with simple FSM

# In[1]:


from cyhdl import *


# We create a little state machine with three states as shown below. Note: Upon reset, the `@always_seq` logic implicitely resets `state` variable to `NEUTRAL` state.

# In[2]:


@block
def hysteresis(
    clk : ClkSignal,
    reset : ResetSignal,
    a   : Signal,
    q0  : Signal.Output,
    q1  : Signal.Output,
    *,
    LOWER : int = 0,
    UPPER : int = 255
):
    t_state = enum('NEUTRAL', 'OVER', 'UNDER', name='t_state')
    
    state = Signal(t_state.NEUTRAL)
    
    @always_seq(clk.posedge, reset)
    def worker():           
        if state == t_state.OVER:
            if a < LOWER:
                state.next = t_state.UNDER    
        elif state == t_state.UNDER:
            if a > UPPER:
                state.next = t_state.OVER
        else:
            if a < LOWER:
                state.next = t_state.UNDER
            elif a > UPPER:
                state.next = t_state.OVER
                
    @always_comb
    def assign():
        if state == t_state.OVER:
            q0.next = False
            q1.next = True
        elif state == t_state.UNDER:
            q0.next = True
            q1.next = False
        else:
            q0.next = False
            q1.next = False

    return instances()


# Then we create a test bench with a bit of ramping stimulus:

# In[3]:


from myirl.test.common_test import run_ghdl, gen_osc

@block
def testbench_hyst(SIZE = 6):
    clk = ClkSignal()
    rst = ResetSignal(0, 1, isasync = False)
    val = Signal(intbv()[SIZE:])
    lo, hi = [ Signal(bool()) for i in range(2) ]
    
    inst = hysteresis(clk = clk, reset = rst, a = val, q0 = lo, q1 = hi,
                     LOWER = 4, UPPER = 16)

    cg = gen_osc(clk, CYCLE = 1)
    
    N = 2 ** SIZE
    
    @instance
    def stim():
        val.next = 8
        rst.next = True
        yield delay(10)
        rst.next = False
        for i in range(8, N):
            val.next = i
            yield delay(2)

        for i in range(N-1, -1, -1):
            val.next = i
            yield delay(2)

        val.next = 8
        rst.next = True
        yield delay(10)
        rst.next = False
            
        for i in range(8, -1, -1):
            val.next = i
            yield delay(5)
            
        for i in range(0, N):
            val.next = i
            yield delay(2)
            
    return instances()


# In[4]:


def test():
    tb = testbench_hyst()
    files = tb.elab(targets.VHDL, elab_all = True)
    run_ghdl(files, tb, vcdfile='hyst.vcd', debug=True)
    return files


# In[5]:


f = test()


# As a result, the wave trace (download [hyst.vcd](hyst.vcd)) displays as follows in GTKwave:

# ![Wave trace](wave.png)

# In[6]:


get_ipython().system('cat {f[1]}')


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