from vcd import VCDWriter
import sys
def generate_vcd(num_cycles=20):
with VCDWriter(sys.stdout, timescale='1 ns', date='today') as writer:
# Register variables
clk = writer.register_var('top', 'clk', 'reg', size=1)
ff = []
for i in range(5):
ff.append(writer.register_var('top', f'ff{i}', 'reg', size=1))
# Initial state
writer.change(clk, 0, 0) # Clock starts at 0
writer.change(ff[0], 0, 1) # First FF has the pulse
for i in range(1, 5):
writer.change(ff[i], 0, 0)
# Simulate for specified number of cycles
ff_state = [1, 0, 0, 0, 0] # Current state of flip-flops
for t in range(1, num_cycles * 2):
# Toggle clock every time unit
clock_value = t % 2
writer.change(clk, t, clock_value)
# On rising edge (clock transitions from 0 to 1)
if clock_value == 1:
# Shift the FF values
ff_state = [ff_state[-1]] + ff_state[:-1]
# Update all FFs
for i in range(5):
writer.change(ff[i], t, ff_state[i])
if __name__ == '__main__':
generate_vcd()