| """ |
| A model of the LFSR quasi-random number generator. |
| """ |
| |
| class lfsr_fib_model(): |
| |
| def __init__(self, polynomial_length=8, initial_fill=1, taps=0x2D): |
| """ |
| Instatiate the model object |
| """ |
| |
| # store the modulator parameters |
| self.polynomial_length = polynomial_length |
| self.initial_fill = [int(digit) for digit in format(initial_fill, '#0'+str(polynomial_length+2)+'b')[2:]][::-1] |
| self.taps = [int(digit) for digit in format(taps, '#0'+str(polynomial_length+2)+'b')[2:]][::-1] |
| |
| # create internal state variables |
| self.reset() |
| |
| |
| def reset(self): |
| """ |
| Reset the internal state of the modulator |
| """ |
| |
| # reset internal state variables |
| self.shift_register = self.initial_fill |
| |
| |
| def update(self, input_data): |
| """ |
| Update the state of the LFSR with new data |
| """ |
| |
| previous_out = self.shift_register[0] |
| |
| if input_data["ce"]: |
| |
| # XOR the selected tap points |
| xored = self.shift_register[0] & self.taps[0] |
| for i in range(1, self.polynomial_length-1): |
| xored ^= self.shift_register[i] & self.taps[i] |
| |
| # update the shift register |
| self.shift_register = self.shift_register[1:] + [xored ^ input_data["in"]] |
| |
| return previous_out |
