| """ |
| A model of the MASH mdulator. |
| """ |
| |
| class mash_mod_model(): |
| |
| def __init__(self, modulus_width, order): |
| """ |
| Instatiate the model object |
| """ |
| |
| # store the modulator parameters |
| self.modulus_width = modulus_width |
| self.order = order |
| |
| # create internal state variables |
| self.accum_delay = [0.0]*order |
| self.accum_out = [0.0]*order |
| self.accum_carry = [0.0]*order |
| self.sum_delay = [0.0]*(order-1) |
| |
| # calculate the delay in processing |
| # self.delay = 4*(self.order-1)+1 |
| self.delay = 4*(self.order-1) |
| self.delay_line = [0.0] * self.delay |
| |
| |
| def reset(self): |
| """ |
| Reset the internal state of the modulator |
| """ |
| |
| # reset internal state variables |
| self.accum_delay = [0.0]*self.order |
| self.accum_out = [0.0]*self.order |
| self.accum_carry = [0.0]*self.order |
| self.sum_delay = [0.0]*(self.order-1) |
| self.delay_line = [0] * self.delay |
| |
| |
| def update(self, input_data): |
| """ |
| Update the state of the modulator with new data |
| """ |
| |
| # convert fractional number to unsigned integer |
| input_data_int = int(input_data * 2**self.modulus_width) |
| |
| # loop through the different stages in the modulator |
| for i in range(self.order): |
| |
| # calculate accumulator outputs |
| if i == 0: |
| self.accum_out[i] = input_data_int + self.accum_delay[i] |
| else: |
| self.accum_out[i] = self.accum_out[i-1] + self.accum_delay[i] |
| |
| # treat as fixed point numbers |
| self.accum_carry[i] = int(self.accum_out[i]/(2**self.modulus_width)) |
| self.accum_out[i] = int((self.accum_out[i])%(2**self.modulus_width)) |
| self.accum_delay[i] = self.accum_out[i] |
| |
| # tally up carries |
| mash_output = self.accum_carry[-1] |
| for i in range(self.order-2, -1, -1): |
| temp_mash_output = mash_output |
| mash_output += self.accum_carry[i] - self.sum_delay[i] |
| self.sum_delay[i] = temp_mash_output |
| |
| # ensure the output wraps around |
| if mash_output == 4: |
| mash_output = -4 |
| |
| # delay to track pipelining |
| output_data = self.delay_line[-1] |
| self.delay_line = [mash_output] + self.delay_line[:-1] |
| |
| return output_data |
