61 lines
2.6 KiB
Python
61 lines
2.6 KiB
Python
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# Copyright 2023 XMOS LIMITED.
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# This Software is subject to the terms of the XMOS Public Licence: Version 1.
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class port_timer_pfd():
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def __init__(self, nominal_output_hz, nominal_control_rate_hz, ppm_range=1000):
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self.output_count_last = 0.0 # Integer value of last output_clock_count
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self.first_loop = True
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self.ppm_range = ppm_range
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self.expected_output_clock_count_inc = nominal_output_hz / nominal_control_rate_hz
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def get_error(self, output_clock_count_float, period_fraction=1.0):
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"""
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Calculate frequency error from the port output_count taken at the ref clock time.
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Note it uses a floating point input clock count to make simulation easier. This
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handles fractional counts and carries them properly.
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If the time of sampling the output_count is not precisely 1.0 x the ref clock time,
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you may pass a fraction to allow for a proportional value using period_fraction. This is optional.
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"""
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output_count_int = int(output_clock_count_float) # round down to nearest int to match hardware
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output_count_inc = output_count_int - self.output_count_last
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output_count_inc = output_count_inc / period_fraction
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expected_output_clock_count = self.output_count_last + self.expected_output_clock_count_inc
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error = output_count_inc - int(self.expected_output_clock_count_inc)
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# Apply out of range detection so that the controller ignores startup or missed control loops (as per C)
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if abs(error) > (self.ppm_range / 1e6) * self.expected_output_clock_count_inc:
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# print("PFD FIRST LOOP", abs(error), (self.ppm_range / 10e6) * self.expected_output_clock_count_inc)
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self.first_loop = True
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else:
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self.first_loop = False
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self.output_count_last = output_count_int
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return error, self.first_loop
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if __name__ == '__main__':
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"""
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This module is not intended to be run directly. This is here for internal testing only.
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"""
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nominal_output_hz = 12288000
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nominal_control_rate_hz = 93.75
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expected_output_clock_inc = nominal_output_hz / nominal_control_rate_hz
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pfd = port_timer_pfd(nominal_output_hz, nominal_control_rate_hz)
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output_clock_count_float = 0.0
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for output_hz in range(nominal_output_hz - 1000, nominal_output_hz + 1000, 10):
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output_clock_count_float += output_hz / nominal_output_hz * expected_output_clock_inc
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error = pfd.get_error(output_clock_count_float)
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print(f"actual output Hz: {output_hz} output_clock_count: {output_clock_count_float} error: {error}")
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