gowin.py

        def _calculate_params(self, platform):
            key = (platform.family, platform.speed)
            try:
                info = self.PLL_INFO[key]
            except KeyError:
                raise NotImplementedError('PLL not implemented for {!r}'.format(key))

            fclkin = self.in_period.megahertz
            params = None
            diff = None

            names = ['IDIV_SEL', 'pfd', 'FBDIV_SEL', 'clkout', 'ODIV_SEL', 'vco', 'DYN_SDIV_SEL', 'clkoutd']
            valids = (
                {n: locals()[n] for n in names}

                for IDIV_SEL in range(64)
                if info['pfd'][0] <= (pfd := fclkin / (IDIV_SEL + 1)) <= info['pfd'][1]

                for FBDIV_SEL in range(64)
                if info['clkout'][0] < (clkout := pfd * (FBDIV_SEL + 1)) < info['clkout'][1]

                for ODIV_SEL in range(2, 130, 2)
                if info['vco'][0] < (vco := clkout * ODIV_SEL) < info['vco'][1]

                # 0 stands in for "use clkout not clkoutd"
                for DYN_SDIV_SEL in range(0, 130, 2)
                if (clkoutd := clkout / max(DYN_SDIV_SEL, 1)) or True
            )

            for v in valids:
                new_params = info.copy()
                new_params.update(v)
                new_params.update({
                    'output': v['clkoutd'],
                    'output_signal': 'CLKOUTD',
                    'fclkin': fclkin,
                    'FCLKIN': '{:.6f}'.format(fclkin),
                })

                if v['DYN_SDIV_SEL'] == 0:
                    new_params.update({
                        'output': v['clkout'],
                        'output_signal': 'CLKOUT',
                    })

                    del new_params['DYN_SDIV_SEL']
                    del new_params['clkoutd']

                new_diff = abs((new_params['output'] / self.out_period.megahertz) - 1)
                if params is None or diff > new_diff:
                    params = new_params
                    diff = new_diff

            ppm = diff * 1e6
            if ppm > self.MAX_PPM:
                raise RuntimeError('PLL settings not found: wanted {:.6f}, best is {:.6f} ({:.0f} ppm)'.format(self.out_period.megahertz, params['output'], ppm))

            self._params = params
            self.out_period = am.Period(MHz=params['output'])