forked from M-Labs/artiq
ad9910: rewire sync delay tuning
* search from wide window end * decouple margins and minimum window size * add note about kasli jitter Signed-off-by: Robert Jördens <rj@quartiq.de>
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@ -414,45 +414,55 @@ class AD9910:
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self.cpld.io_update.pulse(1*us)
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@kernel
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def tune_sync_delay(self, sync_delay_seed=9):
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def tune_sync_delay(self, search_seed=15):
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"""Find a stable SYNC_IN delay.
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This method first locates the smallest SYNC_IN validity window at
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minimum window size and then increases the window a bit to provide some
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slack and stability.
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This method first locates a valid SYNC_IN delay at zero validation
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window size (setup/hold margin) by scanning around `search_seed`. It
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then looks for similar valid delays at successively larger validation
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window sizes until none can be found. It then deacreses the validation
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window a bit to provide some slack and stability and returns the
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optimal values.
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It starts scanning delays around `sync_delay_seed` (see the
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device database arguments and :class:`AD9910`) at maximum validation
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window size and decreases the window size until a valid delay is found.
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:param sync_delay_seed: Start value for valid SYNC_IN delay search.
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:param search_seed: Start value for valid SYNC_IN delay search.
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Defaults to 15 (half range).
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:return: Tuple of optimal delay and window size.
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"""
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dt = 14 # 1/(f_SYSCLK*75ps) taps per SYSCLK period
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max_delay = dt # 14*75ps > 1ns
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max_window = dt//4 + 1 # 75ps*4 = 300ps setup and hold
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min_window = 1 # 1*75ps setup and hold
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for window in range(max_window - min_window + 1):
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window = max_window - window
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for in_delay in range(max_delay):
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# alternate search direction around seed_delay
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search_span = 31
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# FIXME https://github.com/sinara-hw/Urukul/issues/16
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# should both be 2-4 once kasli sync_in jitter is identified
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min_window = 0
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margin = 1 # 1*75ps setup and hold
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for window in range(16):
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next_seed = -1
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for in_delay in range(search_span - 2*window):
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# alternate search direction around search_seed
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if in_delay & 1:
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in_delay = -in_delay
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in_delay = sync_delay_seed + (in_delay >> 1)
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in_delay = search_seed + (in_delay >> 1)
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if in_delay < 0 or in_delay > 31:
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continue
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self.set_sync(in_delay, window)
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self.clear_smp_err()
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# integrate SMP_ERR statistics for a few hundred cycles
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# delay(10*us)
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delay(100*us)
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err = urukul_sta_smp_err(self.cpld.sta_read())
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delay(40*us) # slack
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if not (err >> (self.chip_select - 4)) & 1:
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window -= min_window # add margin
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self.set_sync(in_delay, window)
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self.clear_smp_err()
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delay(40*us) # slack
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return in_delay, window
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next_seed = in_delay
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break
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if next_seed >= 0: # valid delay found, scan next window
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search_seed = next_seed
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continue
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elif window > min_window:
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# no valid delay found here, roll back and add margin
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window = max(min_window, window - 1 - margin)
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self.set_sync(search_seed, window)
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self.clear_smp_err()
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delay(100*us) # slack
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return search_seed, window
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else:
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break
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raise ValueError("no valid window/delay")
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@kernel
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