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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>
This commit is contained in:
Robert Jördens 2018-11-07 14:52:03 +00:00
parent 6c00ab57c0
commit e6efe830c4
1 changed files with 34 additions and 24 deletions
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56
artiq/coredevice/ad9910.py
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@ -414,45 +414,55 @@ class AD9910:
self.cpld.io_update.pulse(1*us) self.cpld.io_update.pulse(1*us)
@kernel @kernel
def tune_sync_delay(self, sync_delay_seed=9): def tune_sync_delay(self, search_seed=15):
"""Find a stable SYNC_IN delay. """Find a stable SYNC_IN delay.
This method first locates the smallest SYNC_IN validity window at This method first locates a valid SYNC_IN delay at zero validation
minimum window size and then increases the window a bit to provide some window size (setup/hold margin) by scanning around `search_seed`. It
slack and stability. then looks for similar valid delays at successively larger validation
window sizes until none can be found. It then deacreses the validation
window a bit to provide some slack and stability and returns the
optimal values.
It starts scanning delays around `sync_delay_seed` (see the :param search_seed: Start value for valid SYNC_IN delay search.
device database arguments and :class:`AD9910`) at maximum validation Defaults to 15 (half range).
window size and decreases the window size until a valid delay is found.
:param sync_delay_seed: Start value for valid SYNC_IN delay search.
:return: Tuple of optimal delay and window size. :return: Tuple of optimal delay and window size.
""" """
dt = 14 # 1/(f_SYSCLK*75ps) taps per SYSCLK period search_span = 31
max_delay = dt # 14*75ps > 1ns # FIXME https://github.com/sinara-hw/Urukul/issues/16
max_window = dt//4 + 1 # 75ps*4 = 300ps setup and hold # should both be 2-4 once kasli sync_in jitter is identified
min_window = 1 # 1*75ps setup and hold min_window = 0
for window in range(max_window - min_window + 1): margin = 1 # 1*75ps setup and hold
window = max_window - window for window in range(16):
for in_delay in range(max_delay): next_seed = -1
# alternate search direction around seed_delay for in_delay in range(search_span - 2*window):
# alternate search direction around search_seed
if in_delay & 1: if in_delay & 1:
in_delay = -in_delay in_delay = -in_delay
in_delay = sync_delay_seed + (in_delay >> 1) in_delay = search_seed + (in_delay >> 1)
if in_delay < 0 or in_delay > 31: if in_delay < 0 or in_delay > 31:
continue continue
self.set_sync(in_delay, window) self.set_sync(in_delay, window)
self.clear_smp_err() self.clear_smp_err()
# integrate SMP_ERR statistics for a few hundred cycles # integrate SMP_ERR statistics for a few hundred cycles
# delay(10*us) delay(100*us)
err = urukul_sta_smp_err(self.cpld.sta_read()) err = urukul_sta_smp_err(self.cpld.sta_read())
delay(40*us) # slack delay(40*us) # slack
if not (err >> (self.chip_select - 4)) & 1: if not (err >> (self.chip_select - 4)) & 1:
window -= min_window # add margin next_seed = in_delay
self.set_sync(in_delay, window) break
if next_seed >= 0: # valid delay found, scan next window
search_seed = next_seed
continue
elif window > min_window:
# no valid delay found here, roll back and add margin
window = max(min_window, window - 1 - margin)
self.set_sync(search_seed, window)
self.clear_smp_err() self.clear_smp_err()
delay(40*us) # slack delay(100*us) # slack
return in_delay, window return search_seed, window
else:
break
raise ValueError("no valid window/delay") raise ValueError("no valid window/delay")
@kernel @kernel