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ad9910: rewire sync delay tuning

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* 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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58
artiq/coredevice/ad9910.py
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@ -414,45 +414,55 @@ class AD9910:
self.cpld.io_update.pulse(1*us)
@kernel
def tune_sync_delay(self, sync_delay_seed=9):
def tune_sync_delay(self, search_seed=15):
"""Find a stable SYNC_IN delay.
This method first locates the smallest SYNC_IN validity window at
minimum window size and then increases the window a bit to provide some
slack and stability.
This method first locates a valid SYNC_IN delay at zero validation
window size (setup/hold margin) by scanning around `search_seed`. It
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
device database arguments and :class:`AD9910`) at maximum validation
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.
:param search_seed: Start value for valid SYNC_IN delay search.
Defaults to 15 (half range).
:return: Tuple of optimal delay and window size.
"""
dt = 14 # 1/(f_SYSCLK*75ps) taps per SYSCLK period
max_delay = dt # 14*75ps > 1ns
max_window = dt//4 + 1 # 75ps*4 = 300ps setup and hold
min_window = 1 # 1*75ps setup and hold
for window in range(max_window - min_window + 1):
window = max_window - window
for in_delay in range(max_delay):
# alternate search direction around seed_delay
search_span = 31
# FIXME https://github.com/sinara-hw/Urukul/issues/16
# should both be 2-4 once kasli sync_in jitter is identified
min_window = 0
margin = 1 # 1*75ps setup and hold
for window in range(16):
next_seed = -1
for in_delay in range(search_span - 2*window):
# alternate search direction around search_seed
if in_delay & 1:
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:
continue
self.set_sync(in_delay, window)
self.clear_smp_err()
# integrate SMP_ERR statistics for a few hundred cycles
# delay(10*us)
delay(100*us)
err = urukul_sta_smp_err(self.cpld.sta_read())
delay(40*us) # slack
if not (err >> (self.chip_select - 4)) & 1:
window -= min_window # add margin
self.set_sync(in_delay, window)
self.clear_smp_err()
delay(40*us) # slack
return in_delay, window
next_seed = in_delay
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()
delay(100*us) # slack
return search_seed, window
else:
break
raise ValueError("no valid window/delay")
@kernel