Not really for factory, but obviously running a calibration on each board is quite time intensive.
I was wondering whether we can use the 'QTR_Clk' output to sense the XTAL/TXCO frequency once and apply a calibration value for each of the possible FPSs. I have a Sync-IO which can use work-clock as a reference source, and then it's SMPTE output is timed according to that. I also have a studio quality work-clock, but it's not perfect. If this idea is 'do-able' then perhaps a GPSDO would be better.
At present I don't have a good way of measuring frequency. I can use my Saleae at 500MS/s and then manually apply the measurement tool.
"48KHz" reference, measured by Saleae @ 500MS/s
ΔT 10.01152786853358 s
Nfalling 480545
Nrising 480545
fmin 47993.856786325036 Hz
fmax 48003.072200455026 Hz
fmean 47999.16338835829 Hz
Tstd 7.181951195629003e-10 s
QTR_Clock - is either 1x or 4x fps rate
25fps, before calibration
WaveShare with XTAL (not replaced!!)
ΔT 9.991685704 s
Nfalling 250
Nrising 250
fmin 25.006879392520876 Hz
fmax 25.006886896652713 Hz
fmean 25.006882556912693 Hz
Tstd 3.4454835055419842e-9 s
25fps, after calibration
ΔT 10.049693698 s
Nfalling 252
Nrising 252
fmin 24.99958500688894 Hz
fmax 24.999630005476856 Hz
fmean 24.999619303606043 Hz
Tstd 1.6651627135330096e-8 s
ΔT 10.071959868743203 s
Nfalling 483445
Nrising 483446
fmin 47993.85678285529 Hz
fmax 48003.072200455026 Hz
fmean 47999.1425788096 Hz
Tstd 7.095777089464976e-10 s
Working with fact that reference is not perfect:
48000/47999.1425788096 = 1.0000178632605570444009661954602
24.999619303606043 * 1.0000178632605570444009661954602 = 25.000065878319490231643040344738
Not really for factory, but obviously running a calibration on each board is quite time intensive.
I was wondering whether we can use the 'QTR_Clk' output to sense the XTAL/TXCO frequency once and apply a calibration value for each of the possible FPSs. I have a Sync-IO which can use work-clock as a reference source, and then it's SMPTE output is timed according to that. I also have a studio quality work-clock, but it's not perfect. If this idea is 'do-able' then perhaps a GPSDO would be better.
At present I don't have a good way of measuring frequency. I can use my Saleae at 500MS/s and then manually apply the measurement tool.
"48KHz" reference, measured by Saleae @ 500MS/s
QTR_Clock - is either 1x or 4x fps rate
25fps, before calibration
WaveShare with XTAL (not replaced!!)
25fps, after calibration
Working with fact that reference is not perfect:
48000/47999.1425788096 = 1.0000178632605570444009661954602
24.999619303606043 * 1.0000178632605570444009661954602 = 25.000065878319490231643040344738