[time-nuts] Time-Interval counter

[hans-georg at lehnard.de]

Hi all, 

I am working on a time interval counter which basically consists of 4
components :
input (LTC9657), divider by 100 (XCR3064), time-to-digital converter
(AS6501; 10ps RMS) and a microcontroller STM32H743-Nucleo Board.
Because of the SPI speed max 100k samples/s are possible. The STM32H7
can store 32000 samples with 1ps resolution in RAM ~ 0.1s. 

The AS6501 can also sample 10MHz directly via LVDS (DDR) outputs, but
this requires an FPGA. This will be my next project ;-) 

One sample takes 5µs for acquisition so I have 5µs left for
calculations. STM32 runs at 480MHz. 
Is there a way (on the fly) to combine e.g. 1000 samples to one value
(MDEV or TDEV) ?. 

I have tested a HP10811 as input and LTC9657-4 (direct and inverted
output). Direct output goes to AS6501 REF input and inverted goes to the
divider. Raw data and ADEV,MDEV,TDEV from a test with HP10811-60111
attached. 

Statistics for 32k samples 

p1
MAX: 10000244 ps
MIN: 9999771 ps
MAX - MIN: 473 ps
AVG: 9999999 ps 

p2
MAX: 10000206 ps
MIN: 9999797 ps
MAX - MIN: 409 ps
AVG: 9999999 ps 

p3
MAX: 10000226 ps
MIN: 9999780 ps
MAX - MIN: 446 ps
AVG: 9999999 ps 

p4
MAX: 10000229 ps
MIN: 9999775 ps
MAX - MIN: 454 ps
AVG: 10000000 ps 

p5
MAX: 10000220 ps
MIN: 9999772 ps
MAX - MIN: 448 ps
AVG: 9999999 ps
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