Analog output and TTL counter phase match

Hello,

I want to generate two analog output signals (2100Hz sine wave) and TTL signal (from ctr2).

When I set the frequencies of these signals to be the same, I found that the analog output and the TTL signal were misaligned on the oscilloscope. What is the reason?

The code i have question can found in initialize.twoD_lissajous_configure.twoD_lissajous_run function

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