I am looking for a solution to do faster data acquisition than with my current ATXmega256A3BU setup (32MHz).
With the Xmega and using Bascom IDE that is quite a simple task.
But with the Teensys I did not find a solution.

It's kind of boxcar integrator with the purpose of averaging the ADC-readings over a couple of externally triggered time-sweeps from a periodic master signal that is fed to the CPU's comparator input.
Signal-input (extremely noisy) is to an ADC, the master signal (500Hz sinus) is fed to the internal comparator and upon each trigger event the DMA transfers the ADC readings to RAM.
Then the RAM is copied to an array and upon the next trigger the new results are added to the array. This in effect acts a a low-pass filter.
After about 64 of those triggered cycles the contents of the array is evaluated (and displayed on a TFT display).

To start with I tried codes like from this thread (#20 or #17) but they are not giving any output to the serial monitor.

On the trigger issue I did not find promising suggestions so far.

Could somebody kindly suggest how to achieve that (i.e. external triggered ADC_DMA transfer) with a Teensy (have 3.5 and 4 at present)?