  Drifting pulsation structures (DPSs) are important radio fine structures
usually observed at the beginning of eruptive solar flares. It has been
suggested that DPSs carry important information on the energy release processes
in solar flares. We study DPS observed in an X8.2-class flare on 2017 September
10 in the context of spatial and spectral diagnostics provided by microwave,
EUV, and X-ray observations. We describe DPS and its sub-structures that were
observed for the first time. We use a new wavelet technique to reveal
characteristic periods in DPS and their frequency bands. Comparing the periods
of pulsations found in this DPS with those in previous DPSs we found new very
short periods in the 0.09-0.15 s range. We present EOVSA images and spectra of
microwave sources observed during the DPS. This DPS at its very beginning has
pulsations in two frequency bands (1000-1300 MHz and 1600--1800 MHz) which are
interconnected by fast drifting bursts. We show that these double-band
pulsations started just at the moment when the ejected filament splits apart in
a tearing motion at the location where a signature of the flare current
sheetlater appeared. Using the standard flare model and previous observations
of DPSs, we interpret these double-band pulsations as a radio signature of
superthermal electrons trapped in the rising magnetic rope and flare arcade at
the moment when the flare magnetic reconnection starts. The results are
discussed in a scenario with the plasmoid in the rising magnetic rope.
