  BESIII is a multipurpose spectrometer optimized for physics in the tau-charm
energy region. Both detector and accelerator are undergoing an upgrade program,
that will allow BESIII to run until 2029. A major upgrade is the replacement of
the inner drift chamber with a new detector based on Cylindrical Gas Electron
Multipliers to improve both the secondary vertex reconstruction and the
radiation tolerance. The CGEM-IT will be composed of three coaxial layers of
cylindrical triple GEMs, operating in an Ar$\,$+$\,$iC$_4$H$_{10}$ (90:10) gas
mixture with field and gain optimized to maximize the spatial resolution. The
new detector is readout with innovative TIGER electronics produced in 110$\,$nm
CMOS technology. The front end is a custom designed 64$\,$channel ASIC
featuring a fully digital output and operated in trigger-less mode. It can
provide analog charge and time measurements with a TDC time resolution better
than 100$\,$ps, that will allow to operate in $\mu$TPC mode. Before the
installation inside BESIII, foreseen in 2021, a long standalone data taking is
ongoing at the Institute of High Energy Physics in Beijing; currently, the
first two cylindrical chambers are available for the test, and are used to
complete the integration between the detector and the electronics and to assess
the required performance. In this proceeding a description of the CGEM-IT
project, the TIGER features and performance, and the results of the analysis of
first cosmic ray data taking will be presented. Focus will be given on the
strip analysis, from which it is possible to measure the basic properties of
the detector, and the cluster analysis. The first preliminary results on
efficiency and spatial resolution will be also presented.
