  We discuss how a level-1 trigger, about 8 us after a hadron-hadron collision,
can be derived from the Transition Radiation Detector (TRD) in A Large Ion
Collider Experiment (ALICE) at the LHC. Chamber-wise track segments from fast
on-detector reconstruction are read out with position, angle and electron
likelihood. In the Global Tracking Unit up to 6 tracklets from a particle
traversing the detector layers are matched and used for the reconstruction of
transverse momentum and electron identification. Such tracks form the basis for
versatile and flexible trigger conditions, e.g. single high-pt hadron, single
high-pt electron, di-electron (J/Psi, Upsilon) and at least n close high-pt
tracks (jet).
  The need for low-latency on-line reconstruction poses challenges on the
detector operation. The calibration for gain (pad-by-pad) and drift velocity
must be applied already in the front-end electronics. Due to changes in
pressure and gas composition an on-line monitoring and feedback loop for these
parameters is required. First experiences on the performance were gathered from
triggering in cosmic and pp runs.
