Calculation of secondary particles produced by the interaction of cosmic rays
with the nuclei of Earth's atmosphere pose important requirements to particle
production models. Here we summarize the important features of hadronic
simulations, stressing the importance of the so called ``microscopic''
approach, making explicit reference to the case of the FLUKA code. Some
benchmarks are also presented.Comment: 10 pages, 4 figures. Extended version of report given at the IInd
Workshop on Matter and anti-Matter, Trento, Oct. 200