GNAM: a low level monitoring program for the ATLAS experiment

During the last years many test-beam sessions were carried out on each ATLAS sub detector in order to assess the standalone performances. During these sessions, different monitoring programs were developed to ease the setup of correct running conditions and the assessment of data quality. The experience acquired in developing these programs is now converging into a more general monitoring program, which aims to be exploitable by various sub detector groups. The requirements that drove the design of this program are discussed in detail in this paper. The outcome is a highly modular program which uses a finite state machine core to implement the synchronization and which exploits the ROOT tree for transient data storage. The first version of this monitoring program was used for the 2004 ATLAS combined test beam. After a description of the program architecture, the first results and performances obtained at the test beam will be discussed.