TlmChanImplCfg.hpp

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#ifndef TLMCHANIMPLCFG_HPP_
#define TLMCHANIMPLCFG_HPP_
 
// Anonymous namespace for configuration parameters
 
 
// The parameters below provide for tuning of the hash function used to
// write and read entries in the database. The has function is very simple;
// It first takes the telemetry ID and does a modulo computation with
// TLMCHAN_HASH_MOD_VALUE. It then does a second modulo with the number
// of slots to make sure the value lands in the provided slots.
// The values can be experimented with to try and balance the number
// of slots versus the number of buckets.
// To test the set of telemetry ID in the system to see if the hash is
// balanced, do the following:
//  1) From the deployment directory (e.g Ref), do a full build then type:
//      "make comp_report_gen"
//     This will generate a list in "<deployment dir>/ComponentReport.txt"
//     with all the telemetry IDs in the deployment.
//  2) Cut and paste the ID list to the array declared in the TlmChan unit test
//     file TelemChanImplTester.cpp in the runMultiChannel() method.
//  3) Run the unit test ("make ut run_ut")
//  4) After writing all the telemetry IDs to the component, the
//     unit test will dump the hash table. The output looks like the following:
//        Slot: <n> - slot number
//        Entry - a bucket assigned to the slot
//        ... (Other buckets in the slot)
//     The number of buckets assigned to each slot can be checked for balance.
 
namespace {
 
    enum {
        TLMCHAN_NUM_TLM_HASH_SLOTS = 15, // !< Number of slots in the hash table.
                                        // Works best when set to about twice the number of components producing telemetry
        TLMCHAN_HASH_MOD_VALUE = 99,    // !< The modulo value of the hashing function.
                                        // Should be set to a little below the ID gaps to spread the entries around
 
        TLMCHAN_HASH_BUCKETS = 500       // !< Buckets assignable to a hash slot.
                                        // Buckets must be >= number of telemetry channels in system
    };
 
 
}
 
#endif /* TLMCHANIMPLCFG_HPP_ */