Bosch probably did write the entire package or most of it. In some cases the customer (OEM) will give a non-standard algorithm to Bosch for implementation although potentially the OEM could implement and integrate it - it depends on the commercial relationship between the EMS supplier and the OEM. Examples are things like different evaporative monitoring systems or varying VVT systems or perhaps intake manifold arrangements that cause strange sensor readings - things that do not follow the 'standard' algorithms that Bosch has developed and used. That being said, Bosch will compile a software version for a specific application with other things taken out to save space. For example on applications with an LSU4.2 sensor they won't compile-in the LSF4.2 O2 sensor algorithm thus the code for my 2001 GTI with a LSF4.2 won't contain the same functions as the 2000 GTI with the LSU4.2 - and all of the memory locations in the calibration file are different. Since the calibration tables are now different in size (because of one different algorithms) all of the memory locations of every table - or at least ones after the modifications - will be different, too. The compiler basically tosses things 'willy-nilly' in memory and in the compilation process Bosch will produce a calibration description file (A2L) that contains the addresses and dimensions of each table. Since the file generation is automatic it is not a pain like it is for tuners that find addresses by hand and generate their own files. Then Bosch will generate a document with calibration procedures for that ECM software variant, send a HEX and A2L file to the OEM. If the OEM has calibration responsibility than the OEM takes care of actually doing the tuning while following the Bosch procedures. This not only includes the procedures in the calibration manual but also in every sensor application manual - for example, O2 sensor dewpoint management is covered by a separate calibration document. An OEM may contract Bosch (or Delphi or Visteon or Valeo) to do a turnkey and in that case the EMS engineers will do the calibration and hand over a completed firmware and calibration file. Hope that answers your question.