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XCP (or) "Universal Measurement and Calibration Protocol" is a network protocol originating from ASAM for connecting measurement/calibration systems to electronic control units, ECUs. It enables read and write access to variables and memory contents of micro-controller systems at run-time. To achieve independence from a specific physical transport layer, XCP was subdivided into a protocol layer and a transport layer. Depending on the transport layer, one refers to XCP on CAN, XCP on Ethernet, etc. and can be extended to future transport layers

The  measurement  and  calibration  system  assumes  the  role  of  XCP  master, while the ECU operates as a slave. The master and slave each communicate by XCP driver. There is an ECU description file (in A2L format) for each slave, which specifies  associations  between  symbolic  variable  names  and  their  address  ranges,  physical  meanings  of  the  data  and  the  checksum  method used. The XCP master can read out all necessary information from these A2L description files.

A key functionality of XCP is that it enables read and write access to the memory of the Slave. One of the great strengths of XCP  lies  in  acquiring  measured  values  from  RAM  which  change  synchronously  to  process  flows  or  events  in  the  ECU.  This  lets  users  evaluate  direct  relationships  between  time-based  process  flows in the ECU and the changing values. These are referred to as event-synchronous measurements. Write  access  lets  the  user  optimize  parameters  of  algorithms  in  the  Slave. 

The  accesses  are  address-oriented,  i.e.  the  communication  between  Master  and  Slave  references  addresses  in  memory.  So,  the  measurement  of  a  parameter  is  essentially  implemented  as  a  request  of  the  Master to the Slave: “Give me the value of memory location 0x1234”. Calibration of a parameter – the write access – to the Slave means: “Set the value at address 0x9876 to 5”.

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