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embedded_systems:ethercat:choose_linux_master [2019-01-08 17:09] – angelegt mgehrig2embedded_systems:ethercat:choose_linux_master [2023-04-11 11:20] (aktuell) Urs Graf
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-====== Choose a Linux Master ======+====== Choose a Linux master ====== 
 +===== Overview ===== 
 +The linux master is a PC with Linux installed. 
 +The kernel is patched with the rt preempt patch to make the system real-time capable. 
 +The Ethernet port is used to connect the PC with the EtherCAT network.
  
  
 +===== Realtime capability =====
 +Depending on the requirements, the PC must have very good real-time properties.
 +
 +Very good real-time behavior (max. jitter < 30 usec) is required if:
 +  * The Linux master must set the clock. E.g. if no distributed clock is used and the bus cannot be synchronized with a slave. See [[embedded_systems:ethercat:understanding_ethercat:understanding_sync_with_dc|Understanding Synchronisation with Distributed Clock]]s for more information.
 +
 +A time buffer, which is larger than the largest expected jitter, has to be used.
 +If the time buffer is too small, then in some cases the timing cannot be met and the data from this cycle is lost.
 +
 +The smaller this time buffer is, the more time is available for calculations on the master.
 +However, the buffer must be large enough so that the system can reliably meet the timing deadlines.
 +A good real-time behavior enables a smaller time buffer.
 +
 +The minimum cycletime, and thus the maximum frequency of the control loop, is mainly given by this time buffer plus the calculation time (EEROS).
 +
 +TODO graphic time management on master
 +
 +See [[software:linux:realtime:benchmark|Benchmark realtime system]] to benchmark your master.
 +
 +[[software:linux:realtime:testeddevices|This list]] contains some tested systems.
 +There are also some tips on how to find a PC with good real-time performance.
  
  
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 Check with your contact from Acontis if this ethernet controller is suitable for one of there link layers. Check with your contact from Acontis if this ethernet controller is suitable for one of there link layers.
-Check chapter 2.3.1.3 of the Acontis {{:embedded_systems:ethercat:ec-master_classb.pdf|stack documentation}}.+Check chapter 2.3.1.3 of the Acontis {{:embedded_systems:ethercat:ec-master_classb.pdf|stack documentation}} for supported network controllers.
  
 The //"emllI8254x Intel Pro/1000"// is one of the most used layers. The //"emllI8254x Intel Pro/1000"// is one of the most used layers.