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embedded_systems:ethercat:choose_linux_master [2019-01-08 17:09] – angelegt mgehrig2 | embedded_systems:ethercat:choose_linux_master [2019-02-08 14:33] – mgehrig2 | ||
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====== Choose a Linux Master ====== | ====== Choose a Linux Master ====== | ||
+ | ===== Realtime capability ===== | ||
+ | Depending on the requirements, | ||
+ | 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: | ||
+ | A time buffer, which is larger than the largest expected jitter, has to be used. | ||
+ | If the time buffer is smaller, 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 also 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: | ||
+ | |||
+ | [[software: | ||
+ | There are also some tips on how to find a PC with good real-time performance. | ||