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embedded_systems:ethercat:ethercatinterface:understanding_ethercatinterface [2019-04-16 10:53]
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-====== Understanding EtherCatInterface ====== 
-===== ecmasterlib ===== 
-The //"​ecmasterlib"//​ provides a callback function (''​void callbackFct(...)''​) which is called by the Acontis stack once per EtherCAT cycle. 
-This method: 
-  * Copies the received data from the stack into the receive buffer of //"​ecmasterlib"//​ 
-  * Copies the data to be sent from the send buffer of //"​ecmasterlib"//​ to the stack. 
-The receive and send buffers of //"​ecmasterlib"//​ are byte arrays (''​uint8_t* inBuffer; uint8_t* outBuffer;''​) which are the same size as the PDOs. 
-The //"​ecmasterlib"//​ also provides a condition variable (''​std::​condition_variable cv;''​) to synchronize the user application (i.e. EEROS). 
-When an //"​ecmasterlib"//​ object is created, an instance (monotonic) is created. 
-The stack is started exactly as in the //"​EcMasterDemoDC"//​ of Acontis. 
-===== EtherCatInterfaceBase ===== 
-This is the base class for all interface classes. 
-It mainly provides ''​set''​ and ''​get''​ methods for 8, 16, and 32 bit long data. 
-The get methods calculate the correct offset of the receive buffer of the //"​ecmasterlib"//​ and returns the data. 
-The set methods also calculate the offset and write the data into the transmit buffer of //"​ecmasterlib"//​. 
-==== EtherCatInterfaceBase_config.hpp ==== 
-===== EtherCatInterfaceElmo ===== 
-The //"​EtherCatInterfaceElmo"//​ is especially designed for the Gold Twitter drives from Elmo. 
-It consists of the following components: 
-  * EtherCatInterfaceElmo.hpp 
-  * EtherCatInterfaceElmo.cpp 
-  * EtherCatInterfaceElmo_config.hpp 
-The //"​EtherCatInterfaceElmo.hpp"//​ declares all methods of the interface. 
-The low level methods ('​ll_'​-prefix) are at the bottom of the page. 
-These low level methods read and write individual data objects to/from the stack. 
-Which objects are available and their file type must be read from the documentation of the manufacturer of the EtherCAT slave. 
-Each data object has its own method. 
-Where a data object is located in the PDO depends on the ENI file used. 
-These offsets must be read from the ENI file and configured in //"​EtherCatInterfaceElmo_config.hpp"//​. 
-All methods above the low level methods are optional. 
-They contain a certain degree of intelligence and simplify the interface to the user application. 
-==== Blocking functions ==== 
-Methods in the interface must never be **blocking**. 
-Some advanced functions may take several cycles. 
-They are only completed when they return ''​true''​. 
-These methods must be called again in each cycle until they return ''​true''​. 
-==== EtherCatInterfaceElmo_config.hpp ==== 
-This is configuration file has do be adapted depending on the EtherCAT network. 
-The most important part of this file is the offset definition of all PDO offset. 
-Before you start your application,​ you have to define all PDO offsets of your network. 
-Be aware that EtherCATInterface assumes that all drives send the identical variables via PDO. 
-With the current implementation it is not possible to send different variables for different drives. 
-If a variable is not available, the offset is set to '​-1'​. 
-The methods which would use a unavailable variable will throw an error if called.