VCI - Virtual CAN Interface - Ixxat

Accessing the busThe specified delay time only represents a minimum, as it cannot be guaranteedthat the message can be transmitted to the bus after the time elapses. It mustalso be noted that when using several message channels on one CAN connectionthe specified time values cannot generally be observed, as the distributorprocesses all channels simultaneously. Applications that require an exact time sequencemust therefore use the CAN connection exclusively.3.1.4 Cyclic transmit listWith the optionally available cyclic transmit list, up to 16 messages per CAN connectioncan be transmitted cyclically, i.e. recurrently at certain time intervals. Hereit is possible that after each transmit process a certain part of a CAN message isautomatically incremented.As with the control unit, access to the cyclic transmit list is also restricted to onesingle application. It cannot therefore be used by more than one program simultaneously.The transmit list is opened by calling the function canSchedulerOpen. If the functionreturns a corresponding “access denied“ error code, the transmit list is alreadybeing used by another program. An opened transmit list is closed againand released for other applications with the function canSchedulerClose.A message object is added to the list with the function canSchedulerAddMessage.In addition to the handle of the list, the function expects a pointer to astructure of type CANCYCLICTXMSG that specifies the transmit object that is tobe added to the list. If run successfully, the function returns the list index of theadded transmit object.The cycle time of a transmit object is specified in number of ticks in the fieldwCycleTime of the structure CANCYCLICTXMSG. The value in this field must begreater than 0 and must not exceed the value in the field dwCmsMaxTicks of thestructure CANCAPABILITIES.The duration of a tick, or the cycle time t z of the transmit list can be calculatedwith the fields dwClockFreq and dwCmsDivisor of the structure CANCAPABILITIESaccording to the following formula.t z [s] = (dwCmsDivisor / dwClockFreq)The transmit task of the cyclic transmit list divides the time available to it into individualsections, so-called time slots. The duration of a time slot corresponds tothe duration of a tick or the cycle time. The number is shown in the fielddwCmsMaxTicks of the structure CANCAPABILITIES.25Copyright IXXAT Automation GmbH C-API Programming Manual, Version 1.5