Since its initial release, µC/OS-III iterated through several methods of managing task delays and timeouts. V3.04.00 introduced the concept of a delta-list, which reduced the overhead involved in checking for timeouts and expired delays; however, that initial implementation maintained two separate lists for tracking timeouts and delays. V3.07.00 merged the two lists into one, called OSTickList, in order to reduce memory consumption and overhead simplify some of the internals details involved with maintaining multiple tick lists.
Tasks are automatically inserted into the tick list when the application programmer calls an OSTimeDly???() function, or when an OS???Pend() call is made with a non-zero timeout value. A task is usually removed from the tick list by the tick ISR once its delay or timeout has expired. It may also be removed if the time delay is resumed or the pend with timeout is aborted.
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