http://embeddedgurus.com/barr-code/2009/10/slack-scheduling-vs-rate-monotonic-analysis/ A Blog by Michael Barr Tue, 24 Jan 2012 21:58:05 +0000 hourly 1 http://wordpress.org/?v=3.2.1 http://embeddedgurus.com/barr-code/2009/10/slack-scheduling-vs-rate-monotonic-analysis/comment-page-1/#comment-78 Michael Barr Fri, 02 Oct 2009 18:25:04 +0000 http://www.gfcdev.org/test-stack/2009/10/02/slack-scheduling-vs-rate-monotonic-analysis/#comment-78 A minor point in this article prompted one cool thought that I had never had. When using RMA to assign task priorities with an RTOS, such as Micrium's uC/OS-II, that treats tasks with lower integer priority numbers as more important, it may sometimes be possible to actually use the worst-case (most frequent) inter-arrival time as the priority number.For example, if you had tasks with recurring 1ms, 3ms, 17ms, and 1s worst-case periods you could assign their priorities like this:enum { taskA_prio = 1, taskX_prio = 3, taskB_prio = 17, taskW_prio = 1000 } task_prios;The most frequent task always gets higher relative priority under RMA.Of course, this also requires your problem domain to feature timing resolution (e.g., milliseconds) and range (e.g., 0-1000) that is both human readable and fits within the integer width of your RTOSes priority parameter. uC/OS-II couldn't handle this example, because it uses an 8-bit priority. uC/OS-III, though, could handle that scenerio. A minor point in this article prompted one cool thought that I had never had. When using RMA to assign task priorities with an RTOS, such as Micrium's uC/OS-II, that treats tasks with lower integer priority numbers as more important, it may sometimes be possible to actually use the worst-case (most frequent) inter-arrival time as the priority number.For example, if you had tasks with recurring 1ms, 3ms, 17ms, and 1s worst-case periods you could assign their priorities like this:enum { taskA_prio = 1, taskX_prio = 3, taskB_prio = 17, taskW_prio = 1000 } task_prios;The most frequent task always gets higher relative priority under RMA.Of course, this also requires your problem domain to feature timing resolution (e.g., milliseconds) and range (e.g., 0-1000) that is both human readable and fits within the integer width of your RTOSes priority parameter. uC/OS-II couldn't handle this example, because it uses an 8-bit priority. uC/OS-III, though, could handle that scenerio.

]]>