# SYS\_FMU\_TASK affects output message rates

**URL:** <https://discuss.px4.io/t/sys-fmu-task-affects-output-message-rates/8752>\
**Category:** Uncategorized\
**Created:** [December 5, 2018, 5:11pm UTC](https://discuss.px4.io/t/sys-fmu-task-affects-output-message-rates/8752 "2018-12-05T17:11:34Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![rcpx4](https://discuss.px4.io/letter_avatar_proxy/v4/letter/r/bcef8e/32.png) [@rcpx4](https://discuss.px4.io/u/rcpx4)\
**Post date:** [December 5, 2018, 5:11pm UTC](https://discuss.px4.io/t/sys-fmu-task-affects-output-message-rates/8752/1 "2018-12-05T17:11:34Z")

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When I set SYS\_FMU\_TASK to 0, actuator\_outputs and multirotor\_motor\_limits messages are output at ~330Hz.  
When I set SYS\_FMU\_TASK to 1, actuator\_outputs and multirotor\_motor\_limits messages are output at ~275Hz.

The [SYS\_FMU\_TASK](https://dev.px4.io/en/advanced/parameter_reference.html#SYS_FMU_TASK) description implies that latency would be affected. But I didn’t realize that it would result in different output rates for these messages.

Is this the expected behavior?

Thanks.

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**Author:** ![JulianOes](https://discuss.px4.io/user_avatar/discuss.px4.io/julianoes/32/30_2.png) [@JulianOes](https://discuss.px4.io/u/JulianOes)\
**Post date:** [December 5, 2018, 5:28pm UTC](https://discuss.px4.io/t/sys-fmu-task-affects-output-message-rates/8752/2 "2018-12-05T17:28:38Z")

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Interesting. @bkueng does that make sense to you?

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**Author:** ![bkueng](https://discuss.px4.io/letter_avatar_proxy/v4/letter/b/2bfe46/32.png) [@bkueng](https://discuss.px4.io/u/bkueng)\
**Post date:** [December 5, 2018, 6:26pm UTC](https://discuss.px4.io/t/sys-fmu-task-affects-output-message-rates/8752/3 "2018-12-05T18:26:18Z")

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Yes: if disabled, `fmu` is scheduled at a fixed frequency, around 330Hz. If enabled, it runs in sync with the publication of actuator controls, which is what you see.  
Note that the lower frequency is actually not worse, because running faster than actuator controls gets updated does not improve the result. If running on the work queue it just runs a bit faster to account for scheduling overhead.  
In (near) future we want to increase the actuator controls rate to 1kHz.