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git-svn-id: svn://svn.code.sf.net/p/chibios/svn/trunk@657 35acf78f-673a-0410-8e92-d51de3d6d3f4

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docs/src/jitter.dox
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/** /**
* @page article_jitter Minimizing Jitter * @page article_jitter Response Time and Jitter
* @{ * @{
* Response time jitter is one of the more sneaky source of problems when * Response time jitter is one of the most sneaky source of problems when
* designing a real time system. When using a RTOS like ChibiOS/RT one must * designing a real time system. When using a RTOS like ChibiOS/RT one must
* be aware of what Jitter is and how it can affect the performance of the * be aware of what Jitter is and how it can affect the performance of the
* system.<br> * system.<br>
* A good place to start is this * A good place to start is this
* <a href="http://en.wikipedia.org/wiki/Jitter">Wikipedia article</a>. * <a href="http://en.wikipedia.org/wiki/Jitter">Wikipedia article</a>.
* <h2>Jitter sources under ChibiOS/RT</h2> *
* <h2>Jitter Sources</h2>
* Under ChibiOS/RT (or any other similar RTOS) there are several jitter * Under ChibiOS/RT (or any other similar RTOS) there are several jitter
* possible sources: * possible sources:
* -# Hardware interrupt latency. * -# Hardware interrupts latency.
* -# Interrupt service time. * -# Interrupts service time and priority.
* -# Kernel lock zones. * -# Kernel lock zones.
* -# Higher priority threads activity. * -# Higher priority threads activity.
* *
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* For each of the previously described jitter source there are possible * For each of the previously described jitter source there are possible
* mitigation actions. * mitigation actions.
* *
* <h3>Hardware interrupt latency</h3> * <h3>Hardware interrupts latency</h3>
* This parameter is pretty much fixed and a characteristic of the system. * This parameter is pretty much fixed and a characteristic of the system.
* Possible actions include higher clock speeds or switch to an hardware * Possible actions include higher clock speeds or switch to an hardware
* architecture more efficient at interrupt handling, as example, the * architecture more efficient at interrupt handling, as example, the
* ARM Cortex-M3 core present in the STM32 family is very efficient at * ARM Cortex-M3 core present in the STM32 family is very efficient at that.
* interrupt handling.
* *
* <h3>Interrupt service time</h3> * <h3>Interrupts service time and priority</h3>
* This is the execution time of interrupt handlers, this time includes: * This is the execution time of interrupt handlers, this time includes:
* - Fixed handler overhead, as example registers stacking/unstacking. * - Fixed handler overhead, as example registers stacking/unstacking.
* - Interrupt specific service time, as example, in a serial driver, this is * - Interrupt specific service time, as example, in a serial driver, this is