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<!-- Copyright (C) 2003 Red Hat, Inc. --><!-- This material may be distributed only subject to the terms --><!-- and conditions set forth in the Open Publication License, v1.0 --><!-- or later (the latest version is presently available at --><!-- http://www.opencontent.org/openpub/). --><!-- Distribution of the work or derivative of the work in any --><!-- standard (paper) book form is prohibited unless prior --><!-- permission is obtained from the copyright holder. --><HTML><HEAD><TITLE>礗TRON and eCos</TITLE><meta name="MSSmartTagsPreventParsing" content="TRUE"><METANAME="GENERATOR"CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+"><LINKREL="HOME"TITLE="eCos Reference Manual"HREF="ecos-ref.html"><LINKREL="UP"TITLE="礗TRON API"HREF="compat-uitron-microitron-api.html"><LINKREL="PREVIOUS"TITLE="礗TRON API"HREF="compat-uitron-microitron-api.html"><LINKREL="NEXT"TITLE="Task Management Functions"HREF="compat-uitron-task-management-functions.html"></HEAD><BODYCLASS="SECT1"BGCOLOR="#FFFFFF"TEXT="#000000"LINK="#0000FF"VLINK="#840084"ALINK="#0000FF"><DIVCLASS="NAVHEADER"><TABLESUMMARY="Header navigation table"WIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><THCOLSPAN="3"ALIGN="center">eCos Reference Manual</TH></TR><TR><TDWIDTH="10%"ALIGN="left"VALIGN="bottom"><AHREF="compat-uitron-microitron-api.html"ACCESSKEY="P">Prev</A></TD><TDWIDTH="80%"ALIGN="center"VALIGN="bottom">Chapter 32. µITRON API</TD><TDWIDTH="10%"ALIGN="right"VALIGN="bottom"><AHREF="compat-uitron-task-management-functions.html"ACCESSKEY="N">Next</A></TD></TR></TABLE><HRALIGN="LEFT"WIDTH="100%"></DIV><DIVCLASS="SECT1"><H1CLASS="SECT1"><ANAME="COMPAT-UITRON-OVER-ECOS">µITRON and <SPANCLASS="emphasis"><ICLASS="EMPHASIS">eCos</I></SPAN></H1><P>The <SPANCLASS="emphasis"><ICLASS="EMPHASIS">eCos</I></SPAN> kernel implements the functionalityused by the µITRON compatibility subsystem.The configuration of the kernel influences the behavior of µITRONprograms.</P><P>In particular, the default configuration has time slicing(also known as round-robin scheduling) switched on; this means thata task can be moved from <TTCLASS="VARNAME">RUN</TT> stateto <TTCLASS="VARNAME">READY</TT> state at any time, inorder that one of its peers may run. This is not strictly conformantto the µITRON specification, whichstates that timeslicing may be implemented by periodically issuinga <TTCLASS="LITERAL">rot_rdq(0)</TT> call fromwithin a periodic task or cyclic handler; otherwise it is expectedthat a task runs until it is pre-empted in consequence of synchronizationor communication calls it makes, or the effects of an interruptor other external event on a higher priority task cause that taskto become <TTCLASS="VARNAME">READY</TT>. To disable timeslicingfunctionality in the kernel and µITRONcompatibility environment, please disable the <TTCLASS="LITERAL">CYGSEM_KERNEL_SCHED_TIMESLICE</TT>configuration option in the kernel package. A description of kernelscheduling is in <AHREF="kernel-overview.html">Kernel Overview</A>. </P><P>For another example, the semantics of task queueing when waitingon a synchronization object depend solely on the way the underlyingkernel is configured. As discussed above, the multi-level queuescheduler is the only one which is µITRONcompliant, and it queues waiting tasks in FIFO order. Future releasesof that scheduler might be configurable to support priority orderingof task queues. Other schedulers might be different again: for examplethe bitmap scheduler can be used with the µITRONcompatibility layer, even though it only allows one task at eachpriority and as such is not µITRONcompliant, but it supports only priority ordering of task queues.So which queueing scheme is supported is not really a property ofthe µITRON compatibility layer; itdepends on the kernel. </P><P>In this version of the µITRONcompatibility layer, the calls to disable and enable schedulingand interrupts (<TTCLASS="FUNCTION">dis_dsp()</TT>,<TTCLASS="FUNCTION">ena_dsp()</TT>, <TTCLASS="FUNCTION">loc_cpu()</TT>and <TTCLASS="FUNCTION">unl_cpu()</TT>)call underlying kernel functions; in particular, the <TTCLASS="FUNCTION">xxx_dsp()</TT> functionslock the scheduler entirely, which prevents dispatching of DSRs; functionsimplemented by DSRs include clock counters and alarm timers. Thus time “stops” whiledispatching is disabled with <TTCLASS="FUNCTION">dis_dsp()</TT>. </P><P>Like all parts of the <SPANCLASS="emphasis"><ICLASS="EMPHASIS">eCos</I></SPAN> system, thedetailed semantics of the µITRON layerare dependent on its configuration and the configuration of other componentsthat it uses. The µITRON configurationoptions are all defined in the file <TTCLASS="FILENAME">pkgconf/uitron.h</TT>,and can be set using the configuration tool or editing the<TTCLASS="FILENAME">.ecc</TT>file in your build directory by hand. </P><P>An important configuration option for the µITRONcompatibility layer is “Option: Return Error Codes for Bad Params”(<TTCLASS="LITERAL">CYGSEM_UITRON_BAD_PARAMS_RETURN_ERRORS</TT>), which allows a lot of the errorchecking code in the µITRON compatibility layer tobe removed. Of course this leaves a program open to undetected errors,so it should only be used once an application is fully debugged andtested. Its benefits include reduced code size and faster execution.However, it affects the API significantly, in that with this optionenabled, bad calls do not return errors, but cause an assertfailure (if that is itself enabled) or malfunction internally. Thereis discussion in more detail about this in each section below.</P><P>We now give a brief description of the µITRONfunctions which are implemented in this release. Note that all Cand C++ source files should have the following <TTCLASS="LITERAL">#include</TT> statement: </P><TABLEBORDER="5"BGCOLOR="#E0E0F0"WIDTH="70%"><TR><TD><PRECLASS="PROGRAMLISTING">#include <cyg/compat/uitron/uit_func.h></PRE></TD></TR></TABLE></DIV><DIVCLASS="NAVFOOTER"><HRALIGN="LEFT"WIDTH="100%"><TABLESUMMARY="Footer navigation table"WIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top"><AHREF="compat-uitron-microitron-api.html"ACCESSKEY="P">Prev</A></TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><AHREF="ecos-ref.html"ACCESSKEY="H">Home</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top"><AHREF="compat-uitron-task-management-functions.html"ACCESSKEY="N">Next</A></TD></TR><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top">µITRON API</TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><AHREF="compat-uitron-microitron-api.html"ACCESSKEY="U">Up</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top">Task Management Functions</TD></TR></TABLE></DIV></BODY></HTML>⌨️ 快捷键说明
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