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<HTML
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><HEAD
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><TITLE
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>µITRON and eCos</TITLE
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HREF="ecos-ref.html"><LINK
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REL="UP"
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TITLE="µITRON API"
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HREF="compat-uitron-microitron-api.html"><LINK
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HREF="compat-uitron-microitron-api.html"><LINK
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REL="NEXT"
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TITLE="Task Management Functions"
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HREF="compat-uitron-task-management-functions.html"></HEAD
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><TH
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>eCos Reference Manual</TH
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></TR
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><TR
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><TD
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WIDTH="10%"
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VALIGN="bottom"
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><A
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HREF="compat-uitron-microitron-api.html"
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ACCESSKEY="P"
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>Prev</A
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></TD
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><TD
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WIDTH="80%"
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ALIGN="center"
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VALIGN="bottom"
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>Chapter 32. µITRON API</TD
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><TD
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="compat-uitron-task-management-functions.html"
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>Next</A
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CLASS="SECT1"
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><H1
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CLASS="SECT1"
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><A
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NAME="COMPAT-UITRON-OVER-ECOS">µITRON and <SPAN
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CLASS="emphasis"
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><I
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CLASS="EMPHASIS"
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>eCos</I
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></SPAN
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></H1
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><P
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>The <SPAN
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CLASS="emphasis"
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><I
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CLASS="EMPHASIS"
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>eCos</I
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></SPAN
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> kernel implements the functionality
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used by the µITRON compatibility subsystem.
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The configuration of the kernel influences the behavior of µITRON
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programs.</P
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><P
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>In particular, the default configuration has time slicing
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(also known as round-robin scheduling) switched on; this means that
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a task can be moved from <TT
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CLASS="VARNAME"
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>RUN</TT
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> state
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to <TT
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CLASS="VARNAME"
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>READY</TT
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> state at any time, in
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order that one of its peers may run. This is not strictly conformant
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to the µITRON specification, which
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states that timeslicing may be implemented by periodically issuing
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a <TT
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CLASS="LITERAL"
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>rot_rdq(0)</TT
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> call from
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within a periodic task or cyclic handler; otherwise it is expected
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that a task runs until it is pre-empted in consequence of synchronization
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or communication calls it makes, or the effects of an interrupt
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or other external event on a higher priority task cause that task
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to become <TT
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CLASS="VARNAME"
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>READY</TT
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>. To disable timeslicing
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functionality in the kernel and µITRON
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compatibility environment, please disable the
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<TT
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CLASS="LITERAL"
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>CYGSEM_KERNEL_SCHED_TIMESLICE</TT
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>
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configuration option in the kernel package. A description of kernel
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scheduling is in <A
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HREF="kernel-overview.html"
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>Kernel Overview</A
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>. </P
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><P
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>For another example, the semantics of task queueing when waiting
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on a synchronization object depend solely on the way the underlying
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kernel is configured. As discussed above, the multi-level queue
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scheduler is the only one which is µITRON
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compliant, and it queues waiting tasks in FIFO order. Future releases
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of that scheduler might be configurable to support priority ordering
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of task queues. Other schedulers might be different again: for example
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the bitmap scheduler can be used with the µITRON
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compatibility layer, even though it only allows one task at each
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priority and as such is not µITRON
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compliant, but it supports only priority ordering of task queues.
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So which queueing scheme is supported is not really a property of
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the µITRON compatibility layer; it
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depends on the kernel. </P
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><P
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>In this version of the µITRON
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compatibility layer, the calls to disable and enable scheduling
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and interrupts (<TT
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CLASS="FUNCTION"
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>dis_dsp()</TT
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>,
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<TT
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CLASS="FUNCTION"
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>ena_dsp()</TT
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>, <TT
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CLASS="FUNCTION"
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>loc_cpu()</TT
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>
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and <TT
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CLASS="FUNCTION"
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>unl_cpu()</TT
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>)
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call underlying kernel functions; in particular, the <TT
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CLASS="FUNCTION"
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>xxx_dsp()</TT
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> functions
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lock the scheduler entirely, which prevents dispatching of DSRs; functions
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implemented by DSRs include clock counters and alarm timers. Thus time “stops” while
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dispatching is disabled with <TT
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CLASS="FUNCTION"
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>dis_dsp()</TT
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>. </P
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><P
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>Like all parts of the <SPAN
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CLASS="emphasis"
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><I
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CLASS="EMPHASIS"
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>eCos</I
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></SPAN
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> system, the
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detailed semantics of the µITRON layer
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are dependent on its configuration and the configuration of other components
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that it uses. The µITRON configuration
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options are all defined in the file <TT
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CLASS="FILENAME"
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>pkgconf/uitron.h</TT
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>,
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and can be set using the configuration tool or editing the
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<TT
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CLASS="FILENAME"
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>.ecc</TT
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>
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file in your build directory by hand. </P
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><P
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>An important configuration option for the µITRON
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compatibility layer is “Option: Return Error Codes for Bad Params”
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(
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<TT
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CLASS="LITERAL"
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>CYGSEM_UITRON_BAD_PARAMS_RETURN_ERRORS</TT
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>
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), which allows a lot of the error
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checking code in the µITRON compatibility layer to
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be removed. Of course this leaves a program open to undetected errors,
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so it should only be used once an application is fully debugged and
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tested. Its benefits include reduced code size and faster execution.
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However, it affects the API significantly, in that with this option
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enabled, bad calls do not return errors, but cause an assert
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failure (if that is itself enabled) or malfunction internally. There
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is discussion in more detail about this in each section below.</P
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><P
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>We now give a brief description of the µITRON
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functions which are implemented in this release. Note that all C
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and C++ source files should have the following <TT
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CLASS="LITERAL"
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>#include</TT
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> statement: </P
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><TD
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><PRE
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CLASS="PROGRAMLISTING"
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>#include <cyg/compat/uitron/uit_func.h></PRE
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>µITRON API</TD
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