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Added much of the text required to turn this into a real chapter.

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This commit is contained in:
Joel Sherrill
1999-06-04 13:37:23 +00:00
parent 0e99ecfcea
commit 6ff1ac4ebf
1 changed files with 195 additions and 52 deletions
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247
doc/itron3.0/semaphore.t
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@@ -49,21 +49,25 @@ is defined as follows:
@example
@group
/*
* Create Semaphore (cre_sem) Structure
*/
typedef struct t_csem @{
VP exinf; /* extended information */
ATR sematr; /* semaphore attributes */
/* Following is the extended function for [level X]. */
INT isemcnt; /* initial semaphore count */
INT maxsem; /* maximum semaphore count */
...
/* additional information may be included depending on the
implementation */
...
VP exinf; /* extended information */
ATR sematr; /* semaphore attributes */
/* Following is the extended function for [level X]. */
INT isemcnt; /* initial semaphore count */
INT maxsem; /* maximum semaphore count */
/* additional information may be included depending on the implementation */
@} T_CSEM;
sematr:
TA_TFIFO H'0...00 /* waiting tasks are handled by FIFO */
TA_TPRI H'0...01 /* waiting tasks are handled by priority */
/*
* sematr - Semaphore Attribute Values
*/
#define TA_TFIFO 0x00 /* waiting tasks are handled by FIFO */
#define TA_TPRI 0x01 /* waiting tasks are handled by priority */
@end group
@end example
@@ -72,7 +76,8 @@ where the meaning of each field is:
@table @b
@item exinf
is the extended information XXX
is for any extended information that the implementation may define.
This implementation does not use this field.
@item sematr
is the attributes for this semaphore. The only attributed
@@ -88,6 +93,24 @@ limit on the value taken by the semaphore.
@end table
@subsection Building a Semaphore's Attribute Set
In general, an attribute set is built by a bitwise OR
of the desired attribute components. The following table lists
the set of valid semaphore attributes:
@itemize @bullet
@item @code{TA_TFIFO} - tasks wait by FIFO
@item @code{TA_TPRI} - tasks wait by priority
@end itemize
Attribute values are specifically designed to be
mutually exclusive, therefore bitwise OR and addition operations
are equivalent as long as each attribute appears exactly once in
the component list.
@subsection T_RSEM Structure
The T_RSEM structure is filled in by the @code{ref_sem} service with
@@ -96,15 +119,15 @@ is defined as follows:
@example
@group
/*
* Reference Semaphore (ref_sem) Structure
*/
typedef struct t_rsem @{
VP exinf; /* extended information */
BOOL_ID wtsk; /* indicates whether or not there is a
waiting task */
INT semcnt; /* current semaphore count */
...
/* additional information may be included depending on the
implementation */
...
VP exinf; /* extended information */
BOOL_ID wtsk; /* indicates whether or not there is a waiting task */
INT semcnt; /* current semaphore count */
/* additional information may be included depending on the implementation */
@} T_RSEM;
@end group
@end example
@@ -112,17 +135,24 @@ typedef struct t_rsem @{
@table @b
@item exinf
is extended information.
is for any extended information that the implementation may define.
This implementation does not use this field.
@item wtsk
is TRUE when there is one or more task waiting on the semaphore.
It is FALSE if no tasks are currently waiting.
It is FALSE if no tasks are currently waiting. The meaning of this
field is allowed to vary between ITRON implementations. It may have
the ID of a waiting task, the number of tasks waiting, or a boolean
indication that one or more tasks are waiting.
@item semcnt
is the current semaphore count.
@end table
The information in this table is very volatile and should be used
with caution in an application.
@section Operations
@subsection Using as a Binary Semaphore
@@ -130,7 +160,11 @@ is the current semaphore count.
Creating a semaphore with a limit on the count of 1 effectively
restricts the semaphore to being a binary semaphore. When the
binary semaphore is available, the count is 1. When the binary
semaphore is unavailable, the count is 0.;
semaphore is unavailable, the count is 0.
Since this does not result in a true binary semaphore, advanced
binary features like the Priority Inheritance and Priority
Ceiling Protocols are not available.
@section System Calls
@@ -165,10 +199,13 @@ ER cre_sem(
@code{E_OK} - Normal Completion
@code{E_ID} - Invalid ID number (semid was invalid or could not be used)
@code{E_NOMEM} - Insufficient memory (Memory for control block cannot be
allocated)
@code{E_ID} - Invalid ID number (semid was invalid or could not be used)
@code{E_OACV} - Object access violation (A semid less than -4 was
specified from a user task. This is implementation dependent.)
@code{E_RSATR} - Reserved attribute (sematr was invalid or could not be
used)
@@ -176,9 +213,6 @@ used)
@code{E_OBJ} - Invalid object state (a semaphore of the same ID already
exists)
@code{E_OACV} - Object access violation (A semid less than -4 was
specified from a user task. This is implementation dependent.)
@code{E_PAR} - Parameter error (pk_csem is invalid and/or isemcnt or
maxsem is negative or invalid)
@@ -196,12 +230,43 @@ maxsem)
@subheading DESCRIPTION:
This routine creates a semaphore that resides on the local node. The
semaphore is initialized based on the attributes specified in the
@code{pk_csem} structure. The initial and maximum counts of the
semaphore are set based on the @code{isemcnt} and @code{maxsem} fields
in this structure.
Specifying @code{TA_TPRI} in the @code{sematr} field of the
semaphore attributes structure causes tasks
waiting for a semaphore to be serviced according to task
priority. When @code{TA_TFIFO} is selected, tasks are serviced in First
In-First Out order.
@subheading NOTES:
NONE
Multiprocessing is not supported. Thus none of the "EN_" status codes
will be returned.
All memory is preallocated for RTEMS ITRON objects. Thus, no dynamic
memory allocation is performed by @code{cre_sem} and the @code{E_NOMEM}
error can not be returned.
The ITRON specification calls for @code{E_OACV} to be returned for
some invalid semaphore IDs. This implementation returns @code{E_ID}
for all invalid IDs as there are no system reserved ITRON objects.
This directive will not cause the running task to be
preempted.
The following semaphore attribute constants are
defined by RTEMS:
@itemize @bullet
@item @code{TA_TFIFO} - tasks wait by FIFO
@item @code{TA_TPRI} - tasks wait by priority
@end itemize
@c
@c del_sem
@@ -225,8 +290,6 @@ ER del_sem(
@subheading STATUS CODES:
@subheading DESCRIPTION:
@code{E_OK} - Normal Completion
@code{E_ID} - Invalid ID number (semid was invalid or could not be used)
@@ -244,10 +307,35 @@ target node is specified.
was issued from a task in dispatch disabled state or from a
task-independent portion
@subheading DESCRIPTION:
This routine deletes the semaphore specified by @code{semid}.
All tasks blocked waiting to acquire the semaphore will be
readied and returned a status code which indicates that the
semaphore was deleted. The control block for this semaphore
is reclaimed by RTEMS.
@subheading NOTES:
NONE
Multiprocessing is not supported. Thus none of the "EN_" status codes
will be returned.
This implementation does not distinguish between an invalid ID (@code{E_ID})
and a valid id for a non-existent object (@code{E_NOEXS}). In addition,
there are no system reserved ITRON objects so the @code{E_OACV} error
is not returned. All IDs which do not correspond to an active user
created semaphore return @code{E_ID}.
The calling task will be preempted if it is enabled
by the task's execution mode and a higher priority local task is
waiting on the deleted semaphore. The calling task will NOT be
preempted if all of the tasks that are waiting on the semaphore
are remote tasks.
The calling task does not have to be the task that
created the semaphore. Any local task that knows the semaphore
id can delete the semaphore.
@c
@@ -296,8 +384,14 @@ task-independent portion
@subheading NOTES:
NONE
Multiprocessing is not supported. Thus none of the "EN_" status codes
will be returned.
This implementation does not distinguish between an invalid ID (@code{E_ID})
and a valid id for a non-existent object (@code{E_NOEXS}). In addition,
there are no system reserved ITRON objects so the @code{E_OACV} error
is not returned. All IDs which do not correspond to an active user
created semaphore return @code{E_ID}.
@c
@c wai_sem
@@ -331,16 +425,12 @@ does not exist)
@code{E_OACV} - Object access violation (A semid less than -4 was
specified from a user task. This is implementation dependent.)
@code{E_PAR} - Parameter error (tmout is -2 or less)
@code{E_DLT} - The object being waited for was deleted (the specified
semaphore was deleted while waiting)
@code{E_RLWAI} - Wait state was forcibly released (rel_wai was received
while waiting)
@code{E_TMOUT} - Polling failure or timeout exceeded
@code{E_CTX} - Context error (issued from task-independent portions or a
task in dispatch disabled state)
@@ -351,13 +441,26 @@ target node is specified.
and/or transmission packet format was specified as a parameter (a value
outside supported range was specified for tmout)
@subheading DESCRIPTION:
This routine attempts to acquire the semaphore specified by @code{semid}.
If the semaphore is available (i.e. positive semaphore count), then the
semaphore count is decremented and the calling task returns immediately.
Otherwise the calling tasking is blocked until the semaphore is released
by a subsequent invocation of @code{sig_sem}.
@subheading NOTES:
NONE
Multiprocessing is not supported. Thus none of the "EN_" status codes
will be returned.
This implementation does not distinguish between an invalid ID (@code{E_ID})
and a valid id for a non-existent object (@code{E_NOEXS}). In addition,
there are no system reserved ITRON objects so the @code{E_OACV} error
is not returned. All IDs which do not correspond to an active user
created semaphore return @code{E_ID}.
If the semaphore is not available, then the calling task will be blocked.
@c
@c preq_sem
@@ -391,14 +494,6 @@ does not exist)
@code{E_OACV} - Object access violation (A semid less than -4 was
specified from a user task. This is implementation dependent.)
@code{E_PAR} - Parameter error (tmout is -2 or less)
@code{E_DLT} - The object being waited for was deleted (the specified
semaphore was deleted while waiting)
@code{E_RLWAI} - Wait state was forcibly released (rel_wai was received
while waiting)
@code{E_TMOUT} - Polling failure or timeout exceeded
@code{E_CTX} - Context error (issued from task-independent portions or a
@@ -411,13 +506,26 @@ target node is specified.
and/or transmission packet format was specified as a parameter (a value
outside supported range was specified for tmout)
@subheading DESCRIPTION:
This routine attempts to acquire the semaphore specified by @code{semid}.
If the semaphore is available (i.e. positive semaphore count), then the
semaphore count is decremented and the calling task returns immediately.
Otherwise, the @code{E_TMOUT} error is returned to the calling task to
indicate the semaphore is unavailable.
@subheading NOTES:
NONE
Multiprocessing is not supported. Thus none of the "EN_" status codes
will be returned.
This implementation does not distinguish between an invalid ID (@code{E_ID})
and a valid id for a non-existent object (@code{E_NOEXS}). In addition,
there are no system reserved ITRON objects so the @code{E_OACV} error
is not returned. All IDs which do not correspond to an active user
created semaphore return @code{E_ID}.
This routine will not cause the running task to be preempted.
@c
@c twai_sem
@@ -472,13 +580,35 @@ target node is specified.
and/or transmission packet format was specified as a parameter (a value
outside supported range was specified for tmout)
@subheading DESCRIPTION:
This routine attempts to acquire the semaphore specified by @code{semid}.
If the semaphore is available (i.e. positive semaphore count), then the
semaphore count is decremented and the calling task returns immediately.
Otherwise the calling tasking is blocked until the semaphore is released
by a subsequent invocation of @code{sig_sem} or the timeout period specified
by @code{tmout} milliseconds is exceeded. If the timeout period is exceeded,
then the @code{E_TMOUT} error is returned.
By specifiying @code{tmout} as @code{TMO_FEVR}, this routine has the same
behavior as @code{wai_sem}. Similarly, by specifiying @code{tmout} as
@code{TMO_POL}, this routine has the same behavior as @code{preq_sem}.
@subheading NOTES:
NONE
Multiprocessing is not supported. Thus none of the "EN_" status codes
will be returned.
This implementation does not distinguish between an invalid ID (@code{E_ID})
and a valid id for a non-existent object (@code{E_NOEXS}). In addition,
there are no system reserved ITRON objects so the @code{E_OACV} error
is not returned. All IDs which do not correspond to an active user
created semaphore return @code{E_ID}.
This routine may cause the calling task to block.
A clock tick is required to support the timeout functionality of
this routine.
@c
@c ref_sem
@@ -529,7 +659,20 @@ value outside supported range was specified for exinf, wtsk or semcnt)
@subheading DESCRIPTION:
This routine returns status information on the semaphore specified
by @code{semid}. The @code{pk_rsem} structure is filled in by
this service call.
@subheading NOTES:
NONE
Multiprocessing is not supported. Thus none of the "EN_" status codes
will be returned.
This implementation does not distinguish between an invalid ID (@code{E_ID})
and a valid id for a non-existent object (@code{E_NOEXS}). In addition,
there are no system reserved ITRON objects so the @code{E_OACV} error
is not returned. All IDs which do not correspond to an active user
created semaphore return @code{E_ID}.
This routine will not cause the running task to be preempted.