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authorJoel Sherrill <joel.sherrill@OARcorp.com>1999-07-06 14:52:55 +0000
committerJoel Sherrill <joel.sherrill@OARcorp.com>1999-07-06 14:52:55 +0000
commit2aab33e561dc711b3f708e9aa63c680e2d044bb7 (patch)
treeff804d8ca474fd3f08b6b84040f32842e300e531 /doc
parentbae90e17a7acb331663fa6770d44f714a4cc2d32 (diff)
downloadrtems-2aab33e561dc711b3f708e9aa63c680e2d044bb7.tar.bz2
From Fei Ling <fling@cs.uah.edu>.
Diffstat (limited to 'doc')
-rw-r--r--doc/itron3.0/msgbuffer.t543
1 files changed, 524 insertions, 19 deletions
diff --git a/doc/itron3.0/msgbuffer.t b/doc/itron3.0/msgbuffer.t
index a6fc84fd37..51f86adc4a 100644
--- a/doc/itron3.0/msgbuffer.t
+++ b/doc/itron3.0/msgbuffer.t
@@ -10,8 +10,9 @@
@section Introduction
-The
-message buffer manager is ...
+The message buffer manager provides functions to create, delete, and
+control of message buffers. This manager is based on the ITRON 3.0
+standard.
The services provided by the message buffer manager are:
@@ -29,6 +30,100 @@ The services provided by the message buffer manager are:
@section Background
+@subsection T_CMBF Structure
+
+The T_CMBF structure is used to define the characteristics of a message
+buffer and passed as an argument to the @code{cre_mbf} routine. This
+structure is defined as:
+
+@example
+@group
+
+typedef struct t_cmbf @{
+ VP exinf; /* extended information */
+ ATR mbfatr; /* message buffer attributes */
+ INT bufsz; /* buffer size (in bytes) */
+ INT maxmsz; /* maximum message size (in bytes) */
+ /* (CPU and/or implementation-dependent information may also be
+ included) */
+@} T_CMBF;
+
+@end group
+@end example
+
+where the meaning of each field is:
+
+@table @b
+@item exinf
+is for any extended information that the implementation may define. This
+implementation does not use this field.
+
+@item mbfatr
+is the attributes for the message buffer. The only attributes which can
+be specified is whether tasks wait in FIFO (@code{TA_TFIFO}) or priority
+(@code{TA_TPRI}) order.
+
+@item bufsz
+is the size of the message buffer. Since some control data are needed to
+manage each messages in the message buffer, @code{bufsz} is usually
+larger than the total of all message sizes in this buffer.
+
+@item maxmsz
+is the maximum message size.
+
+@end table
+
+@subsection T_RMBF Structure
+
+The T_RMBF structure is filled in by the @code{ref_mbf} routine with
+status and state information of the message buffer. The structure is
+defined as follows:
+
+@example
+@group
+
+typedef struct t_rmbf @{
+ VP exinf; /* extended information */
+ BOOL_ID wtsk; /* waiting task information */
+ BOOL_ID stsk; /* sending task information */
+ INT msgsz; /* message size (in bytes) */
+ INT frbufsz; /* free buffer size (in bytes) */
+ /* (CPU and/or implementation-dependent information is returned) */
+@} T_RMBF;
+
+@end group
+@end example
+
+@table @b
+
+@item exinf
+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 tasks waiting on this message buffer
+to send message. It is FALSE when there is no waiting task. 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 stsk
+is TRUE when there is one or more tasks waiting on this message buffer
+to receive message. It is FALSE when there is no waiting task. 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 msgsz
+is the size of the message that is at the head of the message buffer. If
+there is no message on the message queue, @code{msgsz} will be returned
+as FALSE = 0.
+
+@item frbufsz
+is the amount of free memory in the message buffer.
+
+@end table
+
@section Operations
@section System Calls
@@ -38,7 +133,6 @@ A subsection is dedicated to each of this manager's services
and describes the calling sequence, related constants, usage,
and status codes.
-
@c
@c cre_mbf
@c
@@ -62,12 +156,55 @@ ER cre_mbf(
@subheading STATUS CODES:
-@code{EXXX} -
+@code{E_OK} - Normal Completion
+
+@code{E_NOMEM} - Insufficient memory (Memory for control block and/or
+ring buffer cannot be allocted)
+
+@code{E_ID} - Invalid ID number (mbfid was invalid or could not be used)
+
+@code{E_RSATR} - Reserved attribute (mbfatr was invalid or could not be
+used)
+
+@code{E_OBJ} - Invalid object state (a messagebuffer of the same ID
+already exists)
+
+@code{E_OACV} - Object access violation (A mbfid less than -4 was
+specified from a user task. This is implementation dependent.)
+
+@code{E_PAR} - Parameter error (pk_cmbf is invalid or bufsz and/or
+maxmsz is negative or invalid)
+
+@code{EN_OBJNO} - An object number which could not be accessed on the
+target node is specified.
+
+
+@code{EN_CTXID} - Specified an object on another node when the system
+call was issued from a task in dispatch disabled state or from a
+task-independent portion
+
+@code{EN_PAR} - A value outside the range supported by the target node
+and/or transmission packet format was specified as a parameter (a value
+outside supported range was specified for exinf, mbfatr, bufsz and/or
+maxmsz)
@subheading DESCRIPTION:
+This routine creates a message buffer on the local node. The message
+buffer is initialized based on the attributes specified in the
+@code{pk_cmbf} structure. The buffer size and the maximum message size
+are determined by the @code{bufsz} and @code{maxmsz} fields in this
+structure.
+
+The @code{mbfatr} field represents attributes of the message
+buffer. If @code{TA_TFIFO} is specified, tasks will be put on the queue
+on a First In-First Out basis. If @code{TA_TPRI} is specified, tasks
+will be placed on the queue according to their priority.
+
@subheading NOTES:
+Multiprocessing is not supported. Thus none of the "EN_" status codes
+will be returned.
@c
@c del_mbf
@@ -91,19 +228,46 @@ ER del_mbf(
@subheading STATUS CODES:
-@code{EXXX} -
+@code{E_OK} - Normal Completion
+
+@code{E_ID} - Invalid ID number (mbfid was invalid or could not be used)
+
+@code{E_NOEXS} - Object does not exist (the messagebuffer specified by
+mbfid does not exist)
+
+@code{E_OACV} - Object access violation (A mbfid less than -4 was
+specified from a user task. This is implementation dependent.)
+
+@code{EN_OBJNO} - An object number which could not be accessed on the
+target node is specified.
+
+@code{EN_CTXID} - Specified an object on another node when the system
+call was issued from a task in dispatch disabled state or from a
+task-independent portion
@subheading DESCRIPTION:
+This routine deletes the message buffer specified by @code{mbfid}.
+Issuing this system call releases memory area used for the control block of
+the associated message buffer and the buffer area used for storing messages.
+
+This routine will complete normally even if there are tasks waiting to
+send or receive messages at the message buffer. In that case, an
+@code{E_DLT} error will be returned to each waiting task. If there are
+messages still in the message buffer, they will be deleted along with
+the message buffer and no error will result.
+
@subheading NOTES:
+Multiprocessing is not supported. Thus none of the "EN_" status codes
+will be returned.
@c
@c snd_mbf
@c
@page
-@subsection snd_mbf - Send Message to MessageBuffer
+@subsection snd_mbf - Send Message to Message Buffer
@subheading CALLING SEQUENCE:
@@ -122,19 +286,63 @@ ER snd_mbf(
@subheading STATUS CODES:
-@code{EXXX} -
+@code{E_OK} - Normal Completion
+
+@code{E_ID} - Invalid ID number (mbfid was invalid or could not be used)
+
+@code{E_NOEXS} - Object does not exist (the message buffer specified by
+mbfid does not exist)
+
+@code{E_OACV} - Object access violation (A mbfid less than -4 was
+specified from a user task. This is implementation dependent.)
+
+@code{E_PAR} - Parameter error (msgsz is 0 or less; msgsz is larger than
+maxmsz; values unsuitable for msg; tmout is -2 or less)
+
+@code{E_DLT} - The object being waited for was deleted (the
+message buffer of interest was deleted while waiting)
+
+@code{E_RLWAI} - WAIT state was forcibly released (rel_wai was received
+while waiting)
+
+@code{E_CTX} - Context error (issued from task-independent portions or a
+task in dispatch disabled state; implementation dependent for psnd_mbf
+and tsnd_mbf(tmout=TMO_POL))
+
+@code{EN_OBJNO} - An object number which could not be accessed on the
+target node is specified.
+
+@code{EN_CTXID} - Specified an object on another node when the system
+call was issued from a task in dispatch disabled state or from a
+task-independent portion (implementation-dependent; applicable to
+psnd_mbf and tsnd_mbf (tmout=TMO_POL) only)
+
+@code{EN_PAR} - A value outside the range supported by the target node
+and/or transmission packet format was specified as a parameter (a value
+outside supported range was specified for msgsz and/or tmout)
@subheading DESCRIPTION:
+This routine sends the message stored at the address given by @code{msg}
+to the message buffer specified by @code{mbfid}. The size of the
+message is specified by @code{msgsz}; that is, @code{msgsz} number of
+bytes beginning from @code{msg} are copied to the message buffer
+specified by @code{mbfid}. If the available space in the buffer is not
+enough to include the message given by @code{msg}, the task issuing this
+system call will wait on a send wait queue until more buffer space
+becomes available.
+
@subheading NOTES:
+Multiprocessing is not supported. Thus none of the "EN_" status codes
+will be returned.
@c
@c psnd_mbf
@c
@page
-@subsection psnd_mbf - Poll and Send Message to MessageBuffer
+@subsection psnd_mbf - Poll and Send Message to Message Buffer
@subheading CALLING SEQUENCE:
@@ -153,19 +361,71 @@ ER ercd =psnd_mbf(
@subheading STATUS CODES:
-@code{EXXX} -
+@code{E_OK} - Normal Completion
+
+@code{E_ID} - Invalid ID number (mbfid was invalid or could not be used)
+
+@code{E_NOEXS} - Object does not exist (the message buffer specified by
+mbfid does not exist)
+
+@code{E_OACV} - Object access violation (A mbfid less than -4 was
+specified from a user task. This is implementation dependent.)
+
+@code{E_PAR} - Parameter error (msgsz is 0 or less; msgsz is larger than
+maxmsz; values unsuitable for msg; tmout is -2 or less)
+
+@code{E_DLT} - The object being waited for was deleted (the
+message buffer of interest 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
+
+@code{E_CTX} - Context error (issued from task-independent portions or a
+task in dispatch disabled state; implementation dependent for psnd_mbf
+and tsnd_mbf(tmout=TMO_POL))
+
+@code{EN_OBJNO} - An object number which could not be accessed on the
+target node is specified.
+
+@code{EN_CTXID} - Specified an object on another node when the system
+call was issued from a task in dispatch disabled state or from a
+task-independent portion (implementation-dependent; applicable to
+psnd_mbf and tsnd_mbf (tmout=TMO_POL) only)
+
+@code{EN_PAR} - A value outside the range supported by the target node
+and/or transmission packet format was specified as a parameter (a value
+outside supported range was specified for msgsz and/or tmout)
@subheading DESCRIPTION:
+This routine has the same function as @code{snd_mbf} except for the
+waiting feature. @code{Psnd_mbf} polls whether or not the task should
+wait if @code{snd_mbf} is executed. The meaning of parameters to
+@code{psnd_mbf} are the same as for @code{snd_mbf}. The specific
+operations by @code{psnd_mbf} are as follows.
+
+ - If there is enough space in the buffer, processing is the same as
+ @code{snd_mbf}: the message is sent and the system call completes
+ normally.
+
+ - If there is not enough space in the buffer, an @code{E_TMOUT} error
+ is returned to indicate polling failed and the system call finishes.
+ Unlike @code{snd_mbf}, the issuing task does not wait in this case.
+ The status of the message buffer and the message queue remain unchanged.
+
@subheading NOTES:
+Multiprocessing is not supported. Thus none of the "EN_" status codes
+will be returned.
@c
@c tsnd_mbf
@c
@page
-@subsection tsnd_mbf - Send Message to MessageBuffer with Timeout
+@subsection tsnd_mbf - Send Message to Message Buffer with Timeout
@subheading CALLING SEQUENCE:
@@ -185,19 +445,72 @@ ER ercd =tsnd_mbf(
@subheading STATUS CODES:
-@code{EXXX} -
+@code{E_OK} - Normal Completion
+
+@code{E_ID} - Invalid ID number (mbfid was invalid or could not be used)
+
+@code{E_NOEXS} - Object does not exist (the message buffer specified by
+mbfid does not exist)
+
+@code{E_OACV} - Object access violation (A mbfid less than -4 was
+specified from a user task. This is implementation dependent.)
+
+@code{E_PAR} - Parameter error (msgsz is 0 or less; msgsz is larger than
+maxmsz; values unsuitable for msg; tmout is -2 or less)
+
+@code{E_DLT} - The object being waited for was deleted (the
+message buffer of interest 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
+
+@code{E_CTX} - Context error (issued from task-independent portions or a
+task in dispatch disabled state; implementation dependent for psnd_mbf
+and tsnd_mbf(tmout=TMO_POL))
+
+@code{EN_OBJNO} - An object number which could not be accessed on the
+target node is specified.
+
+@code{EN_CTXID} - Specified an object on another node when the system
+call was issued from a task in dispatch disabled state or from a
+task-independent portion (implementation-dependent; applicable to
+psnd_mbf and tsnd_mbf (tmout=TMO_POL) only)
+
+@code{EN_PAR} - A value outside the range supported by the target node
+and/or transmission packet format was specified as a parameter (a value
+outside supported range was specified for msgsz and/or tmout)
@subheading DESCRIPTION:
+The @code{tsnd_mbf} system call has the same function as @code{snd_mbf}
+with an additional timeout feature. A maximum wait time (timeout value)
+can be specified using the parameter @code{tmout}. When a timeout is
+specified, a timeout error, @code{E_TMOUT}, will result and the system
+call will finish if the period specified by @code{tmout} elapses without
+conditions for releasing wait being satisfied (i.e. without sufficient
+buffer space becoming available).
+
+Only positive values can be specified for @code{tmout}. Specifying
+@code{TMO_POL} = 0 to @code{tsnd_mbf} for @code{tmout} indicates that a
+timeout value of 0 be used, resulting in exactly the same processing as
+@code{psnd_mbf}. Specifying @code{TMO_FEVR} = -1 to @code{tsnd_mbf} for
+@code{tmout} indicates that an infinite timeout value be used, resulting
+in exactly the same processing as @code{snd_mbf}.
+
@subheading NOTES:
+Multiprocessing is not supported. Thus none of the "EN_" status codes
+will be returned.
+
@c
@c rcv_mbf
@c
@page
-@subsection rcv_mbf - Receive Message from MessageBuffer
+@subsection rcv_mbf - Receive Message from Message Buffer
@subheading CALLING SEQUENCE:
@@ -216,19 +529,61 @@ ER rcv_mbf(
@subheading STATUS CODES:
-@code{EXXX} -
+@code{E_OK} - Normal Completion
+
+@code{E_ID} - Invalid ID number (mbfid was invalid or could not be used)
+
+@code{E_NOEXS} - Object does not exist (the message buffer specified by
+mbfid does not exist)
+
+@code{E_OACV} - Object access violation (A mbfid less than -4 was
+specified from a user task. This is implementation dependent.)
+
+@code{E_PAR} - Parameter error (values unsuitable for msg; tmout is -2
+or less)
+
+@code{E_DLT} - The object being waited for was deleted (the specified
+message buffer was deleted while waiting)
+
+@code{E_RLWAI} - WAIT state was forcibly released (rel_wai was received
+while waiting)
+
+@code{E_CTX} - Context error (issued from task-independent portions or a
+task in dispatch disabled state)
+
+@code{EN_OBJNO} - An object number which could not be accessed on the
+target node is specified.
+
+@code{EN_PAR} - A value outside the range supported by the target node
+and/or transmission packet format was specified as a parameter (a value
+outside supported range was specified for tmout)
+
+@code{EN_RPAR} - A value outside the range supported by the issuing node
+and/or transmission packet format was returned as a return parameter (msgsz is outside supported range for requesting node)
@subheading DESCRIPTION:
+@code{Rcv_mbf} receives the message from the message buffer specified by
+@code{mbfid}, and stores it at the memory location given by @code{msg}.
+In other words, the content of the message at the head of the message
+buffer specified by @code{mbfid} is copied into an area which begins
+from @code{msg} and whose size is @code{msgsz}.
+
+If the message buffer is empty, the task issuing this system call will wait
+on a receive message wait queue until a message arrives.
+
@subheading NOTES:
+Multiprocessing is not supported. Thus none of the "EN_" status codes
+will be returned.
+
@c
@c prcv_mbf
@c
@page
-@subsection prcv_mbf - Poll and Receive Message from MessageBuffer
+@subsection prcv_mbf - Poll and Receive Message from Message Buffer
@subheading CALLING SEQUENCE:
@@ -247,19 +602,69 @@ ER ercd =prcv_mbf(
@subheading STATUS CODES:
-@code{EXXX} -
+@code{E_OK} - Normal Completion
+
+@code{E_ID} - Invalid ID number (mbfid was invalid or could not be used)
+
+@code{E_NOEXS} - Object does not exist (the message buffer specified by
+mbfid does not exist)
+
+@code{E_OACV} - Object access violation (A mbfid less than -4 was
+specified from a user task. This is implementation dependent.)
+
+@code{E_PAR} - Parameter error (values unsuitable for msg; tmout is -2
+or less)
+
+@code{E_DLT} - The object being waited for was deleted (the specified
+message buffer 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
+
+@code{E_CTX} - Context error (issued from task-independent portions or a
+task in dispatch disabled state)
+
+@code{EN_OBJNO} - An object number which could not be accessed on the
+target node is specified.
+
+@code{EN_PAR} - A value outside the range supported by the target node
+and/or transmission packet format was specified as a parameter (a value
+outside supported range was specified for tmout)
+
+@code{EN_RPAR} - A value outside the range supported by the issuing node
+and/or transmission packet format was returned as a return parameter (msgsz is outside supported range for requesting node)
+
@subheading DESCRIPTION:
+The @code{prcv_mbf} system call has the same function as @code{rcv_mbf}
+except for the waiting feature. @code{Prcv_mbf} polls whether or not
+the task should wait if @code{rcv_mbf} is executed. The meaning of
+parameters to @code{prcv_mbf} are the same as for @code{rcv_mbf}. The
+specific operations by @code{prcv_mbf} are as follows.
+
+ - If there is a message in the specified message buffer, processing is
+the same as @code{rcv_mbf}: the first message on the message buffer is
+retrieved and the system call completes normally.
+
+ - If there is no message in the specified message buffer, an
+@code{E_TMOUT} error is returned to indicate polling failed and the
+system call finishes. Unlike @code{rcv_mbf}, the issuing task does not
+wait in this case. The status of the message buffer remain unchanged.
@subheading NOTES:
+Multiprocessing is not supported. Thus none of the "EN_" status codes
+will be returned.
+
@c
@c trcv_mbf
@c
@page
-@subsection trcv_mbf - Receive Message from MessageBuffer with Timeout
+@subsection trcv_mbf - Receive Message from Message Buffer with Timeout
@subheading CALLING SEQUENCE:
@@ -279,19 +684,67 @@ ER ercd =trcv_mbf(
@subheading STATUS CODES:
-@code{EXXX} -
+@code{E_OK} - Normal Completion
+
+@code{E_ID} - Invalid ID number (mbfid was invalid or could not be used)
+
+@code{E_NOEXS} - Object does not exist (the message buffer specified by
+mbfid does not exist)
+
+@code{E_OACV} - Object access violation (A mbfid less than -4 was
+specified from a user task. This is implementation dependent.)
+
+@code{E_PAR} - Parameter error (values unsuitable for msg; tmout is -2
+or less)
+
+@code{E_DLT} - The object being waited for was deleted (the specified
+message buffer 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
+
+@code{E_CTX} - Context error (issued from task-independent portions or a
+task in dispatch disabled state)
+
+@code{EN_OBJNO} - An object number which could not be accessed on the
+target node is specified.
+
+@code{EN_PAR} - A value outside the range supported by the target node
+and/or transmission packet format was specified as a parameter (a value
+outside supported range was specified for tmout)
+
+@code{EN_RPAR} - A value outside the range supported by the issuing node
+and/or transmission packet format was returned as a return parameter (msgsz is outside supported range for requesting node)
@subheading DESCRIPTION:
+The @code{trcv_mbf} system call has the same function as @code{rcv_mbf}
+with an additional timeout feature. A maximum wait time (timeout value)
+can be specified using the parameter @code{tmout}. When a timeout is
+specified, a timeout error, @code{E_TMOUT}, will result and the system
+call will finish if the period specified by @code{tmout} elapses without
+conditions for releasing wait being satisfied (i.e. without a message
+arriving).
+
+Only positive values can be specified for @code{tmout}. Specifying
+@code{TMO_POL} = 0 to @code{trcv_mbf} for @code{tmout} indicates that a
+timeout value of 0 be used, resulting in exactly the same processing as
+@code{prcv_mbf}. Specifying @code{TMO_FEVR} = -1 to @code{trcv_mbf} for
+tmout indicates that an infinite timeout value be used, resulting in
+exactly the same processing as @code{rcv_mbf}.
@subheading NOTES:
+Multiprocessing is not supported. Thus none of the "EN_" status codes
+will be returned.
@c
@c ref_mbf
@c
@page
-@subsection ref_mbf - Reference MessageBuffer Status
+@subsection ref_mbf - Reference Message Buffer Status
@subheading CALLING SEQUENCE:
@@ -309,9 +762,61 @@ ER ref_mbf(
@subheading STATUS CODES:
-@code{EXXX} -
+@code{E_OK} - Normal Completion
+
+@code{E_ID} - Invalid ID number (mbfid was invalid or could not be used)
+
+@code{E_NOEXS} - Object does not exist (the message buffer specified by
+mbfid does not exist)
+
+@code{E_OACV} - Object access violation (A mbfid less than -4 was
+specified from a user task. This is implementation dependent.)
+
+@code{E_PAR} - Parameter error (the packet address for the return
+parameters could not be used)
+
+@code{EN_OBJNO} - An object number which could not be accessed on the
+target node is specified.
+
+@code{EN_CTXID} - Specified an object on another node when the system
+call was issued from a task in dispatch disabled state or from a
+task-independent portion
+
+@code{EN_RPAR} - A value outside the range supported by the issuing node
+and/or transmission packet format was returned as a return parameter (a
+value outside supported range for exinf, wtsk, stsk, msgsz and/or
+frbufsz on a requesting node)
@subheading DESCRIPTION:
+This system call refers to the state of the message buffer specified by
+@code{mbfid}, and returns information of a task waiting to send a
+message (@code{stsk}), the size of the next message to be received
+(@code{msgsz}), the free buffer size (@code{frbufsz}), information of a
+task waiting to receive a message (@code{wtsk}), and its extended
+information (@code{exinf}).
+
+@code{Wtsk} and @code{stsk} indicate whether or not there is a task
+waiting for the message buffer in question. If there is no waiting
+task, @code{wtsk} and @code{stsk} are returned as @code{FALSE} = 0. If
+there is a waiting task, @code{wtsk} and @code{stsk} are returned as
+values other than 0.
+
+An @code{E_NOEXS} error will result if the message buffer specified to
+@code{ref_mbf} does not exist.
+
+The size of the message at the head of the message buffer (the next
+message to be received) is returned to @code{msgsz}. If there are no
+messages on the message buffer, @code{msgsz} will be returned as
+@code{FALSE} = 0. A message whose size is zero cannot be sent.
+
+At least one of @code{msgsz} = @code{FALSE} and @code{wtsk} =
+@code{FALSE} is always true in this system call.
+
+@code{Frbufsz} indicates the amount of free memory in the message
+buffer. This value can be used to know the total approximate size of
+the messages which can be sent to the message buffer.
@subheading NOTES:
+Multiprocessing is not supported. Thus none of the "EN_" status codes
+will be returned.