base/include/rtai_scb.h File Reference

Detailed Description

SCB stand for Shared (memory) Circular Buffer.

It is a non blocking implementation for just a single writer (producer) and reader (consumer) and, under such a constraint, it can be a specific substitute for RTAI mailboxes. There are other constraints that must be satisfied, so it cannot be a general substitute for the more flexible RTAI mailboxes. In fact it provides just functions corresponding to RTAI mailboxes non blocking atomic send/receive of messages, i.e. the equivalents of rt_mbx_send_if and rt_mbx_receive_if. Moreover the circular buffer size must be >= to the largest message to be sent/received. At least the double of the largest message to be sent/received is strongly recommended. Thus sending/receiving a message either succeeds of fails. However thanks to the use of shared memory it should be more efficient than mailboxes in atomic exchanges of messages from kernel to user space. So it is a good candidate for supporting drivers development.

Author:
Paolo Mantegazza
Note:
Copyright © 2004-2008 Paolo Mantegazza <mantegazza@aero.polimi.it>
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

Definition in file rtai_scb.h.

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Defines

#define SCB   ((void *)(scb))
#define SIZE   ((volatile int *)scb)[-3]
#define FBYTE   ((volatile int *)scb)[-2]
#define LBYTE   ((volatile int *)scb)[-1]
#define HDRSIZ   (3*sizeof(int))
#define RTAI_SCB_PROTO   RTAI_PROTO

Functions

 RTAI_SCB_PROTO (void *, rt_scb_init,(unsigned long name, int size, unsigned long suprt))
 Allocate and initialize a shared memory circular buffer.
 RTAI_SCB_PROTO (void, rt_scb_reset,(void *scb))
 Reset a shared memory circular buffer.
 RTAI_SCB_PROTO (int, rt_scb_delete,(unsigned long name))
 Free a shared memory circular buffer.
 RTAI_SCB_PROTO (int, rt_scb_avbs,(void *scb))
 Get the number of bytes avaiable in a shared memory circular buffer.
 RTAI_SCB_PROTO (int, rt_scb_bytes,(void *scb))
 Get the number of bytes avaiable in a shared memory circular buffer.
 RTAI_SCB_PROTO (int, rt_scb_frbs,(void *scb))
 Get the number of free bytes pace in a shared memory circular buffer.
 RTAI_SCB_PROTO (int, rt_scb_get,(void *scb, void *msg, int msg_size))
 Gets (receives) a message, only if the whole message can be passed all at once.
 RTAI_SCB_PROTO (int, rt_scb_evdrp,(void *scb, void *msg, int msg_size))
 eavedrops a message.
 RTAI_SCB_PROTO (int, rt_scb_put,(void *scb, void *msg, int msg_size))
 Puts (sends) a message, only if the whole message can be passed all at once.
 RTAI_SCB_PROTO (int, rt_scb_ovrwr,(void *scb, void *msg, int msg_size))

Define Documentation

#define FBYTE   ((volatile int *)scb)[-2]

Definition at line 48 of file rtai_scb.h.

Referenced by RTAI_SCB_PROTO().

#define HDRSIZ   (3*sizeof(int))

Definition at line 50 of file rtai_scb.h.

Referenced by RTAI_SCB_PROTO().

#define LBYTE   ((volatile int *)scb)[-1]

Definition at line 49 of file rtai_scb.h.

Referenced by RTAI_SCB_PROTO().

#define RTAI_SCB_PROTO   RTAI_PROTO

Definition at line 60 of file rtai_scb.h.

#define SCB   ((void *)(scb))

Definition at line 46 of file rtai_scb.h.

Referenced by RTAI_SCB_PROTO().

#define SIZE   ((volatile int *)scb)[-3]

Definition at line 47 of file rtai_scb.h.

Referenced by RTAI_SCB_PROTO().

Function Documentation

RTAI_SCB_PROTO ( int  ,
rt_scb_ovrwr  ,
(void *scb, void *msg, int msg_size)   
)

Definition at line 314 of file rtai_scb.h.

References LBYTE, SCB, and SIZE.

RTAI_SCB_PROTO ( int  ,
rt_scb_put  ,
(void *scb, void *msg, int msg_size)   
)

Puts (sends) a message, only if the whole message can be passed all at once.

rt_scb_put tries to atomically send the message msg of msg_size bytes to the shared memory circular buffer scb. It returns immediately and the caller is never blocked.

Returns:
On success, i.e. message put, it returns 0, msg_size on failure.

Definition at line 296 of file rtai_scb.h.

References FBYTE, LBYTE, SCB, and SIZE.

RTAI_SCB_PROTO ( int  ,
rt_scb_evdrp  ,
(void *scb, void *msg, int msg_size)   
)

eavedrops a message.

rt_scb_evdrp atomically spies the message msg of msg_size bytes from the shared memory circular buffer scb. It returns immediately and the caller is never blocked. It is like rt_scb_get but leaves the message in the shared memory circular buffer.

Returns:
On success, i.e. message got, it returns 0, msg_size on failure.

Definition at line 268 of file rtai_scb.h.

References FBYTE, LBYTE, SCB, and SIZE.

RTAI_SCB_PROTO ( int  ,
rt_scb_get  ,
(void *scb, void *msg, int msg_size)   
)

Gets (receives) a message, only if the whole message can be passed all at once.

rt_scb_get tries to atomically receive the message msg of msg_size bytes from the shared memory circular buffer scb. It returns immediately and the caller is never blocked.

Returns:
On success, i.e. message got, it returns 0, msg_size on failure.

Definition at line 238 of file rtai_scb.h.

References FBYTE, LBYTE, SCB, and SIZE.

RTAI_SCB_PROTO ( int  ,
rt_scb_frbs  ,
(void *scb)   
)

Get the number of free bytes pace in a shared memory circular buffer.

For internal use only.

rt_scb_frbs is used to get the number of free bytes space avaiable in a shared memory circular buffer.

Parameters:
scb is the pointer handle returned when the buffer was initted.
Returns:
the number of free bytes.

Definition at line 220 of file rtai_scb.h.

References FBYTE, LBYTE, and SIZE.

RTAI_SCB_PROTO ( int  ,
rt_scb_bytes  ,
(void *scb)   
)

Get the number of bytes avaiable in a shared memory circular buffer.

For internal use only.

rt_scb_bytes is used to get the number of bytes avaiable in a shared memory circular buffer; legacy alias for rt_scb_avbs.

Parameters:
scb is the pointer handle returned when the buffer was initted.
Returns:
the available number of bytes.

Definition at line 201 of file rtai_scb.h.

RTAI_SCB_PROTO ( int  ,
rt_scb_avbs  ,
(void *scb)   
)

Get the number of bytes avaiable in a shared memory circular buffer.

For internal use only.

rt_scb_avbs is used to get the number of bytes avaiable in a shared memory circular buffer.

Parameters:
scb is the pointer handle returned when the buffer was initted.
Returns:
the available number of bytes.

Definition at line 181 of file rtai_scb.h.

References FBYTE, LBYTE, and SIZE.

RTAI_SCB_PROTO ( int  ,
rt_scb_delete  ,
(unsigned long name)   
)

Free a shared memory circular buffer.

For internal use only.

rt_scb_delete is used to release a previously allocated shared memory circular buffer.

Parameters:
name is the unsigned long identifier used when the buffer was allocated;
Analogously to what done by all the named allocation functions the freeing calls have just the effect of decrementing a usage count, unmapping any user space shared memory being freed, till the last is done, as that is the one the really frees any allocated memory.

Returns:
the size of the succesfully freed buffer, 0 on failure.
No need to call this function if you provided your own memory for the circular buffer.

Definition at line 162 of file rtai_scb.h.

References rt_shm_free().

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RTAI_SCB_PROTO ( void  ,
rt_scb_reset  ,
(void *scb)   
)

Reset a shared memory circular buffer.

For internal use only.

rt_scb_reset reinitializes a shared memory circular buffer.

Parameters:
scb is the pointer returned when the buffer was initted.

Definition at line 134 of file rtai_scb.h.

References FBYTE, and LBYTE.

RTAI_SCB_PROTO ( void *  ,
rt_scb_init  ,
(unsigned long name, int size, unsigned long suprt)   
)

Allocate and initialize a shared memory circular buffer.

For internal use only.

rt_scb_init is used to allocate and/or initialize a shared memory circular buffer.

Parameters:
name is an unsigned long identifier;
size is the size of the circular buffer.
suprt is the kernel allocation method to be used, it can be:
  • USE_VMALLOC, use vmalloc;
  • USE_GFP_KERNEL, use kmalloc with GFP_KERNEL;
  • USE_GFP_ATOMIC, use kmalloc with GFP_ATOMIC;
  • USE_GFP_DMA, use kmalloc with GFP_DMA.
  • for use in kernel/(multi-threaded)user space only applications the user can use "suprt" to pass the address of any memory area (s)he has allocated on her/his own. In such a case the actual buffer should be greater than the requested size by the amount HDRSIZ at least.
Since an unsigned long can be a clumsy identifier, services are provided to convert 6 characters identifiers to unsigned long, and vice versa.

See also:
nam2num() and num2nam().
It must be remarked that only the very first call does a real allocation, any following call to allocate with the same name, from anywhere, will just increase the usage count and map the circular buffer to the user space, or return the related pointer to the already allocated buffer in kernel/user space. In any case the functions return a pointer to the circular buffer, appropriately mapped to the memory space in use. So if one is really sure that the named circular buffer has been initted already parameters "size" and "suprt" are not used and can be assigned any value.

Returns:
a valid address on succes, you must use it, 0 on failure.

Definition at line 105 of file rtai_scb.h.

References atomic_cmpxchg(), HDRSIZ, and rt_shm_alloc.

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