dmbuffer(4) dmbuffer(4)
DMbuffer, DMbufferpool - Digital Media data transport subsystem
#include <dmedia/dm_buffer.h>
-ldmedia
DMbufferpool pool;
DMbuffer buf;
The DMbufferpool and DMbuffer data types and operations on them implement
the Digital Media data transport subsystem. This subsystem is for
sharing and exchanging time sensitive visual data between compression
devices and algorithms, video input/output, graphics rendering and
texturing, and the host processor(s).
An overview of the DMbufferpool and DMbuffer data types is presented here
along with brief descriptions of their defined operations within the data
transport subsystem as well as in the image converter subsystem (dmIC),
video I/O subsystem (VL), and graphics (Opengl DMbuffer extension).
Refer to the individual manual pages for detailed descriptions of each
operation.
A DMbufferpool is memory specially allocated to guarantee the
requirements of one or more time sensitive visual data processing and/or
transport devices. Before a process begins operation of one or more such
devices one or more DMbufferpool's are created.
In general a DMbufferpool is quite large and depending on device
requirements may consist of physical memory. Full rate full size video
I/O devices and full rate full size image conversion devices
(compression/decompression) generally require large amounts of physical
memory. For these reasons the initial creation of all DMbufferpool's is
best done during program initialization.
A DMbuffer generally holds a video image (field or frame) or data
representing a compressed video image. The exact description of the data
in the buffer is generally held in a DMparams data structure which the
program manages separately from the DMbuffers. That is, the DMbuffer
subsystem does not itself have any knowledge of the data.
Each DMbuffer is allocated from a DMbufferpool and when no longer needed
is returned to that pool for reuse. A file descriptor for the
DMbufferpool is available for use with select(2) to determine when there
is a DMbuffer available for allocation. The operations to allocate a
DMbuffer and return one for reuse are very lightweight. Multiple
outstanding DMbuffer's are well behaved and may be further transported to
and from video I/O devices, image converter devices and algorithms, and
graphics out of order with respect to allocation.
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dmbuffer(4) dmbuffer(4)
dmBufferCreatePool creates a DMbufferpool using a DMparams
parameter/value list encapsulating the combined buffering requirements of
all devices to access this memory. After a pool is created the host may
initiate device and/or direct access to the memory at the granularity of
a DMbuffer.
dmBufferSetPoolDefaults initializes the DMparams list which can then be
passed to: dmICGetSrcPoolParams or dmICGetDstPoolParams to gather the
input or output memory requirements of an image conversion (compression,
decompression) device or algorithm; vlDMPoolGetParams(3dm) to gather the
memory requirements of a video input or output device.
dmBufferGetPoolFD returns a file descriptor for use in the writefds
fd_set in select(2). When select returns a ready indication for this file
descriptor the process is assured that dmBufferAllocate will successfully
allocate a new DMbuffer.
dmBufferMapData gives the host direct access to the memory in the
DMbuffer.
The DMbuffer may be transferred to and from one or more devices as
described in the next section.
dmBufferFree releases the buffer and further is the only means by which a
process releases a buffer for reuse. A buffer is not available for reuse
until all devices as well as the process release their reference to the
buffer.
A DMbuffer originating in the process is used as follows:
dmBufferAllocate(pool, &buf);
cp = dmBufferMapData(buf);
bcopy(from, cp, nbytes);
-orread(fd,
cp, nbytes);
dmBufferSetSize(buf, nbytes);
(*send1)(handle1, buf);
(*send2)(handle2, buf);
dmBufferFree(buf);
A DMbuffer originating with a device is used as follows:
(*recv)(&buf);
cp = dmBufferMapData(buf);
nbytes = dmBufferGetSize(buf);
bcopy(cp, to, nbytes);
-orwrite(fd,
cp, nbytes);
(*send1)(handle1, buf);
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dmbuffer(4) dmbuffer(4)
(*send2)(handle2, buf);
dmBufferFree(buf);
Note that in either case the DMbuffer is available for further transport
to 0 or more other devices.
The following sections give an overview of the (*send)() and (*recv)()
operations for different classes of visual processing devices.
IMAGE CONVERTER - dmIC
dmICReceive transfers a DMbuffer from the image converter output queue to
the process. This is a simple queue operation and immediately fails if
no data is available. The image converter provides a file descriptor
which indicates when data is available on the output queue.
dmICSend transfers a DMbuffer from the process to the image converter
input queue. This is a simple queue operation and immediately fails if
the input queue is full.
VIDEO DEVICE I/O - VL
vlEventRecv and vlEventToDMBuffer transfer a DMbuffer from a video input
device to the process.
vlDMBufferSend transfers a DMbuffer from the process to a video ouput
device.
dmBufferMapData gives the process a pointer to the data in the DMbuffer.
dmBufferGetSize returns the number of bytes of valid data in the buffer.
dmBufferSetSize is used by the process to set the amount of valid data
placed in the buffer.
dmICGetSrcPoolParams(3dm), dmICGetDstPoolParams(3dm),
vlDMPoolGetParams(3dm), dmBufferCreatePool(3dm), dmBufferAllocate(3dm),
dmICSend(3dm), dmICReceive(3dm), vlEventRecv(3dm),
vlEventToDMBuffer(3dm), vlDMBufferSend(3dm), dmBufferMapData(3dm).
dmbuffer(4) dmbuffer(4)
DMbuffer, DMbufferpool - Digital Media data transport subsystem
#include <dmedia/dm_buffer.h>
-ldmedia
DMbufferpool pool;
DMbuffer buf;
The DMbufferpool and DMbuffer data types and operations on them implement
the Digital Media data transport subsystem. This subsystem is for
sharing and exchanging time sensitive visual data between compression
devices and algorithms, video input/output, graphics rendering and
texturing, and the host processor(s).
An overview of the DMbufferpool and DMbuffer data types is presented here
along with brief descriptions of their defined operations within the data
transport subsystem as well as in the image converter subsystem (dmIC),
video I/O subsystem (VL), and graphics (Opengl DMbuffer extension).
Refer to the individual manual pages for detailed descriptions of each
operation.
A DMbufferpool is memory specially allocated to guarantee the
requirements of one or more time sensitive visual data processing and/or
transport devices. Before a process begins operation of one or more such
devices one or more DMbufferpool's are created.
In general a DMbufferpool is quite large and depending on device
requirements may consist of physical memory. Full rate full size video
I/O devices and full rate full size image conversion devices
(compression/decompression) generally require large amounts of physical
memory. For these reasons the initial creation of all DMbufferpool's is
best done during program initialization.
A DMbuffer generally holds a video image (field or frame) or data
representing a compressed video image. The exact description of the data
in the buffer is generally held in a DMparams data structure which the
program manages separately from the DMbuffers. That is, the DMbuffer
subsystem does not itself have any knowledge of the data.
Each DMbuffer is allocated from a DMbufferpool and when no longer needed
is returned to that pool for reuse. A file descriptor for the
DMbufferpool is available for use with select(2) to determine when there
is a DMbuffer available for allocation. The operations to allocate a
DMbuffer and return one for reuse are very lightweight. Multiple
outstanding DMbuffer's are well behaved and may be further transported to
and from video I/O devices, image converter devices and algorithms, and
graphics out of order with respect to allocation.
Page 1
dmbuffer(4) dmbuffer(4)
dmBufferCreatePool creates a DMbufferpool using a DMparams
parameter/value list encapsulating the combined buffering requirements of
all devices to access this memory. After a pool is created the host may
initiate device and/or direct access to the memory at the granularity of
a DMbuffer.
dmBufferSetPoolDefaults initializes the DMparams list which can then be
passed to: dmICGetSrcPoolParams or dmICGetDstPoolParams to gather the
input or output memory requirements of an image conversion (compression,
decompression) device or algorithm; vlDMPoolGetParams(3dm) to gather the
memory requirements of a video input or output device.
dmBufferGetPoolFD returns a file descriptor for use in the writefds
fd_set in select(2). When select returns a ready indication for this file
descriptor the process is assured that dmBufferAllocate will successfully
allocate a new DMbuffer.
dmBufferMapData gives the host direct access to the memory in the
DMbuffer.
The DMbuffer may be transferred to and from one or more devices as
described in the next section.
dmBufferFree releases the buffer and further is the only means by which a
process releases a buffer for reuse. A buffer is not available for reuse
until all devices as well as the process release their reference to the
buffer.
A DMbuffer originating in the process is used as follows:
dmBufferAllocate(pool, &buf);
cp = dmBufferMapData(buf);
bcopy(from, cp, nbytes);
-orread(fd,
cp, nbytes);
dmBufferSetSize(buf, nbytes);
(*send1)(handle1, buf);
(*send2)(handle2, buf);
dmBufferFree(buf);
A DMbuffer originating with a device is used as follows:
(*recv)(&buf);
cp = dmBufferMapData(buf);
nbytes = dmBufferGetSize(buf);
bcopy(cp, to, nbytes);
-orwrite(fd,
cp, nbytes);
(*send1)(handle1, buf);
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dmbuffer(4) dmbuffer(4)
(*send2)(handle2, buf);
dmBufferFree(buf);
Note that in either case the DMbuffer is available for further transport
to 0 or more other devices.
The following sections give an overview of the (*send)() and (*recv)()
operations for different classes of visual processing devices.
IMAGE CONVERTER - dmIC
dmICReceive transfers a DMbuffer from the image converter output queue to
the process. This is a simple queue operation and immediately fails if
no data is available. The image converter provides a file descriptor
which indicates when data is available on the output queue.
dmICSend transfers a DMbuffer from the process to the image converter
input queue. This is a simple queue operation and immediately fails if
the input queue is full.
VIDEO DEVICE I/O - VL
vlEventRecv and vlEventToDMBuffer transfer a DMbuffer from a video input
device to the process.
vlDMBufferSend transfers a DMbuffer from the process to a video ouput
device.
dmBufferMapData gives the process a pointer to the data in the DMbuffer.
dmBufferGetSize returns the number of bytes of valid data in the buffer.
dmBufferSetSize is used by the process to set the amount of valid data
placed in the buffer.
dmICGetSrcPoolParams(3dm), dmICGetDstPoolParams(3dm),
vlDMPoolGetParams(3dm), dmBufferCreatePool(3dm), dmBufferAllocate(3dm),
dmICSend(3dm), dmICReceive(3dm), vlEventRecv(3dm),
vlEventToDMBuffer(3dm), vlDMBufferSend(3dm), dmBufferMapData(3dm).
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