Texas Instruments OMAP35 Series User Manual page 99

6.2.2.3. Buffer Management
Table 6.2. Memory requirement for V4L2 and FBDEV driver Buffers
V4L2 Driver
Memory Mapped buffer mode and User pointer buffer mode are the two memory
allocation modes supported by driver.
In Memory map buffer mode, application can request memory from the driver
by calling VIDIOC_REQBUFS ioctl. In this mode, maximum number of buffers is
limited to VIDEO_MAX_FRAME (defined in driver header files) and is limited by
the available memory in the kernel. If driver is not able to allocate the requested
number of buffer, it will return the number of buffer it is able to allocate. The
main steps that the application must perform for buffer allocation are:
1) Allocating Memory
This ioctl is used to allocate memory for frame buffers. This is a necessary ioctl
for streaming IO. It has to be called for both drivers buffer mode and user buffer
mode. Using this ioctl, driver will identify whether driver buffer mode or user
buffer mode will be used.
Ioctl: VIDIOC_REQBUFS
It takes a pointer to instance of the v4l2_requestbuffers structure as an
argument.
User can specify the buffer type (V4L2_BUF_TYPE_VIDEO_OUTPUT), number of
buffers, and memory type (V4L2_MEMORY_MMAP, V4L2_MEMORY_USERPTR)at the
time of buffer allocation. In case of driver buffer mode, this ioctl also returns the
actual number of buffers allocated in count member of v4l2_requestbuffer
structure
It can be called with zero number of buffers to free up all the buffers already
allocated. It also frees allocated buffers when application changes buffer
Version 02.01.01.08
Driver Without Rotation
FBDEV Driver A single
1280*720*4*2 bytes
V4L2 Driver Single
1280*720*4 bytes. Number
of buffers can be configures
using
ioctl and
argument.
Platform Support Products
With Rotation
buffer of size A
2048*720*4 bytes
buffer takes Same
without
Additionally allocates one
VIDIOC_REQBUFS buffer of size 1695744 bytes
command line for each context. Number
of context are same as the
number of buffers allocated
using REQBUFS not more
than four.
Display Driver
single buffer of size
requirement
rotation.
Usage
as
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