UM0851 datasheet(155/245 Pages) STMICROELECTRONICS

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UM0851

Accelerator engine device drivers

Doc ID 16604 Rev 2

155/245

29 fb

89 i2c

90 mtd

128 ptm

136 pts

180 usb

189 usb_device

206 osst

250 usb_endpoint

251 C3

252 spear-jpeg

254 rtc

Block devices:

1 ramdisk

31 mtdblock

After obtaining the major number of the JPEG device, create JPEG nodes using the

following commands:

mknod /dev/jpegread c major 0

mknod /dev/jpegwrite c major 1

Here,

major: is major number allocated to JPEG

These user level nodes are used for any further interaction with the JPEG driver. The

following steps illustrate how to do encoding/decoding with JPEG.

Open JPEG nodes

After creating JPEG read and write nodes, the application should open them. Use the

following system call to open JPEG nodes:

rfd = open("/dev/jpegread", O_RDWR | O_SYNC);

wfd = open("/dev/jpegwrite", O_RDWR | O_SYNC);

O_RDWR access permission is used to get read/write permissions.

O_SYNC access permission is used for synchronous I/O. Any writes on the resulting

file descriptor will block the calling process until the data has been physically

written to the underlying hardware. MMap function used later will give uncached

memory if this flag is used, otherwise data consistency issues will occur.

Rfd & wfd: are read and write file descriptors used to further communicate with jpeg

nodes.

JPEG nodes can be opened by only one application at a time, thus it can’t be shared. On

success, positive file descriptors are returned, otherwise on error, -1 is returned and errno is

set appropriately. These file descriptors can be used for any further communication with the

JPEG device.

Set source image size

The JPEG driver must be told in advance the size of the input data (required by hardware).

Use the following system call to set the input data size:

ioctl(wfd, JPEGIOC_SET_SRC_IMG_SIZE, size);

wfd: file descriptor of jpeg write node.

JPEGIOC_SET_SRC_IMG_SIZE: ioctl command for setting input data size.

size: size of source image in bytes.

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