UM0851 datasheet(159/245 Pages) STMICROELECTRONICS

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UM0851

Accelerator engine device drivers

Doc ID 16604 Rev 2

159/245

size: variable which will store size of output data in bytes. This must always be

equal to size of individual read buffer. If it is less than size of individual read

buffer, end of encoding/decoding is indicated.

This is a blocking system call which unblocks or returns only when the output data size less

than equal to the size of the individual read buffer is written to current read buffer after

encoding/decoding. On success, zero is returned otherwise, -1 is returned on error and

errno is set appropriately. For example: total size of output data is 15 K, size of each write

buffer is 4 K, then user needs to do following steps to read data from JPEG:

Set current read buffer to read_buffer0

Call JPEGIOC_GET_OUT_DATA_SIZE ioctl

Check value of parameter size, if it is less than 4 K end of encoding/decoding is

indicated

Read data from current read buffer

Toggle current read buffer to buffer1 if current buffer is buffer0, else to buffer0 if current

buffer is buffer1

Follow steps 2, 3, 4, 5 till the time step 3 doesn't indicate end of encoding/decoding.

Writing input data to write buffer and reading output data from read buffer have to be done

simultaneously. It is recommended to use different threads/processes for reading and

writing. This will speed up encoding/decoding process.

Get JPEG information

Once encoding/decoding is finished user can read JPEG information (JPEG header

information and compression tables). Use the following system call to get JPEG information:

ioctl(rfd, JPEGIOC_GET_INFO, &jpeg_info);

rfd: read node file descriptor.

JPEGIOC_GET_INFO: command to get jpeg information.

jepg_info: instance of struct jpeg_info. After successful completion of this system

call, it will contain information of JPEG header and compression tables.

On success, zero is returned otherwise, -1 is returned on error and errno is set

appropriately.

struct jpeg_hdr_info is defined below:

struct jpeg_info {

struct jpeg_hdr hdr;/* jpeg image header */

char qnt_mem[QNT_MEM_SIZE]; /* quantization memory */

char hmin_mem[HMIN_MEM_SIZE]; /* Huff min memory */

char hbase_mem[HBASE_MEM_SIZE]; /* Huff base memory */

char hsymb_mem[HSYMB_MEM_SIZE]; /* Huff symb memory */

char dht_mem[DHT_MEM_SIZE]; /* DHT memory */

char henc_mem[HENC_MEM_SIZE]; /* Huff enc memory */

};

struct jpeg_hdr is already defined earlier in section "Set JPEG Info".

This ioctl is mainly useful for DWH (decoding with header processing enabled).

Munmap

Once the application is finished with JPEG processing, it should unmap the memory that

has been mapped for read and write buffers. Use the following system call to unmap

memory:

UM0851 Datasheet(PDF) 159 Page - STMicroelectronics

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