Atmel Evaluation Kit AT91SAM9M10-G45-EK AT91SAM9M10-G45-EK Hoja De Datos
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AT91SAM9M10-G45-EK
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SAM9M10 [DATASHEET]
6355F–ATARM–12-Mar-13
Figure 46-2.
Multi-format Decoder and External Memory Data Flow in VLC Mode
46.3.3
Decoder Data Flow, Software Performs Entropy Decoding (RLC Mode)
In this case, the decoder software starts decoding the first picture by parsing the stream headers (
1
), and by per-
forming entropy decoding. Software then writes the following items to external memory:
• Run-length-coded (RLC) data (
2
)
• Differential motion vectors (
3
)
• Intra 4x4 prediction modes (in H.264) or separate DC coefficients (in MPEG-4, if the stream is using data
partitioning) (
4
)
• Macroblock control data (
5
)
Last step for the software is to write the hardware control registers and to enable the hardware (
6
).
Hardware decodes the picture by buffering control data for several macroblocks at a time, and then reads appropri-
ate amount of RLC data, differential motion vectors and intra modes depending on each macroblock type (
ate amount of RLC data, differential motion vectors and intra modes depending on each macroblock type (
7
)
–
(
10
).
Hardware will also read the reference pictures (previously decoded pictures) as required (
11
). Hardware writes
decoded (in-loop filtered, if H.264) output picture to memory one macroblock at a time (
12
). When the picture has
been fully decoded, hardware gives an interrupt and returns to initial state.
If post-processing is enabled, one or two additional image transfer operations will take place. If the decoded
images are in display order (i.e. no picture re-ordering has been made when encoding the sequence), and rotation
is not used, PP will process the pictures in pipeline with the decoder. Otherwise, it will first have to read the
decoded image that is to be displayed next from the memory (
images are in display order (i.e. no picture re-ordering has been made when encoding the sequence), and rotation
is not used, PP will process the pictures in pipeline with the decoder. Otherwise, it will first have to read the
decoded image that is to be displayed next from the memory (
13
), and then write back the processed image (
14
).
H.264 NAL
Unit Stream
ARM Processor Core
Multiformat HW
Decoder Core
Decoded
Picture Buffer
Post-Processed
Picture Buffer
External Memory
AHB Bus
1
3
4
5
(6)
7
2