Cypress DCT-1D Betriebsanweisung PDF herunterladen (Seite 67)

6.5. SOFTWARE IMPLEMENTATION

6.5.2 Integration into jpegﬁles

When you ﬁnd that the hardware is working and you have written some test programs

to verify that the the processor can execute your instruction. You are ready for the

next step, to get the instruction to work for you in jpegﬁles. You need to add code

for three phases of operation, as described below. The only ﬁle you need to modify is

jchuff.c, look for the

#ifdef HW_INST

blocks.

Phase 1: VLX Initialization

This, the ﬁrst, phase is executed before processing of the bit stream starts . In this phase

you must ensure that your hardware is properly initialized. It is important to set the

address where your hardware shall star t writing the bit stream to memor y.

Phase 2: VLX Operation

This, the second, phase is executed as long as there is new data to encode. This phase

is rather simple, just use your hardware to write the incoming bit stream to memory.

Phase 3: VLX Finalization

This, the thir d and ﬁnal, phase is executed when there are no more data to encode. In

this phase you must ensure that data not yet written to memory, still residing in your

hardware, is correctly put in the memory. Also you must ensure that you make a clean

hand off to jpegﬁles so it can take care of some ﬁnalization operations, like writing

the JPEG end marker. Take note of the

next_buffer

variable and think about what you

have to do with it.

6.5.3 JPEG Markers

There are a number of bit strings called markers in the JFIF binary ﬁle. A marker is

always byte aligned and s tarts with the byte 0xF F , the next byte speciﬁes what marker

it is. For this reason if 0xF F is encountered in the scan data, 0xF F must be written

as 0xF F 00. Some markers are stand alone markers, meaning that the marker has no

additional information associated with it. Otherwise the marker has a two byte code

immediately following the marker specifying the length in byte of extra data associated

with the marker. A marker followed by data is referred to as a marker segment. Table

6.3 list a few important markers, see [17] for more information about markers and [18]

for some speciﬁc restriction of markers in J FIF.

Laboration task 13

Implement the new instruction in hardware and show that you can use the new instruc-

tion using inline assembler in C-code.

Laboration task 14

Modify the jpegﬁles code to use your new instruction.

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Cypress DCT-1D Betriebsanweisung Seite 67