Cypress DCT-1D Betriebsanweisung PDF herunterladen (Seite 62)

CHAPTER 6. LAB TASK 4 - CUSTOM INSTRUCTIONS

suggests four Huffman tables. Two for the luminance, one for the DC values and one

for the AC values. And two for the chrominance channel one for the DC values and

one for the AC values. the size of the Huffman codes in a JPEG stream varies from 1

to 16 bit.

6.1.2 The Problem

Although the lookup and replace is an easy operation the problem arises when we want

to write the bit stream to the memory. A consecutive stream of codes varying in length

from one 1 to 16 bits has to be written to memory.

In this lab your task is to design and add new hardware to the processor that can be

used by an instruction to ease the bit stream writing, the idea is that it can be used as

a normal store operation where the length of the data to be stored can be speciﬁed and

the data stream will be packed in memory, i.e. each Huffman code will follow directly

after the previous Huffman code.

Preparation task 11

Suggest a method to handle the bit ﬁeld writing in software. Hint, look into the

jchuff.c

ﬁle in jpegﬁles.

Preparation task 12

Suggest a method to handle the bit ﬁeld writing in hardware.

6.2 Adding a New Instruction

In order to add a new instruction we ﬁrst need to ﬁnd a suitable instruction to use for

our purpose. Looking through the open RISC instruction set we ﬁnd that there are

some instructions used for storing double words (64-bits) and we can thus “kidnap”

one of these instructions,

l.sd

is a suitable instruction to use. Of course if you feel like

recoding the assembler you can name your instruction whatever you feel like. How

you use this instruction is up to you, remember that for one vlx operation you have to

specify the code and the size of the code.

6.2.1 Making the Processor Understand

In order to add a new instruction we need to make the processor aware of the instruction

we intend to add. The ﬁrst stage is to make some modiﬁcations to the instruction de-

coder. In the ﬁle or1200_ctrl.sv you will ﬁnd a number of

‘ifdef OR1200_SBIT_IMPL

preprocessor directives. Inside some of these you will ﬁnd a comment asking you to

write some code there. Find these places and add the missing code. Once this is

done correctly you should be able to use the

l.sd

instruction without causing an illegal

instruction exception but it will behave as a nop instruction.

6.2.2 Adding Special Purpose Registers

The hardware you are going to construct will use a number of special purpose reg-

isters to maintain observability and make it possible to handle some unusual situa-

1 2 ... 57 58 59 60 61 62 63 64 65 66 67 ... 81 82

Kommentare zu diesen Handbüchern

Keine Kommentare

Cypress DCT-1D Betriebsanweisung Seite 62

Kommentare zu diesen Handbüchern

Verwandte Produkte und Handbücher für Nein Cypress DCT-1D