Cypress DCT-1D Guía de usuario descargar pdf (Pagina 64)

CHAPTER 6. LAB TASK 4 - CUSTOM INSTRUCTIONS

6.3.2 Data Path

The data path unit should deﬁned in the

or1200_vlx_dp

module, a stub can be found in

ﬁle or1200_vlx_dp.sv. The data path unit should contain all logic relevant for the

data manipulation needed. This unit will be responsible for aligning and merging the

incoming bits with the bits previously stored. Different solutions are possible, either

taking one or several clock cycles. This is basically a trade off between speed and

hardware. It is your task to implement this module of course in conjunction with how

you implemented the control unit.

6.3.3 Store Unit

The store unit should be deﬁned in the

or1200_vlx_su

module, a stub can be found in

ﬁle or1200_vlx_su.sv. The store unit is responsible for storing a full bit vector to

memory. A suggested solution is to take a 32 bit word and store it to main memory

one byte at a time, doing the zero stufﬁng if necessary. Remember that a 0xF F byte

has to be stored as two bytes 0x F F 0x00.

It is of course faster to store the data to the memory 32 bits at a time but keep in

mind that nothing more than byte alignment is ensured by jpegﬁles.

Important!

This is worth repeating, jpegﬁles only ensures byte aligned data.

If you do not understand the implications of this, consult some one in the

course staff before starting to implement your VLX unit.

6.3.4 Multi Cycle Instructions

Some instructions might be multicycle instructions, your solution will need to stall

the processor at certain points, at least when the bit buffer is stored to memory. This

is done by setting the

stall_cpu_o

signal high in the

or1200_vlx_top

module. When

high it will stop the cpu from fetching new instructions. This is useful, and so used,

when executing an instruction with indeterminable execution time, such as writing or

reading from memory.

6.3.5 Instruction Details

Although a lot of information about how the instruction is supposed to work is given

in this lab manual you have to work out the ﬁner details yourself. A good place to start

is to look into the jchuff.c ﬁle. Also all other place in the code surrounded by the

#ifdef HW_INST

(grep is a good tool) can be of interest. Also remember to design for

test, the more status you can view of your hardware when it is running for real, the

easier it will be for you to debug it if something fails.

6.4 Hardware Implementation

In this lab task you are supposed to construct much of the hardware yourself. You

have to modify a small part of the

or1200_lsu

module (Load Store Unit). Three special

purpose registers are already present in the VLX hardware, the

bit_reg

the

bit_reg_wr_pos

vlx_add_o

1 2 ... 59 60 61 62 63 64 65 66 67 68 69 ... 81 82

Comentarios a estos manuales

Sin comentarios

Cypress DCT-1D Guía de usuario Pagina 64

Comentarios a estos manuales

Relacionado con productos y manuales para No Cypress DCT-1D