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COMP541COMP541

Final Missing Pieces of Final Missing Pieces of MIPS: Adding Memory & MIPS: Adding Memory &

I/OI/O

Montek SinghMontek Singh

Apr 11, 2012Apr 11, 2012

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Summary of Remaining Labs, etc.Summary of Remaining Labs, etc. HW #2 (last one) assigned later todayHW #2 (last one) assigned later today

due Fri April 20due Fri April 20

Lab DemosLab Demos Fri April 20, 1-2:50pmFri April 20, 1-2:50pm

grade by 4/23grade by 4/23 Mon April 23, 1-3:30pmMon April 23, 1-3:30pm

grade by 4/25grade by 4/25 Wed April 25, 1-2:15pm: final chance for demosWed April 25, 1-2:15pm: final chance for demos

grade by 4/27grade by 4/27

OptionalOptional Take-Home Test #2 Take-Home Test #2 assigned April 20assigned April 20 due anytime up until Apr 30, 3pm (final exam slot)due anytime up until Apr 30, 3pm (final exam slot)

Tasks for Lab Final Project/DemoTasks for Lab Final Project/Demo April 13: Lab 10 CompletedApril 13: Lab 10 Completed

Show:Show:show a complete and working Lab 10show a complete and working Lab 10

I will show you how to:I will show you how to:add keyboard/joystick/mouseadd keyboard/joystick/mouse integrate your VGA display codeintegrate your VGA display code

April 13-20: Demo developmentApril 13-20: Demo development Do:Do:

add any new instructions you needadd any new instructions you needdevelop your game/demo app (keep it simple!)develop your game/demo app (keep it simple!)

April 20, 23, 25:April 20, 23, 25: Show:Show:

show a complete and working final demoshow a complete and working final demo

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A few tips on finishing up your A few tips on finishing up your MIPSMIPS Sign extension: simpleSign extension: simple

assume all of your I-type assume all of your I-type instructions are signedinstructions are signede.g., lw, sw, addi, beqe.g., lw, sw, addi, beq

thus, simply sign-extend thus, simply sign-extend everyevery immediate operand immediate operand just extend value of bit 15 to just extend value of bit 15 to

upper 16 bitsupper 16 bits

Add any other instrs Add any other instrs neededneeded sltslt could be very useful for could be very useful for

loops!loops! you can do without all you can do without all

“unsigned” instructions“unsigned” instructions

Do everything step-by-Do everything step-by-step!step! 4

This is your single-cycle MIPSThis is your single-cycle MIPS

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MemoriesMemories Word widthWord width

both instruction (IM) and data memories (DM) have both instruction (IM) and data memories (DM) have 32-bit words32-bit wordsbe careful about word vs. byte addressesbe careful about word vs. byte addresses i.e., whether or not to multiply/divide by 4i.e., whether or not to multiply/divide by 4

size IM so it can hold your code (say, 200 instructions)size IM so it can hold your code (say, 200 instructions) size DM so it can hold all your data (say, 100 words)size DM so it can hold all your data (say, 100 words)lwlw and and swsw should suffice should suffice

skip skip lblb and and sbsb they could be done in softwarethey could be done in software

Memory-Mapped I/OMemory-Mapped I/O Simple technique for accessing I/OSimple technique for accessing I/O

give each I/O device a “fake” memory addressgive each I/O device a “fake” memory address i.e., CPU reads and writes a specific range of memory i.e., CPU reads and writes a specific range of memory

locations for I/O deviceslocations for I/O devicesusing using lwlw and and swswpretending I/O devices were simply memory locationspretending I/O devices were simply memory locationsnet effect is reading and writing I/Onet effect is reading and writing I/O

each device is assigned its own range of memoryeach device is assigned its own range of memory““address space”address space”

example:example:data memory from ’h0000_0000 to ’h0000_FFFFdata memory from ’h0000_0000 to ’h0000_FFFFVGA display (screen memory) from ’h1000_0000 to VGA display (screen memory) from ’h1000_0000 to

’h1000_03FF’h1000_03FF joystick status at ’h1100_0000joystick status at ’h1100_0000mouse status at ’h1100_0004mouse status at ’h1100_0004keyboard status at ’h1100_0008 …keyboard status at ’h1100_0008 …

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Memory MapMemory Map

Data Memory

CharacterMemory

0000 0000

0000 FFFF

1000 03FF

1100 0000

Do you test all bits in your memory decoder? Up to you.

Keep in mind:Keep in mind: your character memory your character memory

may have different word may have different word widthswidths

e.g., x1, or x8, etc.e.g., x1, or x8, etc. you may need to do you may need to do

some address and data some address and data conversionconversion

joystick, etc.

gap

gap

Memory MapMemory Map How to do in Verilog?How to do in Verilog?

Let’s do this interactively!Let’s do this interactively!

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Adding I/OAdding I/O Look at memory-mapped I/OLook at memory-mapped I/O Conceptually like thisConceptually like this

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In RealityIn Reality Isolated from CPUIsolated from CPU On standard busesOn standard buses

PCIPCI

Ours will typically be simplerOurs will typically be simpler Just memory addressesJust memory addresses

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Joystick, mouse, etc.Joystick, mouse, etc. YouYou’’ll add joystick or keyboard (or both) into ll add joystick or keyboard (or both) into

memory locations that you can readmemory locations that you can read e.g., at two locations right above character memory e.g., at two locations right above character memory

I will show you on FriI will show you on Fri

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How Does Processor Begin?How Does Processor Begin? One way is to initialize PC to 0One way is to initialize PC to 0

or some other predefined addressor some other predefined address

Another possibility is to have a resetAnother possibility is to have a reset each time you hit a reset button, PC starts again at 0each time you hit a reset button, PC starts again at 0

Make sure to have instructions thereMake sure to have instructions there Modern computers have flash memory to boot CPU or Modern computers have flash memory to boot CPU or

go to configuration utilitygo to configuration utility On (very) old computers had to enter boot program On (very) old computers had to enter boot program

on front panelon front panel

SummarySummary Now we are done with creating a CPU!Now we are done with creating a CPU!

Start creating your final demo!Start creating your final demo!

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