mips procedure call interrupt io syscall

8/10/2019 MIPS Procedure Call Interrupt IO Syscall

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MIPS R2000 Assembly Language(Procedure Call, Interrupt, IO, Syscall)

CS 2 0


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Procedure Call

!"y do #e need $t% structured programming

reuse frequently used routine !"o ta&es care o' $t%

compiler for HLL programmer for assembly programming

!"at s"ould be done%1. save registers whose values will be needed after the call

who will do this job caller or callee2. save return address!. pass arguments to the callee

Anyt"$ng else% space to store local variables of the callee data structure to handle nested calls

stac"


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&

MIPS Procedure Calls

***

jal loc*

***

***

***

jr $ra*

loc#$ra

caller

callee

+hat if the callee calls another procedure


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Sa $ng Pr$ ate Reg$sters

use reg$sters as many as poss$ble they are much faster than memory (more than 1' times)

there are only a limited number of registers (!2 in /0 ) callee sa e s caller sa e

whichever that needs to save less registers MIPS con ent$ons

$s'..$s3 are callee saves $t'..$t4 are caller saves

problems registers are not enough a procedure calles another procedure solution#

you save5restore variables on the stac" carefully stac& 'rame $t $s 'or a comp$ler


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Stac& *rame

purpose store data used by a procedure in a single frame

data can be accessed using a single pointer ($fp) within a procedure the stac" may be used for other purpose e6pression evaluation

accessing data using $sp can be tric"y stac" is used for other purposes Is $t really necessary%

yes% for recursive calls yes% for comple6 chained procedure calls no% for simple programs compilers use it 7

contents $n a stac& 'rame arguments other than stored in a'..a! saved register values variables local to the procedure


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Stac& *rame

stack

old $fpargument 5

argument 6

savedregisters

localvariables

$spstack growsand shrinks

duringexpressionevaluation

.

9 of procedue :

9 of procedue ;

9 of procedue eroes

8a8 not a number >ero5>ero

exponent fraction

( ? $53normali1ed

fraction

% denormali1edfraction

$55 %

% %

$55 non21ero


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MIPS *loat$ng Po$nt Reg$sters

FGR 0

Floating PointGeneral Purpose Registers

(FGR)

FGR 1

FGR

FGR !

FGR "

FGR #

FGR $

FGR %FGR !0

FGR !1

Floating PointRegisters (FPR)

least

mostFPR 0

least

mostFPR

least

mostFPR !0

least

mostFPR $


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MIPS *P Instruct$ons

&P 'escription

l.d !f3" addr s.s !f3" addr mov.d !f3" !f6

ctc( !@" rdcfc( !6" rd

cvt.s.fmtcvt.d.fmtcvt.w.fmt

load d2word to !f3store s2word from !f3move word

move control word to PAmove from

convert to single Pconvert to double Pconvert to fixed point

fmt Formats single precisiond double precisionw binar fixed point &integer'

e6maple# cvt.s.w 9Edest% 9Esrccvt.d.w 9Edest% 9Esrccvt.d.s 9Edest% 9Esrc


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2!

MIPS *P Instruct$ons (2)

&P 'escription

add.fmtsub.fmtmul.fmtdiv.fmtabs.fmt

mov.fmtneg.fmt

addsubstractmultipldivideabsolute value

move fp to fpnegate

compare and branch

c.cond.format (" $bc(t labelbc(f label

cond ConditioneD" le" lt" t" f" or" nlt" gt" ..result sets a flag in PAbranch instruction on this flag

BC(, label 0 branch if trueBC( label 0 branch if false

e6maple# add.s 9rdest% 9Esrc1% 9Esrc2 add.d 9rdest% 9Esrc1% 9Esrc2 sub.s 9rdest% 9Esrc1% FEsrc2

e6maple# c.eq.s 9Esrc1% 9Esrc2 bc1t 666


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2&

./cept$on

./cept$on > unprogrammed control trans'er

system ta"es action to handle the e6ception must record the address of the offending instruction

returns control to user must save - restore user state

user program

normal control flow seDuential" )umps" branches" calls" returns

E stemFxceptionGandler Fxception

return from

exception


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#o ypes o' ./cept$ons

Interrupts caused by e6ternal events

asynchronous to program e6ecution may be handled between instructions simply suspend and resume user program

raps caused by internal events

e6ceptional conditions (overflow) errors (parity) faults (non?resident page)

synchronous to program e6ecution condition must be remedied by the handler instruction may be retried or simulated and program continued or program may

be aborted


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MIPS Con ent$on

e6ception means any une6pected change in control flow% without distinguishinginternal or e6ternal

use the term interrupt only when the event is e6ternally caused.

Type of event From where? MIPS terminology

05G device request C6ternal 0nterrupt0nvo"e G from user program 0nternal C6ception:rithmetic overflow 0nternal C6ception

Ising an undefined instruction 0nternal C6ceptionHardware malfunctions Cither C6ception or 0nterrupt


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Address$ng t"e ./cept$on andler

rad$t$onal Approac"4 Interupt Bector < J? /C/K 0 Mbase D cause NN ''O

!3'% 8'''% a6% 8'68 % . . .

MIPS Approac"4 '$/ed entry < J? CP


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Sa $ng State

Pus" $t onto t"e stac& a6% 8"% 8'68

Sa e $t $n spec$al reg$sters /0 C


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!1

Cause Reg$ster

Pend$ng $nterrupt 6 "ard#are le els4 b$t set $' $nterrupt occurs but not yet ser $ced handles cases when more than one interrupt occurs at same time% or while records

interrupt requests when interrupts disabled ./cept$on Code encodes reasons 'or $nterrupt

' (0RQ) BS e6ternal interrupt 1=! BS QL; related & (:FFEL) BS address error e6ception (load or instr fetch) , (:FFE ) BS address error e6ception (store) (0;I ) BS bus error on instruction fetch 3 (F;I ) BS bus error on data fetch

8 ( yscall) BS yscall e6ception 4 (;T Q) BS ;rea"point e6ception 1' (E0) BS Eeserved 0nstruction e6ception 12 (G 9) BS :rithmetic overflow e6ception

Status:6 :0

Pend$ng

6 2

Code


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!!

Input and Output

IO


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!&

SPIM IO

memory mapped IO & registers are mapped to memory locations

to read data 'rom &eyboard Eeady bit means that the UEeceived dataV register has a data. +hen a data arrives% interrupt is raised if it is enabled .

(

9nterruptenable

ead

(Inused

eceiver control&%xffff%%%%'

4

eceived b te

Inused

eceiver data&%xffff%%%3'


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SPIM ll


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!3

SPIM syscall mo e a04 tli 04 1

s3scall

ser $ce call code arguments results print integer 1 int in $a'

print float 2 float in $a' print double ! double in $a' print string & addr of string in $a'

read integer , int in $v'read float float in $v'read double 3 double in $v'read string 8 $a'Bbuffer% $a1Blength

sbr" 4 $a' B amount addr in $v'e6it 1'

mips procedure call interrupt io syscall

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