ECE 447: Lecture 15

Stack Operations

ECE 447: Stack after a function call

RTNL

RTNH

SP before

a function call

SP after

a function call

0

MAX_ADDRESS

ECE 447: Stack Operations

Subroutine call and return from subroutine

BSR

JSR

REL

N Z V C

– – – –

– – – –DIR, EXT, IND

RTS INH – – – –

ECE 447: Stack after an interrupt call

RTNL

RTNH

IYL

IYH

IXL

IXH

ABCC

SP before

an interrupt

SP after

an interrupt 0

MAX_ADDRESS

ECE 447: Stack Operations

Interrupt related instructionsand return from an interrupt

SWI

WAI

N Z V C

– – – –

– – – –

RTI INH – – – –

INH

INH

ECE 447: Stack Operations

INH

N Z V C

– – – –

PSH [A, B]PSH [X, Y]PUL [A, B]PUL [X, Y]

IMM, DIR, EXT, IND

N Z V C

0 –

Initialize and store stack pointer

DIR, EXT, IND 0 –

LDS

STS

Push and pull

ECE 447: Stack OperationsJump

Stack pointer manipulation

JMP – – – –DIR, EXT, IND

DES

TS [X, Y]

T [X, Y] S

INH

INH

INH

– – – –

– – – –

– – – –

INS

INH – – – –

Using the stack - Entering a function with a fixednumber of arguments and local variables

arg_2

arg_N

arg_2

arg_N...

arg_2

arg_N......

arg_2

arg_N...

RTNH

RTNL

RTNH

RTNL

RTNH

RTNL

Savedregisters

var_1

var_M...

callerfunction

calledfunction

SP

SP

IXarg_1

D

arg_1L

D

arg_1H

IXor

PSH

JSR orBSR

PSH

DES orPSHX

TSX

Localvariables

Returnaddress

Functionarguments

reg_1

reg_L...

reg_1

reg_L...

ECE447: Exiting a function: “called-cleanup” method

arg_2

arg_N

arg_2

arg_N......

arg_2

arg_N...

RTNH

RTNL

RTNH

RTNL

RTNH

RTNL

Savedregisters

var_1

var_M...

callerfunction

calledfunction

SP

SP

IXret

D

retL

D

retH

IXor

JMP 0,Y

PULY

INS

PUL

INS orPUL

Localvariables

Returnaddress

Functionarguments

reg_1

reg_L...

reg_1

reg_L...

Using the stack - Entering a function with a variablenumber of arguments

arg_1

arg_N

arg_1

arg_N...

arg_1

arg_N......

arg_1

arg_N...

RTNH

RTNL

RTNH

RTNL

RTNH

RTNL

Savedregisters

var_1

var_M...

callerfunction

calledfunction

SP

SP

IX

PSH

JSR orBSR

PSH

DES orPSHX

TSX

Localvariables

Returnaddress

Functionarguments

reg_1

reg_L...

reg_1

reg_L...

Using the stack - Exiting a function“caller-cleanup” convention

arg_1

arg_N

arg_1

arg_N...

arg_1

arg_N......

arg_1

arg_N...

RTNH

RTNL

RTNH

RTNL

RTNH

RTNL

Savedregisters

var_1

var_M...

callerfunction

calledfunction

SP

SP

IXret

D

retL

D

retH

IXor

PULz

RTS

PUL

INS orPULX

TXSLocal

variables

Returnaddress

Functionarguments

reg_1

reg_L...

reg_1

reg_L...

/* C version of main function */

#include <stdio.h>

extern long multadd(unsigned int a, unsigned char b, long c, long *pm);

long product, sum;

void main(void){ sum = multadd(258, 17, 32L, &product);}

main.c

In this example, long = 32bits

/* C version of the multadd function */

long multadd(unsigned int a, unsigned char b, long c, long *pm)/* this function returns a*b + c and writes a*b to the location of memory pointed out by pm*/{ long tmul; long tadd; tmul = a*b; *pm = tmul; tadd = tmul + c;

return tadd;}

multadd.c

* assembly language version of the main function

.global multadd

.global printf

.mri 1

section .bssproduct rmb 4sum rmb 4

amain.s (1)

section .textmain:; pushing arguments arg4 thru arg2 to the stack; arg4: pm = &product ldx #product pshx; arg3: c = 32L = 0x00000020 ldx #$0020 pshx ldx #$0000 pshx; arg2: b = 17 = 0x11 ldaa #$11 psha ; storing argument arg1 in the register D; arg1: a = 258 = 0x102 ldd #$102 jsr multadd

amain.s (2)

amultadd.s (1)

; assembly language version of the multadd function

tmul_offset EQU 0tadd_offset EQU 4a_offset EQU 8b_offset EQU 12c_offset EQU 13pm_offset EQU 17

0 - tmul

1 - tmul

2 - tmul

3 - tmul

4 - tadd

5 - tadd

6 - tadd

7 - tadd

10 - RTNH

11 - RTNL

12 - b

13 - c

14 - c

15 - c

16 - c17 - &product

18 - &product

8 - a

9 - a

SP

IX

amultadd.s (2)

section .text

multadd:;---------------------------------------------------------; Initialization sequence, similar for different functions;---------------------------------------------------------; storing D register

pshbpsha

; reserving space for two local variables; long tadd pshx pshx; long tmul pshx pshx

; IX set to point to the top of the stack tsx

amultadd.s (3a)

;---------------------------------------------------------; Part specific for the given function;---------------------------------------------------------; Multiplication;---------------------------------------------------------; tmul = a*b = (a_high * 2^8 + a_low) * b; ACCB = b

ldab b_offset,X; ACCA = LSB of a = a_low

ldaa a_offset+1,X; ACCD = b*a_low

mul; tmul = b*a_low

std tmul_offset+2,Xldd #0std tmul_offset,X

; ACCB = bldab b_offset,X

; ACCA = MSB of a = a_high ldaa a_offset,X

; ACCD = b*a_high mul; tmul= b*a_low + (2^8)*b*a_high

addd tmul_offset+1,Xstd tmul_offset+1,X

; *pm = tmulldy pm_offset,Xldd tmul_offset,Xstd 0,Yldd tmul_offset+2,Xstd 2,Y

amultadd.s (3b)

amultadd.s (4a)

;---------------------------------------------------------; Addition;---------------------------------------------------------; tadd = c

ldd c_offset,Xstd tadd_offset,Xldd c_offset+2,X

std tadd_offset+2,X; tadd = tadd + tmul

pshXclc

ldab #4loop ldaa tadd_offset+3,X

adca tmul_offset+3,Xstaa tadd_offset+3,Xdexdecbbne looppulx

; End of part specific for the given function

;---------------------------------------------------------; Exit sequence;---------------------------------------------------------

; restore value of the stack pointertxs

; return long result in registers IX and D; IX:D = tadd

ldx tadd_offset,Xldd tadd_offset+2,X

; deallocate space for local variables; repeat this 8 times

insinsinsinsinsins

amultadd.s (5)

insins

; remove register D from the stack puly; store return address in register IY puly ; repeat 7 times ins

insinsinsinsinsins

jmp 0,Y

end

amultadd.s (6)

RTNH

RTNL

main multadd

SP

SP

IX

$0102

D

LDXPSHX JSR

PSHD

PSHXPSHXPSHXPSHXTSX

&product

$20

LDD

$00$00$00$11

&product

$20$00$00$00$11

RTNH

RTNL

&product

$20$00$00$00$11

$02$01

RTNH

RTNL

&product

$20$00$00$00$11

$02$01

xxxx

xx xx xx

xxxx

xx

tmul

tadd

D=a

b

c

pm

0

4

8

12

13

17