Assalam o Alaikum to all.
Dear friends I want to know what are the thread control instructions in multitasking of assembly? Can anyone please help me? Thanks in advance
Yaseen16 0 Newbie Poster
Ancient Dragon 5,243 Achieved Level 70 Team Colleague Featured Poster
What processor? There is no such thing on Intel or Intel compatible processors that I'm aware of. Implementing threading in assembly language would be exceedingly difficult. Better to do it in a higher language such as C.
Yaseen16 0 Newbie Poster
The processor is Intel IAPX88 Architecture
Yaseen16 0 Newbie Poster
;elementary multitasking of two threads
[org 0x0100]
jmp start
; ax, bx, ip, cs, flags storage area
taskstates: dw 0, 0, 0, 0, 0 ;task0 regs
dw 0, 0, 0, 0, 0 ;task1 regs
dw 0, 0, 0, 0, 0 ;task2 regs
current: db 0 ;index of current task
chars: db '\|/-' ;shapes to form a bar
;one task to be multitasked
taskone: mov al, [chars+bx] ;read the next shape
mov [es:0], al ;write at the top left of screen
inc bx ;increment to next shape
and bx, 3 ;taking modulus by 4
jmp taskone ;infinite task
;second task to be multitasked
tasktwo: mov al, [chars+bx] ;read the next shape
mov [es:158], al ;write at top right of screen
inc bx ;increment to next shape
and bx, 3 ;taking modulus by 4
jmp tasktwo ;infinite task
;timer interrupt service routine
timer: push ax
push bx
mov bl, [cs:current] ;read index of current task
mov ax, 10 ;space used by one task
mul bl ;multiply to get start of task
mov bx, ax ;load start of task in bx
pop ax ;read original value of bx
mov [cs:taskstates+bx+2], ax ;space for current task
pop ax ;read original value of ip
mov [cs:taskstates+bx+4], ax ;space for current task
pop ax ;read original value of cs
mov [cs:taskstates+bx+6], ax ;space for current task
pop ax ;read original value of flags
mov [cs:taskstates+bx+8], ax ;space for current task
inc byte [cs:current] ;update current task index
cmp byte [cs:current], 3 ;is task index out of range
jne skipreset ;no, proceed
mov byte [cs:current], 0 ; yes, reset to task 0
skipreset: mov bl, [cs:current] ;read index of current task
mov ax, 10 ;space used by one task
mul bl ;multiply to get start of task
mov bx, ax ;load start of task in bx
mov al, 0x20
out 0x20, al ;send EOI to PIC
push word [cs:taskstates+bx+8] ;flags of new task
push word [cs:taskstates+bx+6] ;cs of new task
push word [cs:taskstates+bx+4] ;ip of new task
mov ax, [cs:taskstates+bx+0] ;ax of new task
mov bx, [cs:taskstates+bx+2] ;bx of new task
iret ;return to new task
start: mov word [taskstates+10+4], taskone ;initialize ip
mov [taskstates+10+6], cs ;initialize cs
mov word [taskstates+10+8], 0x0200 ;initialize flags
mov word [taskstates+20+4], tasktwo ;initialize ip
mov [taskstates+20+6], cs ;initialize cs
mov word [taskstates+20+8], 0x0200 ;initialize flags
mov word [current], 0 ;set current task index
xor ax, ax
mov es, ax ;point es to IVT base
cli
mov word [es:8*4], timer
mov [es:8*4+2], cs ;hook timer interrupt
mov ax, 0xb800
mov es, ax ;point es to video base
xor bx, bx ;initialize bx for tasks
sti
jmp $The thread control instruction is in this code but I am unable to find that instruction. Kindly help me to find out that thread control instruction
Ancient Dragon 5,243 Achieved Level 70 Team Colleague Featured Poster
See line 62. iret instruction returns control from an interrupt handler. On MS-DOS interrupt handlers are common to process hardware and software interrupts.
The program actually begins at the label named Start on line 64. It initializes a timer interrupt handler then jumps somewhere (line 82).
These are not really threads as we know them in MS-Windows and *nix. Nor will you be able to run that assembly code under MS-Windows.
coffeeuncle 0 Newbie Poster
This is the section where task switching is made.
Has 3 tasks switching one after the other, the calling task (program itself) and taskone and tasktwo.
Seems to be a sample program that writes something on the screen.
Can not test because I dont have DOS and my WIN XP does not accept to hook "DOS" interrupts I think.
[U]inc byte [cs:current][/U] ;update current task index
cmp byte [cs:current], 3 ;is task index out of range
jne skipreset ;no, proceed
mov byte [cs:current], 0 ; yes, reset to task 0 Be a part of the DaniWeb community
We're a friendly, industry-focused community of developers, IT pros, digital marketers, and technology enthusiasts meeting, networking, learning, and sharing knowledge.