assembly/timer.asm

SYS_TIMERFD_CREATE equ 0x142
SYS_TIMERFD_GETTIME equ 0x146
SYS_TIMERFD_SETTIME equ 0x145
SYS_READ equ 0x3


;timerfd_setttime()
;argument struct itimerspec contains 2 struct timespec
;struct timespec contains seconds as time_t (integer unixtimestamp?) and nanoseconds as long 

section .bss
	;timer filedescriptor
	tfd RESB 4
	;target memory for sys_timerfd_gettime
	ot RESB 16
	;timer struct interval
	itimer RESQ 2
	;timer struct init val
	vtimer RESQ 1
	;variable for timer read
	tval RESB 8

section .data
	tick equ 2000
	msg db 'tick',0xa
	msgl equ 5

section .text
	global _start

_start:

	;prepeare sys_timerfd_create
	mov eax, SYS_TIMERFD_CREATE
	mov ebx, 1
	mov ecx, 0
	int 0x80
	
	;get timer fd
	mov [tfd], eax

	;init timer
	;interval used for timer triggers
	mov [itimer], dword 0x05 ;sec
	mov [itimer + 4], dword 0x00 ;nanosecs
	;value - initial value must bes set to arm timer
	mov [itimer + 8], dword 0x05 ;secs
	mov [itimer + 12], dword 0x0 ;nanosecs

	;settime sys_timerfd_settime
	mov eax, SYS_TIMERFD_SETTIME
	mov ebx, [tfd]
	mov ecx, 0
	mov edx, itimer 
	mov esi, 0
	int 0x80


poll:
	;get time from fd 
	;not used just for debugging with strace
	mov eax, SYS_TIMERFD_GETTIME
	mov ebx, [tfd]
	mov ecx, ot
	int 0x80
	
	;sysread on fd from timer blocks til timer triggerd
	mov eax, SYS_READ
	mov ebx, [tfd]
	mov ecx, tval
	mov edx, 0x20
	int 0x80

	;print "tick"
	mov eax, 4
	mov ebx, 1
	mov ecx, msg
	mov edx, msgl
	int 0x80	

	jmp poll

exit:	
	mov eax, 1
	mov ebx, 0
	int 0x80