assembly - Assembler stuck in sys_read loop -

i've written piece of code takes number in ascii characters prompt, converts decimal number , stores in 'dnumber'. conversion has been checked , goes well. goes wrong @ prompt. seems stuck in infinite loop while asking user ascii character number. want program stop asking input when user presses enter, termination value never seems reached though think i've set way.

i've asked 2 related questions on forum lately , showed don't understand system calls properly. i've read documentation on 'http://www.tutorialspoint.com/assembly_programming', 'http://cs.lmu.edu/~ray/notes/nasmtutorial/' , of 'http://www.x86-64.org/documentation/abi.pdf' , apparently i'm still not getting it. can show me light.

here compiler info:

nasm -f elf64 convinput.asm  ld -s -o convinput convinput.o 

here prompt:

$ ./convinput enter number , press enter:  123  123 123 

as can see i've pressed enter twice, prompt still asks input.

here code:

section     .text  global _start  _start:      mov     eax, 4     mov     ebx, 1     mov     edx, lenmsg1     mov     ecx, msg1     int     80h      xor     eax, eax     xor     ebx, ebx     xor     edx, edx     mov     esi, data     call    input      mov     esi, data     movzx   ecx, byte [dignum]     xor     ebx,ebx    ; clear ebx      call    string_to_int      mov     dword [dnumber], eax      mov     eax, 1     mov     ebx, 0     int     80h  input:     mov  eax, 3     mov  ebx, 0     mov  ecx, esi     mov  edx, 1     int  80h      inc  byte [dignum]     cmp  byte [esi], 13     inc  esi     jne  input     ret  string_to_int:   xor   ebx,ebx   movzx eax, byte [esi]   inc   esi   sub   al,'0'    ; convert ascii number4   mov   ebx, 10   mul   ebx   add   ebx,eax   ; ebx = ebx*10 + eax     dec   byte [dignum]   cmp   byte [dignum], 0   jne   string_to_int   mov   eax,ebx   ret   section .bss      dignum  resb 1     data    resb 1000     dnumber resd 1 section .data     msg1 db 'enter number , press enter: ', 10, 0     lenmsg1 equ $ -msg1      ; esi = pointer string convert     ; ecx = number of digits in string (must > 0)     ; output:     ; eax = integer valu 

judging values put eax using 32-bit syscall table, on linux different 64-bit one.

you can see syscalls (and arguments) called running program under strace.