/* ARM assembly Raspberry PI */ /* program urandom.s */ /* Constantes */ .equ STDOUT, 1 @ Linux output console .equ EXIT, 1 @ Linux syscall .equ READ, 3 .equ WRITE, 4 .equ OPEN, 5 .equ CLOSE, 6 .equ O_RDONLY, 0 @ open for reading only .equ BUFFERSIZE, 4 @ random number 32 bits /* Initialized data */ .data szFileName: .asciz "/dev/urandom" @ see linux doc szCarriageReturn: .asciz "\n" /* datas error display */ szMessErreur: .asciz "Error detected.\n" szMessErr: .ascii "Error code hexa : " sHexa: .space 9,' ' .ascii " decimal : " sDeci: .space 15,' ' .asciz "\n" /* datas message display */ szMessResult: .ascii "Random number :" sValue: .space 12,' ' .asciz "\n" /* UnInitialized data */ .bss sBuffer: .skip BUFFERSIZE @ buffer result /* code section */ .text .global main main: ldr r0,iAdrszFileName @ File name mov r1,#O_RDONLY @ flags mov r2,#0 @ mode mov r7,#OPEN @ open file svc #0 cmp r0,#0 @ error ? ble error mov r8,r0 @ save FD mov r4,#0 @ loop counter 1: mov r0,r8 @ File Descriptor ldr r1,iAdrsBuffer @ buffer address mov r2,#BUFFERSIZE @ buffer size mov r7,#READ @ call system read file svc 0 cmp r0,#0 @ read error ? ble error ldr r1,iAdrsBuffer @ buffer address ldr r0,[r1] @ display buffer value ldr r1,iAdrsValue bl conversion10 ldr r0,iAdrszMessResult bl affichageMess add r4,#1 @ increment counter cmp r4,#10 @ maxi ? blt 1b @ no -> loop end: mov r0,r8 mov r7, #CLOSE @ call system close file svc #0 cmp r0,#0 blt error mov r0,#0 @ return code b 100f error: ldr r1,iAdrszMessErreur @ error message bl displayError mov r0,#1 @ return error code 100: @ standard end of the program mov r7, #EXIT @ request to exit program svc 0 @ perform system call iAdrsBuffer: .int sBuffer iAdrsValue: .int sValue iAdrszMessResult: .int szMessResult iAdrszFileName: .int szFileName iAdrszMessErreur: .int szMessErreur iAdrszCarriageReturn: .int szCarriageReturn /******************************************************************/ /* display text with size calculation */ /******************************************************************/ /* r0 contains the address of the message */ affichageMess: push {r0,r1,r2,r7,lr} @ save registers mov r2,#0 @ counter length */ 1: @ loop length calculation ldrb r1,[r0,r2] @ read octet start position + index cmp r1,#0 @ if 0 its over addne r2,r2,#1 @ else add 1 in the length bne 1b @ and loop @ so here r2 contains the length of the message mov r1,r0 @ address message in r1 mov r0,#STDOUT @ code to write to the standard output Linux mov r7, #WRITE @ code call system "write" svc #0 @ call system pop {r0,r1,r2,r7,lr} @ restaur registers bx lr @ return /***************************************************/ /* display error message */ /***************************************************/ /* r0 contains error code r1 : message address */ displayError: push {r0-r2,lr} @ save registers mov r2,r0 @ save error code mov r0,r1 bl affichageMess mov r0,r2 @ error code ldr r1,iAdrsHexa bl conversion16 @ conversion hexa mov r0,r2 @ error code ldr r1,iAdrsDeci @ result address bl conversion10S @ conversion decimale ldr r0,iAdrszMessErr @ display error message bl affichageMess 100: pop {r0-r2,lr} @ restaur registers bx lr @ return iAdrszMessErr: .int szMessErr iAdrsHexa: .int sHexa iAdrsDeci: .int sDeci /******************************************************************/ /* Converting a register to hexadecimal */ /******************************************************************/ /* r0 contains value and r1 address area */ conversion16: push {r1-r4,lr} @ save registers mov r2,#28 @ start bit position mov r4,#0xF0000000 @ mask mov r3,r0 @ save entry value 1: @ start loop and r0,r3,r4 @ value register and mask lsr r0,r2 @ move right cmp r0,#10 @ compare value addlt r0,#48 @ <10 ->digit addge r0,#55 @ >10 ->letter A-F strb r0,[r1],#1 @ store digit on area and + 1 in area address lsr r4,#4 @ shift mask 4 positions subs r2,#4 @ counter bits - 4 <= zero ? bge 1b @ no -> loop 100: pop {r1-r4,lr} @ restaur registers bx lr /***************************************************/ /* Converting a register to a signed decimal */ /***************************************************/ /* r0 contains value and r1 area address */ conversion10S: push {r0-r4,lr} @ save registers mov r2,r1 @ debut zone stockage mov r3,#'+' @ par defaut le signe est + cmp r0,#0 @ negative number ? movlt r3,#'-' @ yes mvnlt r0,r0 @ number inversion addlt r0,#1 mov r4,#10 @ length area 1: @ start loop bl divisionpar10U add r1,#48 @ digit strb r1,[r2,r4] @ store digit on area sub r4,r4,#1 @ previous position cmp r0,#0 @ stop if quotient = 0 bne 1b strb r3,[r2,r4] @ store signe subs r4,r4,#1 @ previous position blt 100f @ if r4 < 0 -> end mov r1,#' ' @ space 2: strb r1,[r2,r4] @store byte space subs r4,r4,#1 @ previous position bge 2b @ loop if r4 > 0 100: pop {r0-r4,lr} @ restaur registers bx lr /***************************************************/ /* division par 10 unsigned */ /***************************************************/ /* r0 dividende */ /* r0 quotient */ /* r1 remainder */ divisionpar10U: push {r2,r3,r4, lr} mov r4,r0 @ save value //mov r3,#0xCCCD @ r3 <- magic_number lower raspberry 3 //movt r3,#0xCCCC @ r3 <- magic_number higter raspberry 3 ldr r3,iMagicNumber @ r3 <- magic_number raspberry 1 2 umull r1, r2, r3, r0 @ r1<- Lower32Bits(r1*r0) r2<- Upper32Bits(r1*r0) mov r0, r2, LSR #3 @ r2 <- r2 >> shift 3 add r2,r0,r0, lsl #2 @ r2 <- r0 * 5 sub r1,r4,r2, lsl #1 @ r1 <- r4 - (r2 * 2) = r4 - (r0 * 10) pop {r2,r3,r4,lr} bx lr @ leave function iMagicNumber: .int 0xCCCCCCCD