hex.s

ARM_thumb 在embest 下的源码.可直接运行于embest 环境.

#; All assembler files must have at least one AREA directive at
#; the start. The AREA directive passes information to the linker
#; telling it where to place the code in memory (for example,
#; READONLY areas would be placed in a ROM segment).
#;
#        AREA    hex, CODE, READONLY
.text

#; Some definitions for system calls or SWIs supported by
#; 'armos'
#;
.equ	OS_WriteC, 0x00    		/* Write a character */
.equ	OS_Exit, 0x11    		/* Exit program */

#; ENTRY tells the linker where the entry point of an image is.
#; The linker in turn encodes this information in the image
#; header so the armulator knows where the application image
#; start.
#;
#        ENTRY

#; All applications are entered initially in ARM state so we
#; must write a couple of lines of ARM assembler to switch to
#; Thumb state. We tell the assembler we are going to do this
#; with the 'CODE32' directive.
#;
#        CODE32
.arm

#; Use the ARM BX instruction to switch into Thumb state. The
#; BX instruction will branch to the Thumb entry point. Add
#; one to the entry point to force the switch into Thumb state.
#;
        ADR     R0, Thumb_Entry+1
        BX      R0

#; The next section of code is Thumb code so tell the assembler
#; to assemble it as Thumb.
#;
        #CODE16
        .thumb

Thumb_Entry:
#; Now load several values in turn into R0 and call the Hex
#; Print routine.
#;
        MOV     R0, #0xED
        BL      Hex_Print

#; The number 0xAA55AA55 is too big to load into a register
#; using an immediate constant so we tell the assembler to
#; load it from memory by placing an '=' symbol before the
#; number. We do not need to tell the assembler where to
#; store the number in memory, it will decide that for us.
#;
        LDR     R0, =0xAA55AA55
        BL      Hex_Print

#; To load a negative number it is often easier to load the
#; postive value and then negate it as negative numbers cannot
#; be loaded using immediate constants.
#;
        MOV     R0, #10
        NEG     R0, R0
        BL      Hex_Print

#; Now exit the program cleanly
#;
        SWI     OS_Exit

Hex_Print:
#; Save registers used by this routine. Also save the link
#; register which contains the return address as this may be
#; destroyed by the call to SWI OS_WriteC if the code is
#; executing in supervisor mode.
        PUSH    {R0, R1, R2, LR}

        MOV     R1, R0          /* Enter with value to print in R0 */
                                /* Mov it to R1 as R0 needed for call */
                                /* to OS_WriteC. */
        MOV     R2, #8          /* Loop counter for 8 digits */
Loop1:
   		LSR     R0, R1, #28     /* Extract digits from R1 starting with 
                                   the most significant digit. */
        LSL     R1, #4          /* Shift up the digit to be used next
                                   time round the loop. */
        CMP     R0, #10         /* Convert R0 to a hex digit */
        BLT     Loop2
        ADD     R0, #'A'-'0'-10 /* Value >10 => add in extra to convert
                                   to range 'A' to 'F'. */
Loop2:
	   	ADD     R0, #'0'        /* Add in ASCII value for '0'. */
        SWI     OS_WriteC       /* Write the hex digit */
        SUB     R2, #1          /* Loop for each digit */
        BNE     Loop1           /* (SUB implicitly sets the condition codes) */
        MOV     R0, #0x0D
        SWI     OS_WriteC       /* Write a CR */
        MOV     R0, #0x0A
        SWI     OS_WriteC       /* Followed by a newline */
        POP     {R0, R1, R2, PC}/* Recover registers and return */

#; An END directive is always needed.
#;
.end
#        END