delay.s

来自「AT91所有开发板的资料 AT91所有开发板的资料」· S 代码 · 共 71 行

        SUBT    Evaluator Support             > delay.s
;
; $Revision:  $
;   $Author:  $
;     $Date:  $
;
; Copyright (c) 1996 Advanced RISC Machines Limited
; All Rights Reserved
;
; ---------------------------------------------------------------------

                GET     listopts.s
                GET     lolevel.s

                ASSERT  (listopts_s)
old_opt         SETA    {OPT}
                OPT     (opt_off)       ; disable listing of include files

; ---------------------------------------------------------------------

    [   (:LNOT: :DEF: etherser_s)

	GBLL    delay_s
delay_s	SETL    {TRUE}

	AREA    |delay|, CODE, READONLY

; ---------------------------------------------------------------------

;
; delay - delay for a given number of microseconds
;
; This routine is actually hopelessly inaccurate, as it depends upon
; the system clock frequency, and the speed of the memory it is running
; from.  It is written assuming that it is running on an ARM7T
; clocked at 25MHz in single-cycle SSRAM; if this is not the case,
; then it will just delay for proportionately shorter or longer.
;

;
; we loop 4 times for every microsecond.  This gives a total of 28 ARM7T
; clocks per microsecond - an error of 12%, which we can probably cope with.
;
; Note that, with the SRAM on the Evaluator, with 1 wait state at 50Mhz, the
;effective  access time is the same as for the 25MHz case mentioned above.
;
	EXPORT  delayloop
delayloop	
	mov	r0, r0, lsl #2

5	mov	r0, r0
	subs	r0, r0, #1
	moveq	pc, lr
	b	%5

; ---------------------------------------------------------------------

    ]   ; delay_s

	EXPORT	traceRegs
traceRegs


        OPT     (old_opt)   ; restore previous listing options

; ---------------------------------------------------------------------

        END

; EOF delay.s