207b1150c0
Explain where the value for UDELAY_MULT and UDELAY_SHIFT come from. Also fix/clarify some comments pertaining to their usage in the assembly code. Signed-off-by: Nicolas Pitre <nico@linaro.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
63 lines
1.2 KiB
ArmAsm
63 lines
1.2 KiB
ArmAsm
/*
|
|
* linux/arch/arm/lib/delay.S
|
|
*
|
|
* Copyright (C) 1995, 1996 Russell King
|
|
*
|
|
* This program is free software; you can redistribute it and/or modify
|
|
* it under the terms of the GNU General Public License version 2 as
|
|
* published by the Free Software Foundation.
|
|
*/
|
|
#include <linux/linkage.h>
|
|
#include <asm/assembler.h>
|
|
#include <asm/delay.h>
|
|
|
|
.text
|
|
|
|
.LC0: .word loops_per_jiffy
|
|
.LC1: .word UDELAY_MULT
|
|
|
|
/*
|
|
* loops = r0 * HZ * loops_per_jiffy / 1000000
|
|
*
|
|
* r0 <= 2000
|
|
* HZ <= 1000
|
|
*/
|
|
|
|
ENTRY(__loop_udelay)
|
|
ldr r2, .LC1
|
|
mul r0, r2, r0 @ r0 = delay_us * UDELAY_MULT
|
|
ENTRY(__loop_const_udelay) @ 0 <= r0 <= 0xfffffaf0
|
|
ldr r2, .LC0
|
|
ldr r2, [r2]
|
|
umull r1, r0, r2, r0 @ r0-r1 = r0 * loops_per_jiffy
|
|
adds r1, r1, #0xffffffff @ rounding up ...
|
|
adcs r0, r0, r0 @ and right shift by 31
|
|
reteq lr
|
|
|
|
.align 3
|
|
|
|
@ Delay routine
|
|
ENTRY(__loop_delay)
|
|
subs r0, r0, #1
|
|
#if 0
|
|
retls lr
|
|
subs r0, r0, #1
|
|
retls lr
|
|
subs r0, r0, #1
|
|
retls lr
|
|
subs r0, r0, #1
|
|
retls lr
|
|
subs r0, r0, #1
|
|
retls lr
|
|
subs r0, r0, #1
|
|
retls lr
|
|
subs r0, r0, #1
|
|
retls lr
|
|
subs r0, r0, #1
|
|
#endif
|
|
bhi __loop_delay
|
|
ret lr
|
|
ENDPROC(__loop_udelay)
|
|
ENDPROC(__loop_const_udelay)
|
|
ENDPROC(__loop_delay)
|