arch/arm/lib/delay-loop.S

Source file repositories/reference/linux-study-clean/arch/arm/lib/delay-loop.S

File Facts

System
Linux kernel
Corpus path
arch/arm/lib/delay-loop.S
Extension
.S
Size
1237 bytes
Lines
68
Domain
Architecture Layer
Bucket
arch/arm
Inferred role
Architecture Layer: arch/arm
Status
atlas-only

Why This File Exists

CPU and platform-specific kernel glue: boot entry, traps, syscall entry, interrupts, page tables, context switch, and low-level barriers.

Dependency Surface

Detected Declarations

Annotated Snippet

#include <linux/linkage.h>
#include <linux/cfi_types.h>
#include <asm/assembler.h>
#include <asm/delay.h>

#ifdef CONFIG_ARCH_RPC
		.arch	armv4
#endif

		.text

.LC0:		.word	loops_per_jiffy
.LC1:		.word	UDELAY_MULT

/*
 * loops = r0 * HZ * loops_per_jiffy / 1000000
 *
 * r0  <= 2000
 * HZ  <= 1000
 */

SYM_TYPED_FUNC_START(__loop_udelay)
		ldr	r2, .LC1
		mul	r0, r2, r0		@ r0 = delay_us * UDELAY_MULT
		b	__loop_const_udelay
SYM_FUNC_END(__loop_udelay)

SYM_TYPED_FUNC_START(__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
		b	__loop_delay
SYM_FUNC_END(__loop_const_udelay)

		.align 3

@ Delay routine
SYM_TYPED_FUNC_START(__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
SYM_FUNC_END(__loop_delay)

Annotation

Implementation Notes