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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>
62 lines
1.2 KiB
ArmAsm
62 lines
1.2 KiB
ArmAsm
/*
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* linux/arch/arm/lib/delay.S
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*
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* Copyright (C) 1995, 1996 Russell King
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#include <linux/linkage.h>
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#include <asm/assembler.h>
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#include <asm/delay.h>
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.text
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.LC0: .word loops_per_jiffy
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.LC1: .word UDELAY_MULT
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/*
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* loops = r0 * HZ * loops_per_jiffy / 1000000
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*
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* r0 <= 2000
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* HZ <= 1000
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*/
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ENTRY(__loop_udelay)
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ldr r2, .LC1
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mul r0, r2, r0 @ r0 = delay_us * UDELAY_MULT
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ENTRY(__loop_const_udelay) @ 0 <= r0 <= 0xfffffaf0
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ldr r2, .LC0
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ldr r2, [r2]
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umull r1, r0, r2, r0 @ r0-r1 = r0 * loops_per_jiffy
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adds r1, r1, #0xffffffff @ rounding up ...
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adcs r0, r0, r0 @ and right shift by 31
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reteq lr
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.align 3
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@ Delay routine
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ENTRY(__loop_delay)
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subs r0, r0, #1
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#if 0
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retls lr
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subs r0, r0, #1
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retls lr
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subs r0, r0, #1
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retls lr
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subs r0, r0, #1
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retls lr
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subs r0, r0, #1
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retls lr
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subs r0, r0, #1
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retls lr
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subs r0, r0, #1
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retls lr
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subs r0, r0, #1
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#endif
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bhi __loop_delay
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ret lr
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ENDPROC(__loop_udelay)
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ENDPROC(__loop_const_udelay)
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ENDPROC(__loop_delay)
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