xllp_checksum.s

Intel PXA270底层设备驱动代码

;******************************************************************************
;
;  COPYRIGHT (C) 2005 Intel Corporation.
;
;  This software as well as the software described in it is furnished under 
;  license and may only be used or copied in accordance with the terms of the 
;  license. The information in this file is furnished for informational use 
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;  a commitment by Intel Corporation. Intel Corporation assumes no 
;  responsibility or liability for any errors or inaccuracies that may appear 
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;  Except as permitted by such license, no part of this document may be 
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;  any means without the express written consent of Intel Corporation. 
;
;******************************************************************************
;  PURPOSE:
;      Checksum routine(s) for use by assembler and C code
;      It was created initially primarily to contain functions that may be needed
;      by both boot and kernel code.
;      If such routines exist in modules that make external references to other modules,
;      unresolved references are prone to be reported by the linker.
;      When the linker needs to pull in a module to resolve an external reference
;      it needs to resolve all external references in that module as well.
;      Functions in this file should therefore not make external references.

        AREA    |.text|, CODE, READONLY, ALIGN=5        ; Align =5 required for "ALIGN 32" to work
;
    INCLUDE xllp_ARM_macros.inc     ; for RETURN macro

; Functions made public by this file:
;
        EXPORT Xllp_SimpleChecksum
    
; This function is linked into both the boot loaders and the kernel image.
;     1. in resume code that is linked into the boot loader(s)
;     2. in suspend code that is linked into the kernel image
; It does not assume existance of a stack.
; However, if the SP is not zero it is assumed to be valid and registers used are preserved on the stack.
Xllp_SimpleChecksum FUNCTION
; Args:
;          r0 = buffer address
;          r1 = number of words
; Reg Use:
;          r0 = accumlating checksum (and checksum returned)
;          r1 = words left
;          r2 = pointer to next buffer word
;          r3 = current buffer word value
;
        ; if SP is non-zero save the registers we'll use
    cmp     sp, #0
    stmnedb sp!, {r1-r4, lr}               ; Push entry mode state onto our stack

    mov     r2, r0                         ; buffer pointer
    ldr     r0, =(0x5A72)                  ; Pick a non-zero seed.
2
    ldr     r3, [r2], #4                   ; get value and increment pointer
    add     r0, r0,   r3
    mov     r0, r0,   ROR #31              ; Rotate left by one bit position
    subs    r1, r1,   #1                   ; decrement words left
    bne     %B2

        ; if SP is non-zero restore regs we saved
    cmp     sp, #0
    ldmneia sp!, {r1-r4, lr}               ; Restore regs we used
    RETURN
    ENDFUNC
;**************************************************************************************************
    END