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/***************************************************************************
* __________ __ ___.
* Open \______ \ ____ ____ | | _\_ |__ _______ ___
* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
* \/ \/ \/ \/ \/
* $Id$
*
* Copyright (C) 2004 by Jens Arnold
*
* All files in this archive are subject to the GNU General Public License.
* See the file COPYING in the source tree root for full license agreement.
*
* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
* KIND, either express or implied.
*
****************************************************************************/
.section .icode,"ax",@progbits
.align 2 /* this aligns to 2^2=4 byte bounday */
.global _descramble
.type _descramble,@function
/* Descramble a block of byte data, from source to dest, processing len
* bytes. Size only limited by the len argument. Note that len must
* be an even multiple of 4 (something rolo_load() already assumes.
* (Does the Archos firmware loader also require that?).
*
* Returns the 16-bit "sum" checksum of the descrambled data.
*
* Arguments:
* r4 - source (unsigned char*)
* r5 - dest (unsigned char*)
* r6 - len (unsigned int)
*
* Register usage:
* r0 - data
* r1 - temp
* r2 - checksum
* r3 - current src address
* r4 - source
* r5 - dest
* r6 - len -> source_end
* r7 - dest_end
* r8 - len / 4
*/
_descramble:
mov.l r8,@-r15
mov r6,r8
shlr2 r8 /* r8 = len / 4 */
mov r5,r7
add r6,r7 /* dest_end = dest + len */
add r4,r6 /* source_end = source + len */
mov r4,r3 /* addr = source */
mov #0,r2 /* checksum = 0 */
.loop:
mov.b @r3,r0 /* data = *addr */
add r8,r3 /* addr += len / 4 */
extu.b r0,r0 /* zero extend data byte */
swap.b r0,r1 /* byte swap low word to temp */
or r1,r0 /* r0's two lower bytes now identical */
shlr r0 /* -> this equals "rotr.b r0" now */
not r0,r0 /* negate */
extu.b r0,r0 /* zero extend low byte (only needed for sum) */
mov.b r0,@r5 /* *dest = data */
add r0,r2 /* checksum += data */
add #1,r5 /* dest++ */
cmp/hi r3,r6 /* addr < source_end ? */
bt .loop
add #1,r4 /* source++ */
mov r4,r3 /* addr = source */
cmp/hi r5,r7 /* dest < dest_end */
bt .loop
/* 15 clock cycles if no reset of source address, 19 if reset,
* avg. 16 cycles per byte. Magnus' Version needed 17-22 cycles per byte
*/
mov.l @r15+,r8
rts
extu.w r2,r0
/* Move len bytes from source to dest (which must be suitably aligned for
* long moves) and jump to dest + 0x200.
*
* Arguments:
* r4 - source
* r5 - dest
* r6 - len
*/
.align 2
.global _rolo_restart
.type _rolo_restart,@function
_rolo_restart:
mov r5,r0
sub r4,r0 /* r0 = dest - source */
add #-4,r0 /* adjust for early increment */
add r4,r6 /* r6 = source + len */
.copy: /* loop takes 6 cycles per longword */
mov.l @r4+,r1
cmp/hi r4,r6
mov.l r1,@(r0,r4)
bt .copy
mov.l @r5+,r0 /* start address from image */
jmp @r0
mov.l @r5+,r15 /* stack pointer from image */
.end:
.size _descramble,.end-_descramble
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