133 lines
3.6 KiB
ArmAsm
133 lines
3.6 KiB
ArmAsm
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/***************************************************************************
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* __________ __ ___.
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* Open \______ \ ____ ____ | | _\_ |__ _______ ___
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* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
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* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
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* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
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* \/ \/ \/ \/ \/
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* $Id$
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*
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* Copyright (C) 2003 by Magnus Holmgren
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*
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* All files in this archive are subject to the GNU General Public License.
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* See the file COPYING in the source tree root for full license agreement.
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*
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* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
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* KIND, either express or implied.
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*
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****************************************************************************/
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.section .icode,"ax",@progbits
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.align 4
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.global _descramble
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.type _descramble,@function
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/* Descramble a block of byte data, from source to dest, processing len
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* bytes. Size only limited by the len argument. Note that len must
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* be an even multiple of 4 (something rolo_load() already assumes.
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* (Does the Archos firmware loader also require that?).
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*
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* Returns the 16-bit "sum" checksum of the descrambled data.
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*
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* Arguments:
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* r4 - source (unsigned char*)
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* r5 - dest (unsigned char*)
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* r6 - len (unsigned int)
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*/
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/* Register usage:
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* i - r0
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* i4 - r1
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* checksum - r2
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* addr - r3
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* source - r4
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* dest - r5
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* len - r6
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* len4 - r7
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* data - r8
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* temp - r9
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*/
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_descramble:
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mov.l r8,@-r15
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mov.l r9,@-r15
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mov #0,r0 /* i = 0 */
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mov #0,r1 /* i4 = i / 4 */
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mov #0,r2 /* checksum = 0 */
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mov r4,r3 /* addr = source */
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mov r6,r7
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shlr2 r7 /* len4 = len / 4 */
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.loop:
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mov.b @r3,r8 /* data = source[addr] */
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add r7,r3 /* addr += len4 */
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extu.b r8,r8 /* we want the data extended unsigned */
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shlr r8 /* start rotate right of low byte */
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movt r9 /* get bit 0 that was shifted out */
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shll8 r9
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shlr r9 /* move it to bit 7 */
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or r9,r8 /* finish rotate right */
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not r8,r8
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extu.b r8,r8
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mov.b r8,@(r0,r5) /* dest[i] = data */
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add r8,r2 /* checksum += data[i] */
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add #1,r0 /* i++ */
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tst #3,r0 /* reset addr? */
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bf .loop
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add #1,r1 /* i4++ */
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mov r4,r3
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add r1,r3 /* addr = source + i4 */
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cmp/hs r6,r0 /* all done? */
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bf .loop
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/* 17 cycles if no "reset," 22 if reset => average 18.25 cycles per
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* byte, assuming no wait states from reads or writes. "Old" algorithm
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* needed 24-26 cycles per byte, under the same assumptions.
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*/
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mov.l @r15+,r9
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mov.l @r15+,r8
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rts
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extu.w r2,r0
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/* Move len bytes from source to dest (which must be suitably aligned for
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* long moves) and jump to dest + 0x200.
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*
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* Arguments:
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* r4 - source
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* r5 - dest
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* r6 - len
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*/
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.global _rolo_restart
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.type _rolo_restart,@function
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_rolo_restart:
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mov.w .offset,r0
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mov r5,r7
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add r0,r7 /* start_func() */
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mov r6,r0
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shlr2 r0
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add #1,r0
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.copy:
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mov.l @r4+,r1
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add #-1,r0
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mov.l r1,@r5
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add #4,r5
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cmp/eq #0,r0
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bf .copy
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jmp @r7
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nop
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.offset:
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.word 0x200
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.end:
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.size _descramble,.end-_descramble
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