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/*
* arch/xtensa/kernel/head.S
*
* Xtensa Processor startup code.
*
* This file is subject to the terms and conditions of the GNU General Public
* License. See the file "COPYING" in the main directory of this archive
* for more details.
*
* Copyright (C) 2001 - 2005 Tensilica Inc.
*
* Chris Zankel <chris@zankel.net>
* Marc Gauthier <marc@tensilica.com, marc@alumni.uwaterloo.ca>
* Joe Taylor <joe@tensilica.com, joetylr@yahoo.com>
* Kevin Chea
*/
#include <xtensa/cacheasm.h>
#include <asm/processor.h>
#include <asm/page.h>
/*
* This module contains the entry code for kernel images. It performs the
* minimal setup needed to call the generic C routines.
*
* Prerequisites:
*
* - The kernel image has been loaded to the actual address where it was
* compiled to.
* - a2 contains either 0 or a pointer to a list of boot parameters.
* (see setup.c for more details)
*
*/
.macro iterate from, to , cmd
.ifeq ((\to - \from) & ~0xfff)
\cmd \from
iterate "(\from+1)", \to, \cmd
.endif
.endm
/*
* _start
*
* The bootloader passes a pointer to a list of boot parameters in a2.
*/
/* The first bytes of the kernel image must be an instruction, so we
* manually allocate and define the literal constant we need for a jx
* instruction.
*/
.section .head.text, "ax"
.globl _start
_start: _j 2f
.align 4
1: .word _startup
2: l32r a0, 1b
jx a0
.text
.align 4
_startup:
/* Disable interrupts and exceptions. */
movi a0, XCHAL_PS_EXCM_MASK
wsr a0, PS
/* Preserve the pointer to the boot parameter list in EXCSAVE_1 */
wsr a2, EXCSAVE_1
/* Start with a fresh windowbase and windowstart. */
movi a1, 1
movi a0, 0
wsr a1, WINDOWSTART
wsr a0, WINDOWBASE
rsync
/* Set a0 to 0 for the remaining initialization. */
movi a0, 0
/* Clear debugging registers. */
#if XCHAL_HAVE_DEBUG
wsr a0, IBREAKENABLE
wsr a0, ICOUNT
movi a1, 15
wsr a0, ICOUNTLEVEL
.macro reset_dbreak num
wsr a0, DBREAKC + \num
.endm
iterate 0, XCHAL_NUM_IBREAK-1, reset_dbreak
#endif
/* Clear CCOUNT (not really necessary, but nice) */
wsr a0, CCOUNT # not really necessary, but nice
/* Disable zero-loops. */
#if XCHAL_HAVE_LOOPS
wsr a0, LCOUNT
#endif
/* Disable all timers. */
.macro reset_timer num
wsr a0, CCOMPARE_0 + \num
.endm
iterate 0, XCHAL_NUM_TIMERS-1, reset_timer
/* Interrupt initialization. */
movi a2, XCHAL_INTTYPE_MASK_SOFTWARE | XCHAL_INTTYPE_MASK_EXTERN_EDGE
wsr a0, INTENABLE
wsr a2, INTCLEAR
/* Disable coprocessors. */
#if XCHAL_CP_NUM > 0
wsr a0, CPENABLE
#endif
/* Set PS.INTLEVEL=1, PS.WOE=0, kernel stack, PS.EXCM=0
*
* Note: PS.EXCM must be cleared before using any loop
* instructions; otherwise, they are silently disabled, and
* at most one iteration of the loop is executed.
*/
movi a1, 1
wsr a1, PS
rsync
/* Initialize the caches.
* Does not include flushing writeback d-cache.
* a6, a7 are just working registers (clobbered).
*/
icache_reset a2, a3
dcache_reset a2, a3
/* Unpack data sections
*
* The linker script used to build the Linux kernel image
* creates a table located at __boot_reloc_table_start
* that contans the information what data needs to be unpacked.
*
* Uses a2-a7.
*/
movi a2, __boot_reloc_table_start
movi a3, __boot_reloc_table_end
1: beq a2, a3, 3f # no more entries?
l32i a4, a2, 0 # start destination (in RAM)
l32i a5, a2, 4 # end desination (in RAM)
l32i a6, a2, 8 # start source (in ROM)
addi a2, a2, 12 # next entry
beq a4, a5, 1b # skip, empty entry
beq a4, a6, 1b # skip, source and dest. are the same
2: l32i a7, a6, 0 # load word
addi a6, a6, 4
s32i a7, a4, 0 # store word
addi a4, a4, 4
bltu a4, a5, 2b
j 1b
3:
/* All code and initialized data segments have been copied.
* Now clear the BSS segment.
*/
movi a2, _bss_start # start of BSS
movi a3, _bss_end # end of BSS
1: addi a2, a2, 4
s32i a0, a2, 0
blt a2, a3, 1b
#if XCHAL_DCACHE_IS_WRITEBACK
/* After unpacking, flush the writeback cache to memory so the
* instructions/data are available.
*/
dcache_writeback_all a2, a3
#endif
/* Setup stack and enable window exceptions (keep irqs disabled) */
movi a1, init_thread_union
addi a1, a1, KERNEL_STACK_SIZE
movi a2, 0x00040001 # WOE=1, INTLEVEL=1, UM=0
wsr a2, PS # (enable reg-windows; progmode stack)
rsync
/* Set up EXCSAVE[DEBUGLEVEL] to point to the Debug Exception Handler.*/
movi a2, debug_exception
wsr a2, EXCSAVE + XCHAL_DEBUGLEVEL
/* Set up EXCSAVE[1] to point to the exc_table. */
movi a6, exc_table
xsr a6, EXCSAVE_1
/* init_arch kick-starts the linux kernel */
movi a4, init_arch
callx4 a4
movi a4, start_kernel
callx4 a4
should_never_return:
j should_never_return
/* Define some common data structures here. We define them
* here in this assembly file due to their unusual alignment
* requirements.
*/
.comm swapper_pg_dir,PAGE_SIZE,PAGE_SIZE
.comm empty_bad_page_table,PAGE_SIZE,PAGE_SIZE
.comm empty_bad_page,PAGE_SIZE,PAGE_SIZE
.comm empty_zero_page,PAGE_SIZE,PAGE_SIZE
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