blob: 8aeb396280624fe3e4c7455301aaefac7c5abd0a [file] [log] [blame]
/*
* Copyright (c) 2016 Cadence Design Systems, Inc.
* SPDX-License-Identifier: Apache-2.0
*/
/*
* Control arrives here at _start from the reset vector or from crt0-app.S.
*/
#include <xtensa_rtos.h>
/* Exports */
.global _start
/*
* Imports
* __stack from linker script (see LSP Ref Manual)
* _bss_table_start from linker script (see LSP Ref Manual)
* _bss_table_end from linker script (see LSP Ref Manual)
* _Cstart Entry point into Zephyr C domain
* __stack from linker script (see LSP Ref Manual)
*/
.global __start
.type _Cstart, @function
/* Macros to abstract away ABI differences */
#if __XTENSA_CALL0_ABI__
# define CALL call0
# define CALLX callx0
# define ARG1 a2 /* 1st outgoing call argument */
# define ARG2 a3 /* 2nd outgoing call argument */
# define ARG3 a4 /* 3rd outgoing call argument */
# define ARG4 a5 /* 4th outgoing call argument */
# define ARG5 a6 /* 5th outgoing call argument */
#else
# define CALL call4
# define CALLX callx4
# define ARG1 a6 /* 1st outgoing call argument */
# define ARG2 a7 /* 2nd outgoing call argument */
# define ARG3 a8 /* 3rd outgoing call argument */
# define ARG4 a9 /* 4th outgoing call argument */
# define ARG5 a10 /* 5th outgoing call argument */
#endif
.text
.align 4
_start:
__start:
/*
* _start is typically NOT at the beginning of the text segment --
* it is always called from either the reset vector or other code
* that does equivalent initialization (such as crt0-app.S).
*
* Assumptions on entry to _start:
* - low (level-one) and medium priority interrupts are disabled
* via PS.INTLEVEL and/or INTENABLE (PS.INTLEVEL is expected to
* be zeroed, to potentially enable them, before calling main)
* - C calling context not initialized:
* - PS not initialized
* - SP not initialized
* - the following are initialized:
* - LITBASE, cache attributes, WindowBase, WindowStart,
* CPENABLE, FP's FCR and FSR, EXCSAVE[n]
* Keep a0 zero. It is used to initialize a few things.
* It is also the return address, where zero indicates
* that the frame used by _start is the bottommost frame.
*
*/
/* not needed for Xtensa TX */
#if !XCHAL_HAVE_HALT || !XCHAL_HAVE_BOOTLOADER
movi a0, 0 /* keep this register zero. */
#endif
/*
* Initialize the stack pointer.
* See the "ABI and Software Conventions" chapter in the
* Xtensa ISA Reference manual for details.
*
* NOTE: Because the _start routine does not use any memory in its
* stack frame, and because all of its CALL instructions use a
* window size of 4, the stack frame for _start can be empty.
*/
movi sp, __stack
/*
* Now that sp (a1) is set, we can set PS as per the application (user
* vector mode, enable interrupts, enable window exceptions if
* applicable).
*/
#if XCHAL_HAVE_EXCEPTIONS
# ifdef __XTENSA_CALL0_ABI__
/* PS.WOE = 0, PS.UM = 1, PS.EXCM = 0, PS.INTLEVEL = 0 */
movi a3, PS_UM
# else
/* PS.WOE = 1, PS.UM = 1, PS.EXCM = 0, PS.INTLEVEL = 0 */
movi a3, PS_UM|PS_WOE
# endif
wsr a3, PS
rsync
#endif
/*
* Do any initialization that affects the memory map, such as
* setting up TLB entries, that needs to be done before we can
* successfully clear BSS (e.g. if some BSS segments are in
* remapped areas).
*
* NOTE: This hook works where the reset vector does not unpack
* segments (see "ROM packing" in the LSP manual), or where
* unpacking of segments is not affected by memory remapping.
* If ROM unpacking is affected, TLB setup must be done in
* assembler from the reset vector.
*
* The __memmap_init() routine can be a C function, however it
* does not have BSS initialized! In particular, __memmap_init()
* cannot set BSS variables, i.e. uninitialized global variables
* (they'll be wiped out by the following BSS clear), nor can it
* assume they are yet initialized to zero.
*
* The __memmap_init() function is optional. It is marked as a
* weak symbol, so that it gets valued zero if not defined.
*/
.weak __memmap_init
movi a4, __memmap_init
beqz a4, 1f
CALLX a4
1:
#if !XCHAL_HAVE_BOOTLOADER /* boot loader takes care of zeroing BSS */
# ifdef __XTENSA_CALL0_ABI__
/* Clear a0 again as possible CALLX to __memmap_init changed it. */
movi a0, 0
# endif
/*
* Clear the BSS (uninitialized data) segments.
* This code supports multiple zeroed sections (*.bss).
*
* Register allocation:
* a0 = 0
* a6 = pointer to start of table, and through table
* a7 = pointer to end of table
* a8 = start address of bytes to be zeroed
* a9 = end address of bytes to be zeroed
* a10 = length of bytes to be zeroed
*/
movi a6, _bss_table_start
movi a7, _bss_table_end
bgeu a6, a7, .L3zte
.L0zte: l32i a8, a6, 0 /* get start address, assumed multiple of 4 */
l32i a9, a6, 4 /* get end address, assumed multiple of 4 */
addi a6, a6, 8 /* next entry */
sub a10, a9, a8 /* a10 = length, assumed a multiple of 4 */
bbci.l a10, 2, .L1zte
s32i a0, a8, 0 /* clear 4 bytes to make len multiple of 8 */
addi a8, a8, 4
.L1zte: bbci.l a10, 3, .L2zte
s32i a0, a8, 0 /* clear 8 bytes to make len multiple of 16 */
s32i a0, a8, 4
addi a8, a8, 8
.L2zte: srli a10, a10, 4 /* len is now multiple of 16, divide by 16 */
floopnez a10, clearzte
s32i a0, a8, 0 /* clear 16 bytes at a time... */
s32i a0, a8, 4
s32i a0, a8, 8
s32i a0, a8, 12
addi a8, a8, 16
floopend a10, clearzte
bltu a6, a7, .L0zte /* loop until end of table of *.bss sections */
.L3zte:
#endif /* !XCHAL_HAVE_BOOTLOADER */
/* Enter C domain, never returns from here */
CALL _Cstart
.size _start, . - _start