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trezor-firmware/core/embed/bootloader/startup_stm32f4.s

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.syntax unified
.text
.global reset_handler
.type reset_handler, STT_FUNC
reset_handler:
// setup environment for subsequent stage of code
ldr r0, =ccmram_start // r0 - point to beginning of CCMRAM
ldr r1, =ccmram_end // r1 - point to byte where BOOT_ARGS region starts
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ldr r2, =0 // r2 - the word-sized value to be written
bl memset_reg
ldr r0, =sram_start // r0 - point to beginning of SRAM
ldr r1, =sram_end // r1 - point to byte after the end of SRAM
ldr r2, =0 // r2 - the word-sized value to be written
bl memset_reg
// copy data in from flash
ldr r0, =data_vma // dst addr
ldr r1, =data_lma // src addr
ldr r2, =data_size // size in bytes
bl memcpy
// setup the stack protector (see build script "-fstack-protector-all") with an unpredictable value
bl rng_get
ldr r1, = __stack_chk_guard
str r0, [r1]
// re-enable exceptions
// according to "ARM Cortex-M Programming Guide to Memory Barrier Instructions" Application Note 321, section 4.7:
// "If it is not necessary to ensure that a pended interrupt is recognized immediately before
// subsequent operations, it is not necessary to insert a memory barrier instruction."
cpsie f
// r11 contains the command passed to bootargs_set()
// function called when the firmware rebooted to the bootloader
ldr r0, =g_boot_command_shadow
str r11, [r0]
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// enter the application code
bl main
b shutdown_privileged
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.end