.syntax unified
.cpu cortex-m0plus
.thumb

.global  boot2_pre

.section  .text.boot2_pre
.type  boot2_pre, %function
boot2_pre:
    cpsid i

/* clear bss section */
    ldr r0, =0
    ldr r1, =_bss_start
    ldr r2, =_bss_end
    cmp r1, r2
    bhs 2f
1:
    str r0, [r1]
    adds r1, r1, #4
    cmp r1, r2
    blo 1b
2:

    ldr r0, =_stack_top
    msr msp, r0
    bl boot2_copy_self
    bl main
    b .

.size  .boot2_pre, .-boot2_pre