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asm volatile (
        /* disable interrupts, set mode */
        "mrs     r0, cpsr \n"
        "bic     r0, r0, #0x1f \n"
        "orr     r0, r0, #0xd3 \n"
        "msr     cpsr, r0 \n"

        /* disable cache */
        "ldr     r0, =0xefff0000 \n"
        "ldrh    r1, [r0] \n"
        "strh    r1, [r0] \n"

        /* unmap */
        "mov     r0, #0x18000000 \n"
        "add     r0, r0, #0x1c000 \n"
        "mov     r1, #0 \n"
        "str     r1, [r0, #4] \n"

        /* setup stacks in iram */
        "msr     cpsr, #0xd2 \n"
        "ldr     r1, =0x18200274 \n"
        "add     r1, r1, #0x200 \n"
        "mov     sp, r1 \n"
        "msr     cpsr, #0xd3 \n"
        "add     r1, r1, #0x400 \n"
        "mov     sp, r1 \n"

        /* jump into rom main() just before call to dfu mode */
        "ldr     r0, =0xec0 \n"
        "bx      r0 \n"
    );