Generating a random number in ARM assembly with Raspberry Pi

I'm currently working on an assembly project right now and I have to generate a random number. So far I've managed to write some code that should work, but I don't think is working beacuse it does not print the random number. My code is this:

/*--random01.s*/
.data

.balign 4
mensaje1: .asciz "Random \n"

.balign 4
return: .word 0

.text

.global main
main:

    ldr r1, addr_of_return
    str lr, [r1]

    ldr r0, addr_of_msg1
    bl printf

    tst r1,r1, lsr #1
    movs r2,r0, rrx
    adc r1,r1, r1
    eor r2,r2, r0, lsl #12
    eor r0,r2, r2, lsr #20

    ldr r0, [r0]
    bl printf

    ldr lr, addr_of_return
    ldr lr, [lr]
    bx lr

addr_of_msg1: .word mensaje1
addr_of_return: .word return

.global printf

My question is, how can I achieve the generation of a random number? Am I doing this right or should I try working with the clock?