Baking Pi OK05 - Why "ldr" twice to make the pattern work?

Question

I'm carefully following Baking Pi with my model B, making sure I fully understand everything going on. I am now at lesson 5, to flash the SOS Morse code. It works fine, but I am curious why it needs two ldr instructions to load the pattern. (Link to the site)

The data section defines:

.align 2
pattern:
    .int 0b11111111101010100010001000101010

And this pattern is loaded into register r4 (.req ptrn) by:

ptrn .req r4
ldr ptrn,=pattern
ldr ptrn,[ptrn]

So why the double ldr?

I tried without the second one, but that screws up the pattern. Does it have to do with the alignment? I thought the first Load Register would be enough to load the value.

Thanks :)

Answer 1

Okay, I figured it out myself...

The first ldr actually loads the address of the variable. And so to have the value of pattern in the register (rather than the address), I still have to load the value at the address into the register.

Also check here