I guess this is more of a question than an issue but I've found that the rpi4 doesnt produce the expected result when using atomic operations.

So, I have 2 atomic operations lined up one after the other. I'd have expected an Ok(1) after the compare and swap.

 info!("kernel_state: {:?}", state::state_manager().0.load(Ordering::Acquire));
 info!("compare and swap {:?}", state::state_manager().0
 .compare_exchange(
 state::StateManager::INIT,
 state::StateManager::SINGLE_CORE_MAIN,
 Ordering::Acquire,
 Ordering::Relaxed,
 ));

but instead I get an error.

[ 0.481485] kernel_state: 0
[ 0.484178] compare and swap Err(1)

Question:
The MMU is disabled. I'm not familiar with atomic instructions but for atomic operations to work on the rpi4, must the MMU be enabled. Is this correct? I was going to test this by enabling the MMU but just wanted to check before I head down this road.

Note:

• rust playground gives me the expected result