asm::delay() only blocks half the time intended on an STM32H7

The asm::delay() function delays a program only by half the time/CPU cycles intended on an STM32H7.
I have prepared a somewhat minimal example here. My CPU clock is at 400 MHz and I specify a delay of 4_000_000_000 cycles which should lead to a 10 second delay. The actual delay is 5 seconds for me.

I have also confirmed the same behavior in other programs on an STM32H7 with much shorter timescales and looking at IOs on a scope. The delay is always exactly half the time expected.

One guess is that this is due to the dual issue pipeline of the H7 eating up two instructions per cycle.

Start with src/asm.rs, especially the asm::delay() implementation, and reproduce the behavior using the linked minimal example in src/main.rs on an STM32H7. Compare the requested cycle count with the observed delay and determine whether the implementation accounts for the H7's execution behavior. Done means a 4,000,000,000-cycle delay produces the intended 10-second delay.