Static FCB_BUFFER

#[no_mangle]
#[link_section = ".fcb_buffer"]
pub(crate) static mut FCB_BUFFER: [u8; 3584]

Buffer between FCB and IVT

The FCB is put at the start of flash. We then need to add a 4K buffer in between the start of flash to the IVT. This buffer provides that padding.

See justification for the ".stack_buffer" section to understand why we need explicit padding for the FCB.