Driver

Now let's use the new Registers struct in our driver.

# // Copyright 2025 Google LLC
# // SPDX-License-Identifier: Apache-2.0
#
{{#include ../examples/src/pl011.rs:Uart}}

• The driver no longer needs any unsafe code!
• UniqueMmioPointer is a wrapper around a raw pointer to an MMIO device or register. The caller of UniqueMmioPointer::new promises that it is valid and unique for the given lifetime, so it can provide safe methods to read and write fields.
• Note that Uart::new is now safe; UniqueMmioPointer::new is unsafe instead.
• These MMIO accesses are generally a wrapper around read_volatile and write_volatile, though on aarch64 they are instead implemented in assembly to work around a bug where the compiler can emit instructions that prevent MMIO virtualization.
• The field! and field_shared! macros internally use &raw mut and &raw const to get pointers to individual fields without creating an intermediate reference, which would be unsound.
• field! needs a mutable reference to a UniqueMmioPointer, and returns a UniqueMmioPointer that allows reads with side effects and writes.
• field_shared! works with a shared reference to either a UniqueMmioPointer or a SharedMmioPointer. It returns a SharedMmioPointer that only allows pure reads.