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Bare-Metal Firmware on Cortex-R52 - Writing a UART Driver

We have supplied a small Rust no-std application, which is designed to run inside a QEMU emulation of an Armv8-R Cortex-R52 system. We build the code using the armv8r-none-eabihf target.

The application lives in ./qemu-code/uart-driver.

The application talks to the outside world through a UART driver. We have provided two - a working one, and a template one that doesn't work which you need to fix.

Task 1 - Get UART TX working

Modify the template driver and complete the missing code sections as commented. You can peek at the complete driver if you really need to!

This will involve reading and writing to the given registers. You have been given the base-address of the UART peripheral as a const generic, and you have been given constants for the offset of each register from the base address (assuming you are working with a *mut u32).

You'll want to write a private method to read/write each register, and use write_volatile and read_volatile to access them.

Task 2 - Get UART RX working

Continue modifying the UART driver so that you can read data. You'll need to enable the RX bit in the configuration register, and add an appropriate method to read a single byte, returning Option<u8>. Now modify the main loop to echo back received characters.

You'll need to look in the Cortex-M SDK UART documentation to see which bit in the status register indicates that the 1-byte long RX FIFO has data in it.

Running the code

You will need QEMU 9 installed and in your $PATH for cargo run to work. This was the first version with Arm Cortex-R52 emulation.

With the template unfinished:

$ cargo run
   Compiling uart-exercise v0.1.0 (/Users/jonathan/Documents/ferrous-systems/rust-exercises/qemu-code/uart-driver)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.14s
     Running `qemu-system-arm -machine mps3-an536 -cpu cortex-r52 -semihosting -nographic -kernel target/armv8r-none-eabihf/debug/uart-exercise`
PANIC: PanicInfo { payload: Any { .. }, message: Some(I am a panic), location: Location { file: "src/main.rs", line: 43, col: 5 }, can_unwind: true, force_no_backtrace: false }

With the Task 1 completed:

$ cargo run
   Compiling uart-exercise v0.1.0 (/Users/jonathan/Documents/ferrous-systems/rust-exercises/qemu-code/uart-driver)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.14s
     Running `qemu-system-arm -machine mps3-an536 -cpu cortex-r52 -semihosting -nographic -kernel target/armv8r-none-eabihf/debug/uart-exercise`
Hello, this is Rust!
    1.00     2.00     3.00     4.00     5.00     6.00     7.00     8.00     9.00    10.00
    2.00     4.00     6.00     8.00    10.00    12.00    14.00    16.00    18.00    20.00
    3.00     6.00     9.00    12.00    15.00    18.00    21.00    24.00    27.00    30.00
    4.00     8.00    12.00    16.00    20.00    24.00    28.00    32.00    36.00    40.00
    5.00    10.00    15.00    20.00    25.00    30.00    35.00    40.00    45.00    50.00
    6.00    12.00    18.00    24.00    30.00    36.00    42.00    48.00    54.00    60.00
    7.00    14.00    21.00    28.00    35.00    42.00    49.00    56.00    63.00    70.00
    8.00    16.00    24.00    32.00    40.00    48.00    56.00    64.00    72.00    80.00
    9.00    18.00    27.00    36.00    45.00    54.00    63.00    72.00    81.00    90.00
   10.00    20.00    30.00    40.00    50.00    60.00    70.00    80.00    90.00   100.00
PANIC: PanicInfo { payload: Any { .. }, message: Some(I am a panic), location: Location { file: "src/main.rs", line: 43, col: 5 }, can_unwind: true, force_no_backtrace: false }