Module f3::examples::itm

With the iprint! macros you can send print!-formatted messages to the HOST

Where the HOST is the machine, likely your laptop, that's debugging the F3 using OpenOCD+GDB.

To receive the messages on the HOST you can use the itmdump tool to parse the "instrumentation packets" that the F3 will send:

$ cargo install itm

itmdump uses a named pipe to receive the data that the F3 sends. Call itmdump like this to create and use a named pipe in the /tmp directory:

$ itmdump /tmp/itm.fifo

The command will block, let it be. Next, configure OpenOCD to send the F3 messages to the named pipe that you just created. You can do this from your current GDB session:

(gdb) monitor tpiu config internal /tmp/itm.fifo uart off 8000000

(The above command assumes your F3 is running at 8MHz, which is the default clock frequency)

After that, the output of every iprint! call will appear in itmdump stdout! Note that if itmdump is connected to a terminal, its output will be line buffered so won't see anything printed on screen until a newline (\n) is reached. The example below, produces the following output.

$ itmdump /tmp/itm.fifo
Hello, world!

Notes

You'll have to enter that monitor command on each GDB session so it's a good idea to add it to your .gdbinit so it gets done automatically when GDB starts.

OTOH, You don't have to spawn a new itmdump command for each debug session. The same process will continue to work for all subsequent debug sessions as long as you don't exit it (e.g. with Ctrl+C).

#![no_main]
#![no_std]

#[macro_use]
extern crate f3;

#[export_name = "main"]
pub fn main() -> ! {
    iprintln!("Hello, world!");

    loop {}
}