I haven't tested this because my atmega2560 is currently soldered and…

… doesn't have the right pins. Will fix that soon. If someone else can test would be great.

examples/atmega2560/src/bin/atmega2560-usart_spi-feedback.rs

@@ -0,0 +1,58 @@
+//! This example demonstrates how to set up a SPI interface and communicate
+//! over it.  The physical hardware configuration consists of connecting a
+//! jumper directly from pin `PB2` to pin `PB3`.
+//!
+//! Run the program using `cargo run`.
+//! You should see it output the line `data: 42` repeatedly.
+//! If the output you see is `data: 255`, you may need to check your jumper.
+
+#![no_std]
+#![no_main]
+
+use atmega_hal::delay::Delay;
+use atmega_hal::usart::{Baudrate, Usart};
+use atmega_hal::usart_spi;
+use embedded_hal::delay::DelayNs;
+use embedded_hal::spi::SpiBus;
+use panic_halt as _;
+
+// Define core clock. This can be used in the rest of the project.
+type CoreClock = atmega_hal::clock::MHz16;
+
+#[avr_device::entry]
+fn main() -> ! {
+    let dp = atmega_hal::Peripherals::take().unwrap();
+    let pins = atmega_hal::pins!(dp);
+
+    let mut delay = Delay::<crate::CoreClock>::new();
+
+    // set up serial interface for text output
+    let mut serial = Usart::new(
+        dp.USART0,
+        pins.pe0,
+        pins.pe1.into_output(),
+        Baudrate::<crate::CoreClock>::new(57600),
+    );
+
+    // Create SPI interface.
+    let (mut spi, _) = usart_spi::Usart1Spi::new(
+        dp.SPI,
+        pins.pd5.into_output(),
+        pins.pd3.into_output(),
+        pins.pd2.into_pull_up_input(),
+        pins.pd4.into_output().downgrade(),
+        spi::Settings::default(),
+    );
+
+    loop {
+        // Send a byte
+        let data_out: [u8; 1] = [42];
+        let mut data_in: [u8; 1] = [0];
+        // Send a byte
+        // Because MISO is connected to MOSI, the read data should be the same
+        spi.transfer(&mut data_in, &data_out).unwrap();
+
+        ufmt::uwriteln!(&mut serial, "data: {}\r", data_in[0]).unwrap();
+        delay.delay_ms(1000);
+    }
+}