examples: add a example of using GPIO to light up LED

Signed-off-by: zhujunxing <zjx1319@hust.edu.cn>

Author: jakezhu9

Cargo.lock

@@ -6,6 +6,7 @@ members = [
     "sophgo-rom-rt/macros",
     "sophgo-rom-tool",
     "examples/hello-world",
+    "examples/blinky",
 ]
 
 [workspace.package]

Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "blinky"
+version = "0.0.0"
+
+edition.workspace = true
+license.workspace = true
+repository.workspace = true
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+sophgo-rom-rt = { version = "0.0.0", path = "../../sophgo-rom-rt" }
+panic-halt = "0.2.0"
+
+[[bin]]
+name = "blinky"
+test = false
+bench = false

examples/blinky/Cargo.toml

@@ -0,0 +1,3 @@
+fn main() {
+    println!("cargo:rustc-link-arg=-Tsophgo-rom-rt.ld");
+}

examples/blinky/build.rs

@@ -0,0 +1,33 @@
+// rustup target install riscv64imac-unknown-none-elf
+// cargo build -p blinky --target riscv64imac-unknown-none-elf --release
+
+#![no_std]
+#![no_main]
+
+use core::arch::asm;
+
+use panic_halt as _;
+use sophgo_rom_rt::{entry, Peripherals};
+
+#[entry]
+fn main(p: Peripherals) -> ! {
+    unsafe {
+        p.rtc_gpio
+            .direction
+            .write(p.rtc_gpio.direction.read().set_output(2));
+    }
+    loop {
+        unsafe {
+            p.rtc_gpio.data.write(p.rtc_gpio.data.read() | (1 << 2));
+        }
+        for _ in 0..=1_000_000 {
+            unsafe { asm!("nop") };
+        }
+        unsafe {
+            p.rtc_gpio.data.write(p.rtc_gpio.data.read() & !(1 << 2));
+        }
+        for _ in 0..=1_000_000 {
+            unsafe { asm!("nop") };
+        }
+    }
+}