Add separate binary for minimal UART driver.

src/bare-metal/aps/better-uart/using.md

@@ -4,5 +4,5 @@ Let's write a small program using our driver to write to the serial console, and
 bytes.
 
 ```rust,editable,compile_fail
-{{#include ../examples/src/main.rs:main}}
+{{#include ../examples/src/main_improved.rs:main}}
 ```

src/bare-metal/aps/examples/Cargo.toml

@@ -13,3 +13,11 @@ spin = "0.9.4"
 
 [build-dependencies]
 cc = "1.0.73"
+
+[[bin]]
+name = "minimal"
+path = "src/main_minimal.rs"
+
+[[bin]]
+name = "improved"
+path = "src/main_improved.rs"

src/bare-metal/aps/examples/Makefile

@@ -17,8 +17,16 @@
 build:
 	cargo build
 
-ap-examples.bin: build
-	aarch64-linux-gnu-objcopy -O binary target/aarch64-unknown-none/debug/ap-examples ap-examples.bin
+minimal.bin: build
+	aarch64-linux-gnu-objcopy -O binary target/aarch64-unknown-none/debug/minimal minimal.bin
+improved.bin: build
+	aarch64-linux-gnu-objcopy -O binary target/aarch64-unknown-none/debug/improved improved.bin
 
-qemu: ap-examples.bin
-	qemu-system-aarch64 -machine virt -cpu max -serial mon:stdio -display none -kernel ap-examples.bin -s
+qemu_minimal: minimal.bin
+	qemu-system-aarch64 -machine virt -cpu max -serial mon:stdio -display none -kernel minimal.bin -s
+qemu: improved.bin
+	qemu-system-aarch64 -machine virt -cpu max -serial mon:stdio -display none -kernel improved.bin -s
+
+clean:
+	cargo clean
+	rm -f *.bin

src/bare-metal/aps/examples/src/main_improved.rs

@@ -18,7 +18,6 @@
 
 mod exceptions;
 mod pl011;
-mod pl011_minimal;
 
 use crate::pl011::Uart;
 use core::{fmt::Write, panic::PanicInfo};

src/bare-metal/aps/examples/src/main_minimal.rs

@@ -0,0 +1,47 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// ANCHOR: main
+#![no_main]
+#![no_std]
+
+mod exceptions;
+mod pl011_minimal;
+
+use crate::pl011_minimal::Uart;
+use core::{fmt::Write, panic::PanicInfo};
+use log::error;
+use psci::system_off;
+
+/// Base address of the primary PL011 UART.
+pub const PL011_BASE_ADDRESS: usize = 0x900_0000;
+
+#[no_mangle]
+extern "C" fn main(x0: u64, x1: u64, x2: u64, x3: u64) {
+    // Safe because `PL011_BASE_ADDRESS` is the base address of a PL011 device,
+    // and nothing else accesses that address range.
+    let mut uart = unsafe { Uart::new(PL011_BASE_ADDRESS) };
+
+    writeln!(uart, "main({:#x}, {:#x}, {:#x}, {:#x})", x0, x1, x2, x3).unwrap();
+
+    system_off().unwrap();
+}
+// ANCHOR_END: main
+
+#[panic_handler]
+fn panic(info: &PanicInfo) -> ! {
+    error!("{}", info);
+    system_off().unwrap();
+    loop {}
+}