Add raw MMIO example.

src/SUMMARY.md

@@ -240,7 +240,7 @@
   - [A minimal example](bare-metal/minimal.md)
   - [alloc](bare-metal/alloc.md)
 - [Microcontrollers](bare-metal/microcontrollers.md)
-  - [Raw MMIO]()
+  - [Raw MMIO](bare-metal/microcontrollers/mmio.md)
   - [PACs](bare-metal/microcontrollers/pacs.md)
   - [HAL crates](bare-metal/microcontrollers/hals.md)
   - [Board support crates](bare-metal/microcontrollers/board-support.md)

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

@@ -16,11 +16,14 @@ panic-halt = "0.2.0"
 [[bin]]
 name = "board_support"
 
-[[bin]]
-name = "pac"
-
 [[bin]]
 name = "hal"
 
+[[bin]]
+name = "mmio"
+
+[[bin]]
+name = "pac"
+
 [[bin]]
 name = "typestate"

src/bare-metal/microcontrollers/examples/src/bin/interrupts/mod.rs

@@ -0,0 +1,17 @@
+// 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.
+
+#[link_section = ".vector_table.interrupts"]
+#[no_mangle]
+pub static __INTERRUPTS: [usize; 1] = [0];

src/bare-metal/microcontrollers/examples/src/bin/mmio.rs

@@ -0,0 +1,66 @@
+// 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: Example
+#![no_main]
+#![no_std]
+
+extern crate panic_halt as _;
+
+mod interrupts;
+
+use core::mem::size_of;
+use cortex_m_rt::entry;
+
+/// GPIO port 0 peripheral address
+const GPIO_P0: usize = 0x5000_0000;
+
+// GPIO peripheral offsets
+const PIN_CNF: usize = 0x700;
+const OUTSET: usize = 0x508;
+const OUTCLR: usize = 0x50c;
+
+// PIN_CNF fields
+const DIR_OUTPUT: u32 = 0x1;
+const INPUT_DISCONNECT: u32 = 0x1 << 1;
+const PULL_DISABLED: u32 = 0x0 << 2;
+const DRIVE_S0S1: u32 = 0x0 << 8;
+const SENSE_DISABLED: u32 = 0x0 << 16;
+
+#[entry]
+fn main() -> ! {
+    // Configure GPIO 0 pins 21 and 28 as push-pull outputs.
+    let pin_cnf_21 = (GPIO_P0 + PIN_CNF + 21 * size_of::<u32>()) as *mut u32;
+    let pin_cnf_28 = (GPIO_P0 + PIN_CNF + 28 * size_of::<u32>()) as *mut u32;
+    // Safe because the pointers are to valid peripheral control registers, and no aliases exist.
+    unsafe {
+        pin_cnf_21.write_volatile(
+            DIR_OUTPUT | INPUT_DISCONNECT | PULL_DISABLED | DRIVE_S0S1 | SENSE_DISABLED,
+        );
+        pin_cnf_28.write_volatile(
+            DIR_OUTPUT | INPUT_DISCONNECT | PULL_DISABLED | DRIVE_S0S1 | SENSE_DISABLED,
+        );
+    }
+
+    // Set pin 28 low and pin 21 high to turn the LED on.
+    let gpio0_outset = (GPIO_P0 + OUTSET) as *mut u32;
+    let gpio0_outclr = (GPIO_P0 + OUTCLR) as *mut u32;
+    // Safe because the pointers are to valid peripheral control registers, and no aliases exist.
+    unsafe {
+        gpio0_outclr.write_volatile(1 << 28);
+        gpio0_outset.write_volatile(1 << 21);
+    }
+
+    loop {}
+}

src/bare-metal/microcontrollers/mmio.md

@@ -0,0 +1,5 @@
+# Raw MMIO
+
+```rust,editable,compile_fail
+{{#include examples/src/bin/mmio.rs:Example}}
+```