Add `os` module for querying OS and hardware state

Most of these are dead simple and don't require any service
initialization etc., so all we need is a simple wrapper. I didn't
implement everything in <3ds/os.h> yet, but got most of the basic ones
which seemed like likely use cases to me.

ctru-rs/src/error.rs

@@ -152,6 +152,8 @@ impl fmt::Debug for Error {
 impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {
+            // TODO: should we consider using ctru_sys::osStrError here as well?
+            // It might do some of the work for us or provide additional details
             &Self::Os(err) => write!(
                 f,
                 "libctru result code 0x{err:08X}: [{} {}] {}: {}",

ctru-rs/src/lib.rs

@@ -107,6 +107,7 @@ pub mod console;
 pub mod error;
 pub mod linear;
 pub mod mii;
+pub mod os;
 pub mod prelude;
 pub mod services;
 

ctru-rs/src/os.rs

@@ -0,0 +1,135 @@
+//! Utilities to get information about the operating system and hardware state.
+
+/// System version information.
+#[derive(Clone, Copy)]
+pub struct Version(u32);
+
+impl Version {
+    /// Pack a system version from its components
+    pub fn new(major: u8, minor: u8, revision: u8) -> Self {
+        let major = u32::from(major);
+        let minor = u32::from(minor);
+        let revision = u32::from(revision);
+
+        Self(major << 24 | minor << 16 | revision << 8)
+    }
+
+    /// Get the major version from a packed system version.
+    pub fn major(&self) -> u8 {
+        (self.0 >> 24).try_into().unwrap()
+    }
+
+    /// Get the minor version from a packed system version.
+    pub fn minor(&self) -> u8 {
+        (self.0 >> 16 & 0xFF).try_into().unwrap()
+    }
+
+    /// Get the revision from a packed system version.
+    pub fn revision(&self) -> u8 {
+        (self.0 >> 8 & 0xFF).try_into().unwrap()
+    }
+}
+
+/// Get the system's FIRM version.
+pub fn firm_version() -> Version {
+    Version(unsafe { ctru_sys::osGetFirmVersion() })
+}
+
+/// Get the system's kernel version.
+pub fn kernel_version() -> Version {
+    Version(unsafe { ctru_sys::osGetKernelVersion() })
+}
+
+// TODO: I can't seem to find good documentation on it, but we could probably
+// define enums for firmware type (NATIVE_FIRM, SAFE_FIRM etc.) as well as
+// application memory layout. Leaving those as future enhancements for now
+
+/// A region of memory. Most applications will only use [`Application`](MemRegion::Application)
+/// memory, but the other types can be used to query memory usage information.
+/// See <https://www.3dbrew.org/wiki/Memory_layout#FCRAM_memory-regions_layout>
+/// for more details on the different types of memory.
+///
+/// # Example
+/// ```
+/// # let _runner = test_runner::GdbRunner::default();
+/// let all_memory = ctru::os::MemRegion::All;
+///
+/// assert!(all_memory.size() > 0);
+/// assert!(all_memory.used() > 0);
+/// assert!(all_memory.free() > 0);
+/// ```
+#[derive(Clone, Copy, Debug)]
+#[non_exhaustive]
+#[repr(u32)]
+pub enum MemRegion {
+    /// All memory regions.
+    All = ctru_sys::MEMREGION_ALL,
+    /// APPLICATION memory.
+    Application = ctru_sys::MEMREGION_APPLICATION,
+    /// SYSTEM memory.
+    System = ctru_sys::MEMREGION_SYSTEM,
+    /// BASE memory.
+    Base = ctru_sys::MEMREGION_BASE,
+}
+
+impl MemRegion {
+    /// Get the total size of this memory region, in bytes.
+    pub fn size(&self) -> usize {
+        unsafe { ctru_sys::osGetMemRegionSize(*self as u32) }
+            .try_into()
+            .unwrap()
+    }
+
+    /// Get the number of bytes used within this memory region.
+    pub fn used(&self) -> usize {
+        unsafe { ctru_sys::osGetMemRegionUsed(*self as u32) }
+            .try_into()
+            .unwrap()
+    }
+
+    /// Get the number of bytes free within this memory region.
+    pub fn free(&self) -> usize {
+        unsafe { ctru_sys::osGetMemRegionFree(*self as u32) }
+            .try_into()
+            .unwrap()
+    }
+}
+
+/// WiFi signal strength. This enum's [`u8`] representation corresponds with
+/// the number of bars displayed in the Home menu.
+#[non_exhaustive]
+#[repr(u8)]
+pub enum WifiStrength {
+    /// This may indicate a very poor signal quality even worse than `Bad`,
+    /// or it may indicate that no network is connected at all.
+    Disconnected = 0,
+    /// Poor signal strength.
+    Bad = 1,
+    /// Medium signal strength.
+    Decent = 2,
+    /// Good signal strength.
+    Good = 3,
+}
+
+impl WifiStrength {
+    /// Get the current WiFi signal strength.
+    pub fn current() -> Self {
+        match unsafe { ctru_sys::osGetWifiStrength() } {
+            0 => Self::Disconnected,
+            1 => Self::Bad,
+            2 => Self::Decent,
+            3 => Self::Good,
+            other => panic!("Got unexpected WiFi strength value {other}"),
+        }
+    }
+}
+
+/// Get the current value of the stereoscopic 3D slider on a scale from 0.0­–­1.0.
+pub fn current_3d_slider_state() -> f32 {
+    unsafe { ctru_sys::osGet3DSliderState() }
+}
+
+/// Whether or not a headset is currently plugged into the device.
+pub fn is_headset_connected() -> bool {
+    unsafe { ctru_sys::osIsHeadsetConnected() }
+}