diff --git a/Cargo.toml b/Cargo.toml
index 75555ed..7e7c319 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -9,6 +9,7 @@ authors = ["Jonathan 'theJPster' Pallant <neotron@thejpster.org.uk>"]
 [dependencies]
 neotron-ffi = "0.1"
 neotron-api = "0.2"
+neotron-common-bios = "0.12"
 
 [target.'cfg(unix)'.dependencies]
 crossterm = "0.26"
diff --git a/src/ioctls/gfx.rs b/src/ioctls/gfx.rs
new file mode 100644
index 0000000..5210764
--- /dev/null
+++ b/src/ioctls/gfx.rs
@@ -0,0 +1,44 @@
+//! Graphics ioctl constants
+
+/// Clear the screen
+///
+/// The corresponding value is the fill colour, which is taken modulo the number of on-screen colours.
+pub const COMMAND_CLEAR_SCREEN: u64 = 0;
+
+/// Plot a chunky pixel
+///
+/// The command contains [ x | y | mode | colour ].
+///
+/// * `x` is 16 bits and marks the horizontal position (0 is left)
+/// * `y` is 16 bits and marks the vertical position (0 is top)
+/// * `mode` is 8 bits and is currently ignored
+/// * `colour` is 24 bits, and is taken modulo the number of on-screen colours
+///
+/// Use [`chunky_plot_value`] to create a suitable value for this ioctl command.
+pub const COMMAND_CHUNKY_PLOT: u64 = 1;
+
+/// Change graphics mode
+///
+/// The command contains the video mode in the upper 32 bits and a pointer to a
+/// framebuffer in the lower 32 bits.
+///
+/// The framebuffer pointer must point to a 32-bit aligned region of memory
+/// that is large enough for the selected mode. If you pass `null`, then the OS
+/// will attempt to allocate a framebuffer for you.
+///
+/// Use [`change_mode_value`] to construct a value.
+pub const COMMAND_CHANGE_MODE: u64 = 2;
+
+/// Calculate a 64-bit value argument for a gfx ioctl
+pub fn chunky_plot_value(x: u16, y: u16, colour: u32) -> u64 {
+    (x as u64) << 48 | (y as u64) << 32 | (colour & 0xFFFFFF) as u64
+}
+
+/// Calculate a 64-bit value argument for a gfx ioctl
+pub fn change_mode_value(mode: crate::VideoMode, fb_ptr: *mut u32) -> u64 {
+    let fb_ptr = fb_ptr as usize as u64;
+    let mode = mode.as_u8() as u64;
+    mode << 32 | fb_ptr
+}
+
+// End of file
diff --git a/src/ioctls/mod.rs b/src/ioctls/mod.rs
new file mode 100644
index 0000000..9379d18
--- /dev/null
+++ b/src/ioctls/mod.rs
@@ -0,0 +1,3 @@
+//! A collection of ioctl constants
+
+pub mod gfx;
diff --git a/src/lib.rs b/src/lib.rs
index 5aa1943..b85e30f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -27,10 +27,14 @@ pub use neotron_ffi::{FfiBuffer, FfiByteSlice, FfiString};
 
 pub use neotron_api::{file::Flags, path, Api, Error};
 
+pub use neotron_common_bios::video::Mode as VideoMode;
+
 use neotron_api as api;
 
 pub mod console;
 
+pub mod ioctls;
+
 #[cfg(not(target_os = "none"))]
 mod fake_os_api;
 
@@ -204,8 +208,14 @@ impl File {
 
     /// Perform a special I/O control operation.
     ///
-    /// The allowed values of `command` and `value` are TBD.
-    pub fn ioctl(&self, command: u64, value: u64) -> Result<u64> {
+    /// The allowed values of `command` and `value` are defined in the
+    /// [`ioctls`] module.
+    ///
+    /// # Safety
+    ///
+    /// Refer to the documentation for the ioctl you are using. Raw pointers may
+    /// be involved.
+    pub unsafe fn ioctl(&self, command: u64, value: u64) -> Result<u64> {
         let api = get_api();
         match (api.ioctl)(self.0, command, value) {
             neotron_ffi::FfiResult::Ok(output) => Ok(output),