diff --git a/sim/src/area.rs b/sim/src/area.rs
new file mode 100644
index 0000000..9bb7d57
--- /dev/null
+++ b/sim/src/area.rs
@@ -0,0 +1,161 @@
+//! Describe flash areas.
+
+use flash::{Flash, Sector};
+use std::marker::PhantomData;
+use std::ptr;
+
+/// Structure to build up the boot area table.
+#[derive(Debug)]
+pub struct AreaDesc {
+    areas: Vec<Vec<FlashArea>>,
+    whole: Vec<FlashArea>,
+    sectors: Vec<Sector>,
+}
+
+impl AreaDesc {
+    pub fn new(flash: &Flash) -> AreaDesc {
+        AreaDesc {
+            areas: vec![],
+            whole: vec![],
+            sectors: flash.sector_iter().collect(),
+        }
+    }
+
+    /// Add a slot to the image.  The slot must align with erasable units in the flash device.
+    /// Panics if the description is not valid.  There are also bootloader assumptions that the
+    /// slots are SLOT0, SLOT1, and SCRATCH in that order.
+    pub fn add_image(&mut self, base: usize, len: usize, id: FlashId) {
+        let nid = id as usize;
+        let orig_base = base;
+        let orig_len = len;
+        let mut base = base;
+        let mut len = len;
+
+        while nid > self.areas.len() {
+            self.areas.push(vec![]);
+            self.whole.push(Default::default());
+        }
+
+        if nid != self.areas.len() {
+            panic!("Flash areas not added in order");
+        }
+
+        let mut area = vec![];
+
+        for sector in &self.sectors {
+            if len == 0 {
+                break;
+            };
+            if base > sector.base + sector.size - 1 {
+                continue;
+            }
+            if sector.base != base {
+                panic!("Image does not start on a sector boundary");
+            }
+
+            area.push(FlashArea {
+                flash_id: id,
+                device_id: 42,
+                pad16: 0,
+                off: sector.base as u32,
+                size: sector.size as u32,
+            });
+
+            base += sector.size;
+            len -= sector.size;
+        }
+
+        if len != 0 {
+            panic!("Image goes past end of device");
+        }
+
+        self.areas.push(area);
+        self.whole.push(FlashArea {
+            flash_id: id,
+            device_id: 42,
+            pad16: 0,
+            off: orig_base as u32,
+            size: orig_len as u32,
+        });
+    }
+
+    pub fn get_c(&self) -> CAreaDesc {
+        let mut areas: CAreaDesc = Default::default();
+
+        assert_eq!(self.areas.len(), self.whole.len());
+
+        for (i, area) in self.areas.iter().enumerate() {
+            if area.len() > 0 {
+                areas.slots[i].areas = &area[0];
+                areas.slots[i].whole = self.whole[i].clone();
+                areas.slots[i].num_areas = area.len() as u32;
+                areas.slots[i].id = area[0].flash_id;
+            }
+        }
+
+        areas.num_slots = self.areas.len() as u32;
+
+        areas
+    }
+}
+
+/// The area descriptor, C format.
+#[repr(C)]
+#[derive(Debug, Default)]
+pub struct CAreaDesc<'a> {
+    slots: [CArea<'a>; 16],
+    num_slots: u32,
+}
+
+#[repr(C)]
+#[derive(Debug)]
+pub struct CArea<'a> {
+    whole: FlashArea,
+    areas: *const FlashArea,
+    num_areas: u32,
+    id: FlashId,
+    phantom: PhantomData<&'a AreaDesc>,
+}
+
+impl<'a> Default for CArea<'a> {
+    fn default() -> CArea<'a> {
+        CArea {
+            areas: ptr::null(),
+            whole: Default::default(),
+            id: FlashId::BootLoader,
+            num_areas: 0,
+            phantom: PhantomData,
+        }
+    }
+}
+
+/// Flash area map.
+#[repr(u8)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+#[allow(dead_code)]
+pub enum FlashId {
+    BootLoader = 0,
+    Image0 = 1,
+    Image1 = 2,
+    ImageScratch = 3,
+    Nffs = 4,
+    Core = 5,
+    RebootLog = 6
+}
+
+impl Default for FlashId {
+    fn default() -> FlashId {
+        FlashId::BootLoader
+    }
+}
+
+#[repr(C)]
+#[derive(Debug, Clone, Default)]
+pub struct FlashArea {
+    flash_id: FlashId,
+    device_id: u8,
+    pad16: u16,
+    off: u32,
+    size: u32,
+}
+