diff --git a/sim/src/image.rs b/sim/src/image.rs
index c95d110..9a6aaed 100644
--- a/sim/src/image.rs
+++ b/sim/src/image.rs
@@ -16,12 +16,26 @@
     },
 };
 
-use simflash::{Flash, SimFlashMap};
-use mcuboot_sys::{c, AreaDesc};
+use simflash::{Flash, SimFlash, SimFlashMap};
+use mcuboot_sys::{c, AreaDesc, FlashId};
+use crate::{
+    ALL_DEVICES,
+    DeviceName,
+};
 use crate::caps::Caps;
 use crate::suit::SuitManifestGenerator;
 use crate::tlv::{ManifestGen, TlvGen, TlvFlags, AES_SEC_KEY};
 
+/// A builder for Images.  This describes a single run of the simulator,
+/// capturing the configuration of a particular set of devices, including
+/// the flash simulator(s) and the information about the slots.
+#[derive(Clone)]
+pub struct ImagesBuilder {
+    flashmap: SimFlashMap,
+    areadesc: AreaDesc,
+    slots: [SlotInfo; 2],
+}
+
 /// Images represents the state of a simulation for a given set of images.
 /// The flashmap holds the state of the simulated flash, whereas primaries
 /// and upgrades hold the expected contents of these images.
@@ -34,6 +48,188 @@
     pub total_count: Option<i32>,
 }
 
+impl ImagesBuilder {
+    pub fn new(device: DeviceName, align: u8, erased_val: u8) -> Self {
+        let (flashmap, areadesc) = Self::make_device(device, align, erased_val);
+
+        let (slot0_base, slot0_len, slot0_dev_id) = areadesc.find(FlashId::Image0);
+        let (slot1_base, slot1_len, slot1_dev_id) = areadesc.find(FlashId::Image1);
+
+        // NOTE: not accounting "swap_size" because it is not used by sim...
+        let offset_from_end = c::boot_magic_sz() + c::boot_max_align() * 2;
+
+        // Construct a primary image.
+        let slot0 = SlotInfo {
+            base_off: slot0_base as usize,
+            trailer_off: slot0_base + slot0_len - offset_from_end,
+            len: slot0_len as usize,
+            dev_id: slot0_dev_id,
+        };
+
+        // And an upgrade image.
+        let slot1 = SlotInfo {
+            base_off: slot1_base as usize,
+            trailer_off: slot1_base + slot1_len - offset_from_end,
+            len: slot1_len as usize,
+            dev_id: slot1_dev_id,
+        };
+
+        ImagesBuilder {
+            flashmap: flashmap,
+            areadesc: areadesc,
+            slots: [slot0, slot1],
+        }
+    }
+
+    pub fn each_device<F>(f: F)
+        where F: Fn(Self)
+    {
+        for &dev in ALL_DEVICES {
+            for &align in &[1, 2, 4, 8] {
+                for &erased_val in &[0, 0xff] {
+                    let run = Self::new(dev, align, erased_val);
+                    f(run);
+                }
+            }
+        }
+    }
+
+    /// Construct an `Images` that doesn't expect an upgrade to happen.
+    pub fn make_no_upgrade_image(self) -> Images {
+        let mut flashmap = self.flashmap;
+        let primaries = install_image(&mut flashmap, &self.slots, 0, 32784, false);
+        let upgrades = install_image(&mut flashmap, &self.slots, 1, 41928, false);
+        Images {
+            flashmap: flashmap,
+            areadesc: self.areadesc,
+            slots: self.slots,
+            primaries: primaries,
+            upgrades: upgrades,
+            total_count: None,
+        }
+    }
+
+    /// Construct an `Images` for normal testing.
+    pub fn make_image(self) -> Images {
+        let mut images = self.make_no_upgrade_image();
+        mark_upgrade(&mut images.flashmap, &images.slots[1]);
+
+        // upgrades without fails, counts number of flash operations
+        let total_count = match images.run_basic_upgrade() {
+            Ok(v)  => v,
+            Err(_) => {
+                panic!("Unable to perform basic upgrade");
+            },
+        };
+
+        images.total_count = Some(total_count);
+        images
+    }
+
+    pub fn make_bad_slot1_image(self) -> Images {
+        let mut bad_flashmap = self.flashmap;
+        let primaries = install_image(&mut bad_flashmap, &self.slots, 0, 32784, false);
+        let upgrades = install_image(&mut bad_flashmap, &self.slots, 1, 41928, true);
+        Images {
+            flashmap: bad_flashmap,
+            areadesc: self.areadesc,
+            slots: self.slots,
+            primaries: primaries,
+            upgrades: upgrades,
+            total_count: None,
+        }
+    }
+
+    /// Build the Flash and area descriptor for a given device.
+    pub fn make_device(device: DeviceName, align: u8, erased_val: u8) -> (SimFlashMap, AreaDesc) {
+        match device {
+            DeviceName::Stm32f4 => {
+                // STM style flash.  Large sectors, with a large scratch area.
+                let flash = SimFlash::new(vec![16 * 1024, 16 * 1024, 16 * 1024, 16 * 1024,
+                                          64 * 1024,
+                                          128 * 1024, 128 * 1024, 128 * 1024],
+                                          align as usize, erased_val);
+                let dev_id = 0;
+                let mut areadesc = AreaDesc::new();
+                areadesc.add_flash_sectors(dev_id, &flash);
+                areadesc.add_image(0x020000, 0x020000, FlashId::Image0, dev_id);
+                areadesc.add_image(0x040000, 0x020000, FlashId::Image1, dev_id);
+                areadesc.add_image(0x060000, 0x020000, FlashId::ImageScratch, dev_id);
+
+                let mut flashmap = SimFlashMap::new();
+                flashmap.insert(dev_id, flash);
+                (flashmap, areadesc)
+            }
+            DeviceName::K64f => {
+                // NXP style flash.  Small sectors, one small sector for scratch.
+                let flash = SimFlash::new(vec![4096; 128], align as usize, erased_val);
+
+                let dev_id = 0;
+                let mut areadesc = AreaDesc::new();
+                areadesc.add_flash_sectors(dev_id, &flash);
+                areadesc.add_image(0x020000, 0x020000, FlashId::Image0, dev_id);
+                areadesc.add_image(0x040000, 0x020000, FlashId::Image1, dev_id);
+                areadesc.add_image(0x060000, 0x001000, FlashId::ImageScratch, dev_id);
+
+                let mut flashmap = SimFlashMap::new();
+                flashmap.insert(dev_id, flash);
+                (flashmap, areadesc)
+            }
+            DeviceName::K64fBig => {
+                // Simulating an STM style flash on top of an NXP style flash.  Underlying flash device
+                // uses small sectors, but we tell the bootloader they are large.
+                let flash = SimFlash::new(vec![4096; 128], align as usize, erased_val);
+
+                let dev_id = 0;
+                let mut areadesc = AreaDesc::new();
+                areadesc.add_flash_sectors(dev_id, &flash);
+                areadesc.add_simple_image(0x020000, 0x020000, FlashId::Image0, dev_id);
+                areadesc.add_simple_image(0x040000, 0x020000, FlashId::Image1, dev_id);
+                areadesc.add_simple_image(0x060000, 0x020000, FlashId::ImageScratch, dev_id);
+
+                let mut flashmap = SimFlashMap::new();
+                flashmap.insert(dev_id, flash);
+                (flashmap, areadesc)
+            }
+            DeviceName::Nrf52840 => {
+                // Simulating the flash on the nrf52840 with partitions set up so that the scratch size
+                // does not divide into the image size.
+                let flash = SimFlash::new(vec![4096; 128], align as usize, erased_val);
+
+                let dev_id = 0;
+                let mut areadesc = AreaDesc::new();
+                areadesc.add_flash_sectors(dev_id, &flash);
+                areadesc.add_image(0x008000, 0x034000, FlashId::Image0, dev_id);
+                areadesc.add_image(0x03c000, 0x034000, FlashId::Image1, dev_id);
+                areadesc.add_image(0x070000, 0x00d000, FlashId::ImageScratch, dev_id);
+
+                let mut flashmap = SimFlashMap::new();
+                flashmap.insert(dev_id, flash);
+                (flashmap, areadesc)
+            }
+            DeviceName::Nrf52840SpiFlash => {
+                // Simulate nrf52840 with external SPI flash. The external SPI flash
+                // has a larger sector size so for now store scratch on that flash.
+                let flash0 = SimFlash::new(vec![4096; 128], align as usize, erased_val);
+                let flash1 = SimFlash::new(vec![8192; 64], align as usize, erased_val);
+
+                let mut areadesc = AreaDesc::new();
+                areadesc.add_flash_sectors(0, &flash0);
+                areadesc.add_flash_sectors(1, &flash1);
+
+                areadesc.add_image(0x008000, 0x068000, FlashId::Image0, 0);
+                areadesc.add_image(0x000000, 0x068000, FlashId::Image1, 1);
+                areadesc.add_image(0x068000, 0x018000, FlashId::ImageScratch, 1);
+
+                let mut flashmap = SimFlashMap::new();
+                flashmap.insert(0, flash0);
+                flashmap.insert(1, flash1);
+                (flashmap, areadesc)
+            }
+        }
+    }
+}
+
 impl Images {
     /// A simple upgrade without forced failures.
     ///
diff --git a/sim/src/lib.rs b/sim/src/lib.rs
index d001831..1fec20c 100644
--- a/sim/src/lib.rs
+++ b/sim/src/lib.rs
@@ -12,14 +12,8 @@
 mod tlv;
 pub mod testlog;
 
-use simflash::{SimFlash, SimFlashMap};
-use mcuboot_sys::{c, AreaDesc, FlashId};
-
-use crate::image::{
-    Images,
-    install_image,
-    mark_upgrade,
-    SlotInfo,
+pub use crate::image::{
+    ImagesBuilder,
     show_sizes,
 };
 
@@ -152,111 +146,6 @@
     }
 }
 
-/// A Run describes a single run of the simulator.  It captures the
-/// configuration of a particular device configuration, including the flash
-/// devices and the information about the slots.  This can be thought of as
-/// a builder for `Images`.
-#[derive(Clone)]
-pub struct Run {
-    flashmap: SimFlashMap,
-    areadesc: AreaDesc,
-    slots: [SlotInfo; 2],
-}
-
-impl Run {
-    pub fn new(device: DeviceName, align: u8, erased_val: u8) -> Run {
-        let (flashmap, areadesc) = make_device(device, align, erased_val);
-
-        let (slot0_base, slot0_len, slot0_dev_id) = areadesc.find(FlashId::Image0);
-        let (slot1_base, slot1_len, slot1_dev_id) = areadesc.find(FlashId::Image1);
-
-        // NOTE: not accounting "swap_size" because it is not used by sim...
-        let offset_from_end = c::boot_magic_sz() + c::boot_max_align() * 2;
-
-        // Construct a primary image.
-        let slot0 = SlotInfo {
-            base_off: slot0_base as usize,
-            trailer_off: slot0_base + slot0_len - offset_from_end,
-            len: slot0_len as usize,
-            dev_id: slot0_dev_id,
-        };
-
-        // And an upgrade image.
-        let slot1 = SlotInfo {
-            base_off: slot1_base as usize,
-            trailer_off: slot1_base + slot1_len - offset_from_end,
-            len: slot1_len as usize,
-            dev_id: slot1_dev_id,
-        };
-
-        Run {
-            flashmap: flashmap,
-            areadesc: areadesc,
-            slots: [slot0, slot1],
-        }
-    }
-
-    pub fn each_device<F>(f: F)
-        where F: Fn(Run)
-    {
-        for &dev in ALL_DEVICES {
-            for &align in &[1, 2, 4, 8] {
-                for &erased_val in &[0, 0xff] {
-                    let run = Run::new(dev, align, erased_val);
-                    f(run);
-                }
-            }
-        }
-    }
-
-    /// Construct an `Images` that doesn't expect an upgrade to happen.
-    pub fn make_no_upgrade_image(self) -> Images {
-        let mut flashmap = self.flashmap;
-        let primaries = install_image(&mut flashmap, &self.slots, 0, 32784, false);
-        let upgrades = install_image(&mut flashmap, &self.slots, 1, 41928, false);
-        Images {
-            flashmap: flashmap,
-            areadesc: self.areadesc,
-            slots: self.slots,
-            primaries: primaries,
-            upgrades: upgrades,
-            total_count: None,
-        }
-    }
-
-    /// Construct an `Images` for normal testing.
-    pub fn make_image(self) -> Images {
-        let mut images = self.make_no_upgrade_image();
-        mark_upgrade(&mut images.flashmap, &images.slots[1]);
-
-        // upgrades without fails, counts number of flash operations
-        let total_count = match images.run_basic_upgrade() {
-            Ok(v)  => v,
-            Err(_) => {
-                panic!("Unable to perform basic upgrade");
-            },
-        };
-
-        images.total_count = Some(total_count);
-        images
-    }
-
-    pub fn make_bad_slot1_image(self) -> Images {
-        let mut bad_flashmap = self.flashmap;
-        let primaries = install_image(&mut bad_flashmap, &self.slots, 0, 32784, false);
-        let upgrades = install_image(&mut bad_flashmap, &self.slots, 1, 41928, true);
-        Images {
-            flashmap: bad_flashmap,
-            areadesc: self.areadesc,
-            slots: self.slots,
-            primaries: primaries,
-            upgrades: upgrades,
-            total_count: None,
-        }
-    }
-
-}
-
 pub struct RunStatus {
     failures: usize,
     passes: usize,
@@ -273,7 +162,7 @@
     pub fn run_single(&mut self, device: DeviceName, align: u8, erased_val: u8) {
         warn!("Running on device {} with alignment {}", device, align);
 
-        let run = Run::new(device, align, erased_val);
+        let run = ImagesBuilder::new(device, align, erased_val);
 
         let mut failed = false;
 
@@ -311,91 +200,3 @@
     }
 }
 
-/// Build the Flash and area descriptor for a given device.
-pub fn make_device(device: DeviceName, align: u8, erased_val: u8) -> (SimFlashMap, AreaDesc) {
-    match device {
-        DeviceName::Stm32f4 => {
-            // STM style flash.  Large sectors, with a large scratch area.
-            let flash = SimFlash::new(vec![16 * 1024, 16 * 1024, 16 * 1024, 16 * 1024,
-                                      64 * 1024,
-                                      128 * 1024, 128 * 1024, 128 * 1024],
-                                      align as usize, erased_val);
-            let dev_id = 0;
-            let mut areadesc = AreaDesc::new();
-            areadesc.add_flash_sectors(dev_id, &flash);
-            areadesc.add_image(0x020000, 0x020000, FlashId::Image0, dev_id);
-            areadesc.add_image(0x040000, 0x020000, FlashId::Image1, dev_id);
-            areadesc.add_image(0x060000, 0x020000, FlashId::ImageScratch, dev_id);
-
-            let mut flashmap = SimFlashMap::new();
-            flashmap.insert(dev_id, flash);
-            (flashmap, areadesc)
-        }
-        DeviceName::K64f => {
-            // NXP style flash.  Small sectors, one small sector for scratch.
-            let flash = SimFlash::new(vec![4096; 128], align as usize, erased_val);
-
-            let dev_id = 0;
-            let mut areadesc = AreaDesc::new();
-            areadesc.add_flash_sectors(dev_id, &flash);
-            areadesc.add_image(0x020000, 0x020000, FlashId::Image0, dev_id);
-            areadesc.add_image(0x040000, 0x020000, FlashId::Image1, dev_id);
-            areadesc.add_image(0x060000, 0x001000, FlashId::ImageScratch, dev_id);
-
-            let mut flashmap = SimFlashMap::new();
-            flashmap.insert(dev_id, flash);
-            (flashmap, areadesc)
-        }
-        DeviceName::K64fBig => {
-            // Simulating an STM style flash on top of an NXP style flash.  Underlying flash device
-            // uses small sectors, but we tell the bootloader they are large.
-            let flash = SimFlash::new(vec![4096; 128], align as usize, erased_val);
-
-            let dev_id = 0;
-            let mut areadesc = AreaDesc::new();
-            areadesc.add_flash_sectors(dev_id, &flash);
-            areadesc.add_simple_image(0x020000, 0x020000, FlashId::Image0, dev_id);
-            areadesc.add_simple_image(0x040000, 0x020000, FlashId::Image1, dev_id);
-            areadesc.add_simple_image(0x060000, 0x020000, FlashId::ImageScratch, dev_id);
-
-            let mut flashmap = SimFlashMap::new();
-            flashmap.insert(dev_id, flash);
-            (flashmap, areadesc)
-        }
-        DeviceName::Nrf52840 => {
-            // Simulating the flash on the nrf52840 with partitions set up so that the scratch size
-            // does not divide into the image size.
-            let flash = SimFlash::new(vec![4096; 128], align as usize, erased_val);
-
-            let dev_id = 0;
-            let mut areadesc = AreaDesc::new();
-            areadesc.add_flash_sectors(dev_id, &flash);
-            areadesc.add_image(0x008000, 0x034000, FlashId::Image0, dev_id);
-            areadesc.add_image(0x03c000, 0x034000, FlashId::Image1, dev_id);
-            areadesc.add_image(0x070000, 0x00d000, FlashId::ImageScratch, dev_id);
-
-            let mut flashmap = SimFlashMap::new();
-            flashmap.insert(dev_id, flash);
-            (flashmap, areadesc)
-        }
-        DeviceName::Nrf52840SpiFlash => {
-            // Simulate nrf52840 with external SPI flash. The external SPI flash
-            // has a larger sector size so for now store scratch on that flash.
-            let flash0 = SimFlash::new(vec![4096; 128], align as usize, erased_val);
-            let flash1 = SimFlash::new(vec![8192; 64], align as usize, erased_val);
-
-            let mut areadesc = AreaDesc::new();
-            areadesc.add_flash_sectors(0, &flash0);
-            areadesc.add_flash_sectors(1, &flash1);
-
-            areadesc.add_image(0x008000, 0x068000, FlashId::Image0, 0);
-            areadesc.add_image(0x000000, 0x068000, FlashId::Image1, 1);
-            areadesc.add_image(0x068000, 0x018000, FlashId::ImageScratch, 1);
-
-            let mut flashmap = SimFlashMap::new();
-            flashmap.insert(0, flash0);
-            flashmap.insert(1, flash1);
-            (flashmap, areadesc)
-        }
-    }
-}
diff --git a/sim/tests/core.rs b/sim/tests/core.rs
index 4a6cde3..54956f0 100644
--- a/sim/tests/core.rs
+++ b/sim/tests/core.rs
@@ -2,7 +2,7 @@
 //!
 //! Run the existing testsuite as a Rust unit test.
 
-use bootsim::{Run, testlog};
+use bootsim::{ImagesBuilder, testlog};
 
 macro_rules! sim_test {
     ($name:ident, $maker:ident, $test:ident) => {
@@ -10,7 +10,7 @@
         fn $name() {
             testlog::setup();
 
-            Run::each_device(|r| {
+            ImagesBuilder::each_device(|r| {
                 let image = r.$maker();
                 assert!(!image.$test());
             });