diff --git a/src/screen.cpp b/src/io_device.cpp
similarity index 79%
rename from src/screen.cpp
rename to src/io_device.cpp
index aea1634..34df0dd 100644
--- a/src/screen.cpp
+++ b/src/io_device.cpp
@@ -1,4 +1,4 @@
-#include "screen.hpp"
+#include "io_device.hpp"
 #include <SDL2/SDL.h>
 #include <SDL2/SDL_error.h>
 #include <SDL2/SDL_render.h>
@@ -7,6 +7,7 @@
 #include <array>
 #include <cstdint>
 #include <mutex>
+#include <print>
 
 using namespace vc5;
 
@@ -62,11 +63,12 @@ constexpr auto charset = std::array {
 
 }
 
-auto Screen::create(int ch_size, int ch_width, int ch_height)
-    -> std::expected<std::unique_ptr<Screen>, std::string>
+auto IoDevice::create(int ch_size, int ch_width, int ch_height)
+    -> std::expected<std::unique_ptr<IoDevice>, std::string>
 {
     auto profile = ScreenProfile(ch_size, ch_width, ch_height);
-    auto [_0, _1, _2, px_width, px_height] = profile;
+    auto px_width= profile.px_width;
+    auto px_height = profile.px_height;
 
     if (!sdl_is_initialized) {
         if (SDL_Init(SDL_INIT_VIDEO) != 0) {
@@ -94,10 +96,10 @@ auto Screen::create(int ch_size, int ch_width, int ch_height)
 
     SDL_RenderPresent(renderer);
 
-    return std::make_unique<Screen>(profile, window, renderer, texture);
+    return std::make_unique<IoDevice>(profile, window, renderer, texture);
 }
 
-Screen::~Screen()
+IoDevice::~IoDevice()
 {
     auto lock = std::lock_guard(mx);
 
@@ -110,7 +112,7 @@ Screen::~Screen()
     }
 }
 
-auto Screen::set_char(uint16_t offset, uint8_t value)
+auto IoDevice::set_char(uint16_t offset, uint8_t value)
     -> std::expected<void, std::string>
 {
     auto lock = std::lock_guard(mx);
@@ -118,7 +120,7 @@ auto Screen::set_char(uint16_t offset, uint8_t value)
     auto it = std::find_if(charset.begin(), charset.end(), [&](Char ch) {
         return ch.ch == value;
     });
-    Char my_char = *it;
+    uint64_t char_data = it->to_u64();
 
     SDL_Color* buffer;
     int pitch;
@@ -128,19 +130,20 @@ auto Screen::set_char(uint16_t offset, uint8_t value)
     }
 
     auto [ch_size, ch_width, ch_height, px_width, px_height] = m_profile;
+    std::println("ch_size = {}, ch_width = {}, ch_height = {}, px_width = {}, px_height = {}", ch_size, ch_width, ch_height, px_width, px_height);
 
-    for (int ch_y = 0; ch_y < ch_height; ++ch_y) {
-        for (int ch_x = 0; ch_x < ch_width; ++ch_x) {
+    for (int ch_y = 0; ch_y < 8; ++ch_y) {
+        for (int ch_x = 0; ch_x < 8; ++ch_x) {
             bool ch
-                = my_char.to_u64() >> (ch_y * ch_width + (ch_width - ch_x - 1))
+                = char_data >> (ch_y * 8 + (8 - ch_x - 1))
                 & 1;
 
             for (int px_y = 0; px_y < ch_size; ++px_y) {
                 for (int px_x = 0; px_x < ch_size; ++px_x) {
 
-                    int x = (offset % ch_width * ch_size + ch_x) * px_width
+                    int x = (offset % 4 * ch_size + ch_x) * 4
                         + px_x;
-                    int y = (offset / ch_height * ch_size + ch_y) * px_height
+                    int y = (offset / 4 * ch_size + ch_y) * 4
                         + px_y;
 
                     buffer[y * px_width + x] = ch
diff --git a/src/screen.hpp b/src/io_device.hpp
similarity index 81%
rename from src/screen.hpp
rename to src/io_device.hpp
index a7bdf40..84bebe9 100644
--- a/src/screen.hpp
+++ b/src/io_device.hpp
@@ -17,8 +17,8 @@ struct ScreenProfile {
         : ch_size(ch_size)
         , ch_width(ch_width)
         , ch_height(ch_height)
-        , px_width(ch_size * ch_width)
-        , px_height(ch_size * ch_height)
+        , px_width(ch_size * 8 * ch_width)
+        , px_height(ch_size * 8 * ch_height)
     {
     }
 
@@ -29,12 +29,12 @@ struct ScreenProfile {
     int px_height;
 };
 
-class Screen {
+class IoDevice {
 public:
     static auto create(int ch_size, int ch_width, int ch_height)
-        -> std::expected<std::unique_ptr<Screen>, std::string>;
+        -> std::expected<std::unique_ptr<IoDevice>, std::string>;
 
-    explicit Screen(ScreenProfile profile,
+    explicit IoDevice(ScreenProfile profile,
         SDL_Window* window,
         SDL_Renderer* renderer,
         SDL_Texture* texture)
@@ -44,7 +44,7 @@ public:
         , m_texture(texture)
     {
     }
-    ~Screen();
+    ~IoDevice();
 
     auto set_char(uint16_t offset, uint8_t value)
         -> std::expected<void, std::string>;
diff --git a/src/main.cpp b/src/main.cpp
index db6b339..c08eef4 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1,18 +1,26 @@
 #include "builder.hpp"
-#include "screen.hpp"
+#include "io_device.hpp"
 #include <SDL2/SDL_main.h>
 #include <array>
 #include <cstdint>
 #include <print>
 #include <utility>
+#include <cstdlib>
+#include <thread>
+#include <chrono>
+
+
+using namespace std::chrono_literals;
 
 using namespace vc5;
 using R = Reg;
 
 int main()
 {
-    auto screen = Screen::create(4, 8 * 40, 8 * 24);
-    screen.value()->set_char(0, 'A');
+    auto device = IoDevice::create(4, 40, 24).value();
+    device->set_char(0, 'A').value();
+
+    std::this_thread::sleep_for(1s);
 
     constexpr R r0 = R::R0;
     constexpr R r1 = R::R1;
@@ -69,3 +77,9 @@ int main()
         std::println("{: 4x}\t{}", i, vm.word(i));
     }
 }
+
+extern "C" const char* __asan_default_options(void)
+{
+    return "detect_leaks=0";
+}
+