diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 0fda0cc..22e6ba8 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -7,9 +7,9 @@ jobs:
       GLOBAL_CACHE_VERSION: 1
       PBDOOM_PATH: pbdoom
       SDK_DOWNLOAD_PATH: sdk
-      SDK_REPO: pocketbook/SDK_6.3.0
-      SDK_REF: 23eb32c3a011a1df4ce3d8f22150dcdd34cbc75a
-      SDK_VARIANT: SDK-A13
+      SDK_REPO: blchinezu/pocketbook-sdk
+      SDK_REF: 64e9fa210dd90569f8eabea92da4d40f3d072fc1
+      SDK_VARIANT: SDK_481
     steps:
       - name: Checkout repo
         uses: actions/checkout@v3
@@ -46,7 +46,7 @@ jobs:
 
       - name: Build
         run: |
-          $SDK_DOWNLOAD_PATH/$SDK_VARIANT/bin/update_path.sh
+          sed -i "s@/srv/einkbuild/SDK2FREE/SDK-481@$(pwd)/$SDK_DOWNLOAD_PATH/$SDK_VARIANT@g" $SDK_DOWNLOAD_PATH/$SDK_VARIANT/share/cmake/arm_conf.cmake
 
           cd $PBDOOM_PATH
           echo "../$SDK_DOWNLOAD_PATH/$SDK_VARIANT" > sdk_path
diff --git a/.gitignore b/.gitignore
index c795b05..7abc51c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
-build
\ No newline at end of file
+build
+*.~undo-tree~
\ No newline at end of file
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1b97805..924a70c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- Removed `DitherAreaPattern2Level` dithering mode because it is not supported in the older SDK
+- Support for older devices (min GLIBC 2.4) like PocketBook 611 [#9](https://github.com/imustafin/pbdoom/issues/9)
+
 ### Fixed
 
 ## [v0.0.5]
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 20468fb..4832932 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -24,7 +24,6 @@ configure_file(
 include_directories(${CMAKE_BINARY_DIR}/generated)
 ### end version
 
-
 add_executable(game.app
   main.c
   pbdoom_state.h
@@ -173,5 +172,7 @@ sdldoom-1.10/z_zone.h
 )
 target_link_libraries(game.app ${INKVIEW_LIBRARIES})
 target_link_libraries(game.app m)
+target_link_libraries(game.app rt)
 
-target_compile_options(game.app PRIVATE -Werror=implicit-function-declaration)
+target_compile_options(game.app PRIVATE -Werror=implicit-function-declaration -D_GNU_SOURCE -fsigned-char)
+set_property(TARGET game.app PROPERTY C_STANDARD 99)
diff --git a/build.sh b/build.sh
index 5522509..3fcce9e 100755
--- a/build.sh
+++ b/build.sh
@@ -1,2 +1,3 @@
+export LC_ALL=C
 SDK_PATH=$(cat sdk_path)
 mkdir -p build && cd build && cmake -DCMAKE_TOOLCHAIN_FILE=$SDK_PATH/share/cmake/arm_conf.cmake .. && cmake --build .
diff --git a/pages/_data/i18n.yml b/pages/_data/i18n.yml
index f0bfab2..6782881 100644
--- a/pages/_data/i18n.yml
+++ b/pages/_data/i18n.yml
@@ -25,6 +25,10 @@ home:
     en: 'PBDoom is known to be running on:'
     ru: 'Известно, что PBDoom работает на этих устройствах:'
     tt: 'PBDoom бу җайланмаларда эшләве билгеле:'
+  device_compat_limited_desc:
+    en: 'PBDoom starts but works with limited functionality on:'
+    ru: 'PBDoom запускается, но работает в ограниченном режиме на:'
+    tt: 'PBDoom бу җайланмаларда башлый ала, ләкин чикләнгән функционалда эшли:'
   source_code_and_contacts:
     en: Source code and contacts
     ru: Исходный код и контакты
diff --git a/pages/_layouts/home.html b/pages/_layouts/home.html
index 9f86870..919bb3c 100644
--- a/pages/_layouts/home.html
+++ b/pages/_layouts/home.html
@@ -87,6 +87,10 @@ <h2 class="text-2xl font-bold mt-2 mb-1">
         <li>PocketBook X</li>
         <li>PocketBook Touch HD 3</li>
       </ul>
+      {{ site.data.i18n.home.device_compat_limited_desc | t }}
+      <ul class="list-disc list-inside">
+        <li>PocketBook 611</li>
+      </ul>
       <h2 class="text-2xl font-bold mt-2 mb-1">
         {{ site.data.i18n.home.source_code_and_contacts | t }}
       </h2>
diff --git a/pbdoom-get.app b/pbdoom-get.app
index 472e6a3..d5be7f5 100644
--- a/pbdoom-get.app
+++ b/pbdoom-get.app
@@ -20,7 +20,7 @@ do
     nc -l -p "$LOCAL_PORT" > "$LOCAL_APP_PATH"
     echo "Application has been saved to '$LOCAL_APP_PATH'"
 
-    MON_IP=192.168.43.248
+    MON_IP=192.168.3.224
     MON_PORT=10002
     pbdoom.app | nc $MON_IP $MON_PORT
 done
diff --git a/pbdoom/frames/color_settings.c b/pbdoom/frames/color_settings.c
index 8ead744..49a9ddc 100644
--- a/pbdoom/frames/color_settings.c
+++ b/pbdoom/frames/color_settings.c
@@ -211,7 +211,7 @@ static void uninstall() {
   
 }
 
-const int NUM_BUF_S = 10;
+#define NUM_BUF_S 10
 char num_buf[NUM_BUF_S];
 
 void draw_value_text(value *v) {
diff --git a/pbdoom/frames/game.c b/pbdoom/frames/game.c
index c55edf9..5ab34d8 100644
--- a/pbdoom/frames/game.c
+++ b/pbdoom/frames/game.c
@@ -119,10 +119,6 @@ void game_frame_draw_screen(unsigned char *screen) {
   case DYNAMIC_A2:
     DynamicUpdateA2(ux, uy, uw, uh);
     break;
-  case DITHER_AREA_PATTERN_2_LEVEL:
-    DitherAreaPattern2Level(ux, uy, uw, uh);
-    PartialUpdate(ux, uy, uw, uh);
-    break;
   case DITHER_MANUAL_2_PATTERN:
     DitherArea(ux, uy, uw, uh, 2, DITHER_PATTERN);
     PartialUpdate(ux, uy, uw, uh);
diff --git a/pbdoom/frames/game.h b/pbdoom/frames/game.h
index 7848fc4..50b7961 100644
--- a/pbdoom/frames/game.h
+++ b/pbdoom/frames/game.h
@@ -9,7 +9,6 @@ extern frame game_frame;
 
 typedef enum {
   DYNAMIC_A2,
-  DITHER_AREA_PATTERN_2_LEVEL,
   DITHER_MANUAL_2_PATTERN,
   NO_DITHER
 } ink_render_mode;
@@ -19,9 +18,9 @@ void game_frame_set_render_mode(ink_render_mode i_render_mode);
 void game_frame_set_palette(byte *palette);
 void game_frame_draw_screen(unsigned char *screen);
 
-static const double GAME_DEFAULT_ALPHA = 1;
-static const double GAME_DEFAULT_BETA = 0;
-static const double GAME_DEFAULT_GAMMA = 1;
+#define GAME_DEFAULT_ALPHA 1
+#define GAME_DEFAULT_BETA 0
+#define GAME_DEFAULT_GAMMA 1
 extern double game_alpha;
 extern double game_beta;
 extern double game_gamma;
diff --git a/pbdoom/frames/panel.c b/pbdoom/frames/panel.c
index b3b8496..0b522ae 100644
--- a/pbdoom/frames/panel.c
+++ b/pbdoom/frames/panel.c
@@ -9,7 +9,6 @@ icontext_menu *main_menu;
 enum {
   idx_render = 1,
   idx_render_dynamic_a2,
-  idx_render_dither_area_pattern_2_level,
   idx_render_dither_area_2,
   idx_render_no_dither,
 
@@ -24,11 +23,6 @@ imenu render_submenu[] = {
     idx_render_dynamic_a2,
     "DynamicA2"
   },
-  {
-    ITEM_ACTIVE,
-    idx_render_dither_area_pattern_2_level,
-    "DitherAreaPattern2Level"
-  },
   {
     ITEM_ACTIVE,
     idx_render_dither_area_2,
@@ -97,10 +91,6 @@ void main_menu_handler(int i) {
     send_render_event(DYNAMIC_A2);
     main_menu = NULL;
     break;
-  case idx_render_dither_area_pattern_2_level:
-    send_render_event(DITHER_AREA_PATTERN_2_LEVEL);
-    main_menu = NULL;
-    break;
   case idx_render_dither_area_2:
     send_render_event(DITHER_MANUAL_2_PATTERN);
     main_menu = NULL;
@@ -126,9 +116,6 @@ void make_main_menu() {
   case DYNAMIC_A2:
     active_idx = idx_render_dynamic_a2;
     break;
-  case DITHER_AREA_PATTERN_2_LEVEL:
-    active_idx = idx_render_dither_area_pattern_2_level;
-    break;
   case DITHER_MANUAL_2_PATTERN:
     active_idx = idx_render_dither_area_2;
     break;
diff --git a/send.sh b/send.sh
index 20282ea..010b717 100755
--- a/send.sh
+++ b/send.sh
@@ -4,7 +4,7 @@ set -e
 
 LOCAL_PATH=./build/game.app
 REMOTE_APP_NAME=pbdoom/game.app
-REMOTE_IP=192.168.43.40
+REMOTE_IP=192.168.3.211
 REMOTE_PORT=10003
 
 echo "Sending '$LOCAL_PATH' to '$REMOTE_IP:$REMOTE_PORT/$REMOTE_APP_NAME'"