diff --git a/.luacheckrc b/.luacheckrc
index 6738b088d..0b66404cf 100644
--- a/.luacheckrc
+++ b/.luacheckrc
@@ -4,10 +4,6 @@ std = "luajit"
 -- ignore implicit self
 self = false
 
-globals = {
-    "G_reader_settings",
-}
-
 read_globals = {
     "DLANDSCAPE_CLOCKWISE_ROTATION",
     "lfs",
diff --git a/ffi/framebuffer.lua b/ffi/framebuffer.lua
index 0206e9ed6..a8c7614bd 100644
--- a/ffi/framebuffer.lua
+++ b/ffi/framebuffer.lua
@@ -254,12 +254,12 @@ function fb:getScreenHeight()
     return self.screen_size.h
 end
 
-local screen_dpi_override
-
 function fb:getDPI()
-    if self.dpi ~= nil then return self.dpi end
+    if self.dpi ~= nil then
+        return self.dpi
+    end
 
-    self.dpi = EMULATE_READER_DPI or screen_dpi_override
+    self.dpi = EMULATE_READER_DPI
 
     if self.dpi == nil and self.device then
         self.dpi = self.device.display_dpi
@@ -273,7 +273,6 @@ function fb:getDPI()
 end
 
 function fb:setDPI(dpi)
-    screen_dpi_override = dpi
     self.dpi = dpi
 end
 
diff --git a/ffi/framebuffer_dummy.lua b/ffi/framebuffer_dummy.lua
new file mode 100644
index 000000000..0d2ae142e
--- /dev/null
+++ b/ffi/framebuffer_dummy.lua
@@ -0,0 +1,63 @@
+local BB = require("ffi/blitbuffer")
+
+local framebuffer = {}
+
+function framebuffer:init()
+    self.bb = BB.new(600, 800)
+    self.bb:fill(BB.COLOR_WHITE)
+
+    framebuffer.parent.init(self)
+end
+
+function framebuffer:resize(w, h)
+end
+
+function framebuffer:_newBB(w, h)
+    local rotation
+    local inverse
+
+    if self.bb then
+        rotation = self.bb:getRotation()
+        inverse = self.bb:getInverse() == 1
+        self.bb:free()
+    end
+    if self.invert_bb then self.invert_bb:free() end
+
+    -- we present this buffer to the outside
+    local bb = BB.new(w, h, BB.TYPE_BBRGB32)
+    local flash = os.getenv("EMULATE_READER_FLASH")
+    if flash then
+        -- in refresh emulation mode, we use a shadow blitbuffer
+        -- and blit refresh areas from it.
+        self.bb = BB.new(w, h, BB.TYPE_BBRGB32)
+    else
+        self.bb = bb
+    end
+    self.invert_bb = BB.new(w, h, BB.TYPE_BBRGB32)
+
+    if rotation then
+        self.bb:setRotation(rotation)
+    end
+
+    -- reinit inverse mode on resize
+    if inverse then
+        self.bb:invert()
+    end
+end
+
+function framebuffer:_render(bb, x, y, w, h)
+end
+
+function framebuffer:refreshFullImp(x, y, w, h)
+end
+
+function framebuffer:setWindowTitle(new_title)
+end
+
+function framebuffer:setWindowIcon(icon)
+end
+
+function framebuffer:close()
+end
+
+return require("ffi/framebuffer"):extend(framebuffer)
diff --git a/spec/unit/framebuffer_spec.lua b/spec/unit/framebuffer_spec.lua
new file mode 100644
index 000000000..5d7365f32
--- /dev/null
+++ b/spec/unit/framebuffer_spec.lua
@@ -0,0 +1,30 @@
+describe("Framebuffer unit tests", function()
+    local fb
+
+    setup(function()
+        fb = require("ffi/framebuffer_dummy"):new{
+            dummy = true,
+            device = {
+                device_dpi = 167,
+            }
+        }
+    end)
+
+    it("should set & update DPI", function()
+        assert.are.equals(160, fb:getDPI())
+
+        fb:setDPI(120)
+        assert.are.equals(120, fb:getDPI())
+
+        fb:setDPI(60)
+        assert.are.equals(60, fb:getDPI())
+    end)
+
+    it("should scale by DPI", function()
+        fb:setDPI(167)
+        assert.are.equals(30, fb:scaleBySize(30))
+
+        fb:setDPI(167 * 3)
+        assert.are.equals(60, fb:scaleBySize(30))
+    end)
+end)