diff --git a/base b/base
index 5890cb8ac..b632bdf64 160000
--- a/base
+++ b/base
@@ -1 +1 @@
-Subproject commit 5890cb8ac32f29ad6d1e77edb530de239696dc44
+Subproject commit b632bdf642352990deac01e13799823a707e6229
diff --git a/frontend/device/emulator/device.lua b/frontend/device/emulator/device.lua
index 7001fa357..394dcca96 100644
--- a/frontend/device/emulator/device.lua
+++ b/frontend/device/emulator/device.lua
@@ -13,6 +13,13 @@ local Device = Generic:new{
 }
 
 function Device:init()
+    -- allows to set a viewport via environment variable
+    -- syntax is Lua table syntax, e.g. EMULATE_READER_VIEWPORT="{x=10,w=550,y=5,h=790}"
+    local viewport = os.getenv("EMULATE_READER_VIEWPORT")
+    if viewport then
+        self.viewport = require("ui/geometry"):new(loadstring("return " .. viewport)())
+    end
+
     if util.haveSDL2() then
         self.screen = require("ffi/framebuffer_SDL2_0"):new{device = self}
         self.input = require("device/input"):new{
diff --git a/frontend/device/generic/device.lua b/frontend/device/generic/device.lua
index cefe4e78d..913ea5142 100644
--- a/frontend/device/generic/device.lua
+++ b/frontend/device/generic/device.lua
@@ -44,6 +44,9 @@ function Device:init()
     end
     self.screen.debug = DEBUG
 
+    DEBUG("initializing for device", self.model)
+    DEBUG("framebuffer resolution:", self.screen:getSize())
+
     if not self.input then
         self.input = require("device/input"):new{device = self}
     end
@@ -52,6 +55,7 @@ function Device:init()
     end
 
     if self.viewport then
+        DEBUG("setting a viewport:", self.viewport)
         self.screen:setViewport(self.viewport)
         self.input:registerEventAdjustHook(
             self.input.adjustTouchTranslate,
diff --git a/frontend/device/kobo/device.lua b/frontend/device/kobo/device.lua
index 452b2c9c1..e760b7b37 100644
--- a/frontend/device/kobo/device.lua
+++ b/frontend/device/kobo/device.lua
@@ -17,16 +17,19 @@ local Kobo = Generic:new{
 
 -- TODO: hasKeys for some devices?
 
+-- Kobo Touch:
 local KoboTrilogy = Kobo:new{
     model = "Kobo_trilogy",
     touch_switch_xy = false,
 }
 
+-- Kobo Mini:
 local KoboPixie = Kobo:new{
     model = "Kobo_pixie",
     display_dpi = 200,
 }
 
+-- Kobo Aura H2O:
 local KoboDahlia = Kobo:new{
     model = "Kobo_dahlia",
     hasFrontlight = yes,
@@ -36,18 +39,21 @@ local KoboDahlia = Kobo:new{
     viewport = Geom:new{x=0, y=10, w=1080, h=1430},
 }
 
+-- Kobo Aura HD:
 local KoboDragon = Kobo:new{
     model = "Kobo_dragon",
     hasFrontlight = yes,
     display_dpi = 265,
 }
 
+-- Kobo Glo:
 local KoboKraken = Kobo:new{
     model = "Kobo_kraken",
     hasFrontlight = yes,
     display_dpi = 212,
 }
 
+-- Kobo Aura:
 local KoboPhoenix = Kobo:new{
     model = "Kobo_phoenix",
     hasFrontlight = yes,