diff --git a/CHANGELOG.md b/CHANGELOG.md
index fdfd1083..1f44cc59 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ## [Unreleased]
 ### Added
 - Add `__AVR__` to defines when compiling
+- Add support for `diditalPinToPort()`, `digitalPinToBitMask()`, and `portOutputRegister()`
 
 ### Changed
 - Move repository from https://github.com/ianfixes/arduino_ci to https://github.com/Arduino-CI/arduino_ci
diff --git a/SampleProjects/TestSomething/test/outputRegister.cpp b/SampleProjects/TestSomething/test/outputRegister.cpp
new file mode 100644
index 00000000..fa12255f
--- /dev/null
+++ b/SampleProjects/TestSomething/test/outputRegister.cpp
@@ -0,0 +1,26 @@
+#include <ArduinoUnitTests.h>
+#include <Arduino.h>
+
+// added to fix https://github.com/Arduino-CI/arduino_ci/issues/193
+// https://github.com/arduino-libraries/Ethernet/blob/master/src/utility/w5100.h#L337
+
+#if defined(__AVR__)
+unittest(portOutputRegister)
+{
+  uint8_t ss_pin = 12;
+  uint8_t ss_port = digitalPinToPort(ss_pin);
+  assertEqual(12, ss_port);
+  uint8_t *ss_pin_reg = portOutputRegister(ss_port);
+  assertEqual(GODMODE()->pMmapPort(ss_port), ss_pin_reg);
+  uint8_t ss_pin_mask = digitalPinToBitMask(ss_pin);
+  assertEqual(1, ss_pin_mask);
+
+  assertEqual((int) 1, (int) *ss_pin_reg);    // verify initial value
+  *(ss_pin_reg) &= ~ss_pin_mask;              // set SS
+  assertEqual((int) 0, (int) *ss_pin_reg);    // verify value
+  *(ss_pin_reg) |= ss_pin_mask;               // clear SS
+  assertEqual((int) 1, (int) *ss_pin_reg);    // verify value
+}
+#endif
+
+unittest_main()
diff --git a/cpp/arduino/Godmode.h b/cpp/arduino/Godmode.h
index 12fa1b51..de7a299e 100644
--- a/cpp/arduino/Godmode.h
+++ b/cpp/arduino/Godmode.h
@@ -43,6 +43,8 @@ class GodmodeState {
       uint8_t mode;
     };
 
+    uint8_t mmapPorts[MOCK_PINS_COUNT];
+
     static GodmodeState* instance;
 
   public:
@@ -87,12 +89,19 @@ class GodmodeState {
       spi.readDelayMicros = 0;
     }
 
+    void resetMmapPorts() {
+      for (int i = 0; i < MOCK_PINS_COUNT; ++i) {
+        mmapPorts[i] = 1;
+      }
+    }
+
     void reset() {
       resetClock();
       resetPins();
       resetInterrupts();
       resetPorts();
       resetSPI();
+      resetMmapPorts();
       seed = 1;
     }
 
@@ -112,6 +121,9 @@ class GodmodeState {
       return instance->micros;
     }
 
+    uint8_t* pMmapPort(uint8_t port) { return &mmapPorts[port]; }
+    uint8_t mmapPortValue(uint8_t port) { return mmapPorts[port]; }
+
     // C++ 11, declare as public for better compiler error messages
     GodmodeState(GodmodeState const&) = delete;
     void operator=(GodmodeState const&) = delete;
@@ -139,5 +151,16 @@ void detachInterrupt(uint8_t interrupt);
 inline void tone(uint8_t _pin, unsigned int frequency, unsigned long duration = 0) {}
 inline void noTone(uint8_t _pin) {}
 
+// These definitions allow the following to compile (see issue #193):
+// https://github.com/arduino-libraries/Ethernet/blob/master/src/utility/w5100.h:341
+// we allow one byte per port which "wastes" 224 bytes, but makes the code easier
+#if defined(__AVR__)
+  #define digitalPinToBitMask(pin)  (1)
+  #define digitalPinToPort(pin)     (pin)
+  #define portOutputRegister(port)  (GODMODE()->pMmapPort(port))
+#else
+  // we don't (yet) support other boards
+#endif
+
 
 GodmodeState* GODMODE();