diff --git a/fpga/include/villas/fpga/ips/i2c.hpp b/fpga/include/villas/fpga/ips/i2c.hpp
index b257ad91d..0736c7d0e 100644
--- a/fpga/include/villas/fpga/ips/i2c.hpp
+++ b/fpga/include/villas/fpga/ips/i2c.hpp
@@ -18,6 +18,13 @@ namespace villas {
 namespace fpga {
 namespace ip {
 
+#define I2C_SWTICH_ADDR 0x70
+#define I2C_SWITCH_CHANNEL_MAP                                                 \
+  { 0x20, 0x80, 0x02, 0x08, 0x10, 0x40, 0x01, 0x04 }
+#define I2C_IOEXT_ADDR 0x20
+#define I2C_IOEXT_REG_DIR 0x03
+#define I2C_IOEXT_REG_OUT 0x01
+#define I2C_EEPROM_ADDR 0x50
 class I2c : public Node {
 public:
   friend class I2cFactory;
@@ -25,7 +32,7 @@ public:
   I2c();
   virtual ~I2c();
   virtual bool init() override;
-  bool reset() override;
+  virtual bool reset() override;
   bool write(u8 address, std::vector<u8> &data);
   bool read(u8 address, std::vector<u8> &data, size_t max_read);
 
@@ -50,7 +57,7 @@ public:
     uint8_t channel;
     bool readOnce;
   };
-  Switch &getSwitch(uint8_t address = 0x70) {
+  Switch &getSwitch(uint8_t address = I2C_SWTICH_ADDR) {
     if (switchInstance == nullptr) {
       switchInstance = std::make_unique<Switch>(this, address);
     } else {
diff --git a/fpga/lib/ips/i2c.cpp b/fpga/lib/ips/i2c.cpp
index b868ce471..fd69c08e5 100644
--- a/fpga/lib/ips/i2c.cpp
+++ b/fpga/lib/ips/i2c.cpp
@@ -154,11 +154,6 @@ bool I2c::read(u8 address, std::vector<u8> &data, size_t max_read) {
 
   int retries = 10;
   while (receiveIntrs == 0 && retries > 0) {
-    ret = XIic_Start(&xIic);
-    if (ret != XST_SUCCESS) {
-      throw RuntimeError("Failed to start I2C");
-    }
-
     int intrRetries = 1;
     do {
       ret = XIic_MasterRecv(&xIic, dataPtr, max_read);
@@ -189,10 +184,9 @@ bool I2c::read(u8 address, std::vector<u8> &data, size_t max_read) {
   return XST_SUCCESS;
 }
 
-static const uint8_t CHANNEL_MAP[] = {0x20, 0x80, 0x02, 0x08,
-                                      0x10, 0x40, 0x01, 0x04};
+static const uint8_t CHANNEL_MAP[] = I2C_SWITCH_CHANNEL_MAP;
 void I2c::Switch::setChannel(uint8_t channel) {
-  if (channel > sizeof(CHANNEL_MAP) / sizeof(CHANNEL_MAP[0])) {
+  if (channel >= sizeof(CHANNEL_MAP) / sizeof(CHANNEL_MAP[0])) {
     throw RuntimeError("Invalid channel number {}", channel);
   }
   this->channel = channel;