diff --git a/serial_link/protocol/byte_stuffer.c b/serial_link/protocol/byte_stuffer.c
index e5a26c2c..05b7aa6f 100644
--- a/serial_link/protocol/byte_stuffer.c
+++ b/serial_link/protocol/byte_stuffer.c
@@ -32,6 +32,7 @@ SOFTWARE.
 // http://www.stuartcheshire.org/papers/COBSforToN.pdf
 
 #define MAX_FRAME_SIZE 1024
+#define NUM_LINKS 2
 
 typedef struct byte_stuffer_state {
     uint16_t next_zero;
@@ -40,70 +41,78 @@ typedef struct byte_stuffer_state {
     uint8_t data[MAX_FRAME_SIZE];
 }byte_stuffer_state_t;
 
-static byte_stuffer_state_t state;
+static byte_stuffer_state_t states[NUM_LINKS];
+
+void init_byte_stuffer_state(byte_stuffer_state_t* state) {
+    state->next_zero = 0;
+    state->data_pos = 0;
+    state->long_frame = false;
+}
 
 void init_byte_stuffer(void) {
-    state.next_zero = 0;
-    state.data_pos = 0;
-    state.long_frame = false;
+    int i;
+    for (i=0;i<NUM_LINKS;i++) {
+        init_byte_stuffer_state(&states[i]);
+    }
 }
 
-void recv_byte(uint8_t data) {
+void recv_byte(uint8_t link, uint8_t data) {
+    byte_stuffer_state_t* state = &states[link];
     // Start of a new frame
-    if (state.next_zero == 0) {
-        state.next_zero = data;
-        state.long_frame = data == 0xFF;
-        state.data_pos = 0;
+    if (state->next_zero == 0) {
+        state->next_zero = data;
+        state->long_frame = data == 0xFF;
+        state->data_pos = 0;
         return;
     }
 
-    state.next_zero--;
+    state->next_zero--;
     if (data == 0) {
-        if (state.next_zero == 0) {
+        if (state->next_zero == 0) {
             // The frame is completed
-            if (state.data_pos > 0) {
-                validator_recv_frame(state.data, state.data_pos);
+            if (state->data_pos > 0) {
+                validator_recv_frame(link, state->data, state->data_pos);
             }
         }
         else {
             // The frame is invalid, so reset
-            init_byte_stuffer();
+            init_byte_stuffer_state(state);
         }
     }
     else {
-        if (state.data_pos == MAX_FRAME_SIZE) {
+        if (state->data_pos == MAX_FRAME_SIZE) {
             // We exceeded our maximum frame size
             // therefore there's nothing else to do than reset to a new frame
-            state.next_zero = data;
-            state.long_frame = data == 0xFF;
-            state.data_pos = 0;
+            state->next_zero = data;
+            state->long_frame = data == 0xFF;
+            state->data_pos = 0;
         }
-        else if (state.next_zero == 0) {
-            if (state.long_frame) {
+        else if (state->next_zero == 0) {
+            if (state->long_frame) {
                 // This is part of a long frame, so continue
-                state.next_zero = data;
-                state.long_frame = data == 0xFF;
+                state->next_zero = data;
+                state->long_frame = data == 0xFF;
             }
             else {
                 // Special case for zeroes
-                state.next_zero = data;
-                state.data[state.data_pos++] = 0;
+                state->next_zero = data;
+                state->data[state->data_pos++] = 0;
             }
         }
         else {
-            state.data[state.data_pos++] = data;
+            state->data[state->data_pos++] = data;
         }
     }
 }
 
-static void send_block(uint8_t* start, uint8_t* end, uint8_t num_non_zero) {
-    send_data(&num_non_zero, 1);
+static void send_block(uint8_t link, uint8_t* start, uint8_t* end, uint8_t num_non_zero) {
+    send_data(link, &num_non_zero, 1);
     if (end > start) {
-        send_data(start, end-start);
+        send_data(link, start, end-start);
     }
 }
 
-void send_frame(uint8_t* data, uint16_t size) {
+void send_frame(uint8_t link, uint8_t* data, uint16_t size) {
     const uint8_t zero = 0;
     if (size > 0) {
         uint16_t num_non_zero = 1;
@@ -113,14 +122,14 @@ void send_frame(uint8_t* data, uint16_t size) {
             if (num_non_zero == 0xFF) {
                 // There's more data after big non-zero block
                 // So send it, and start a new block
-                send_block(start, data, num_non_zero);
+                send_block(link, start, data, num_non_zero);
                 start = data;
                 num_non_zero = 1;
             }
             else {
                 if (*data == 0) {
                     // A zero encountered, so send the block
-                    send_block(start, data, num_non_zero);
+                    send_block(link, start, data, num_non_zero);
                     start = data + 1;
                     num_non_zero = 1;
                 }
@@ -130,7 +139,7 @@ void send_frame(uint8_t* data, uint16_t size) {
                 ++data;
             }
         }
-        send_block(start, data, num_non_zero);
-        send_data(&zero, 1);
+        send_block(link, start, data, num_non_zero);
+        send_data(link, &zero, 1);
     }
 }
diff --git a/serial_link/protocol/byte_stuffer.h b/serial_link/protocol/byte_stuffer.h
index 4dcdd24c..cd94b458 100644
--- a/serial_link/protocol/byte_stuffer.h
+++ b/serial_link/protocol/byte_stuffer.h
@@ -23,5 +23,5 @@ SOFTWARE.
 */
 
 void init_byte_stuffer(void);
-void recv_byte(uint8_t data);
-void send_frame(uint8_t* data, uint16_t size);
+void recv_byte(uint8_t link, uint8_t data);
+void send_frame(uint8_t link, uint8_t* data, uint16_t size);
diff --git a/serial_link/protocol/frame_router.h b/serial_link/protocol/frame_router.h
index dd1bfb12..3906b06c 100644
--- a/serial_link/protocol/frame_router.h
+++ b/serial_link/protocol/frame_router.h
@@ -22,4 +22,4 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 */
 
-void route_incoming_frame(uint8_t* data, uint16_t size);
+void route_incoming_frame(uint8_t link, uint8_t* data, uint16_t size);
diff --git a/serial_link/protocol/frame_validator.c b/serial_link/protocol/frame_validator.c
index f326097f..80e662b2 100644
--- a/serial_link/protocol/frame_validator.c
+++ b/serial_link/protocol/frame_validator.c
@@ -102,19 +102,19 @@ static uint32_t crc32_byte(uint8_t *p, uint32_t bytelength)
     return (crc ^ 0xffffffff);
 }
 
-void validator_recv_frame(uint8_t* data, uint16_t size) {
+void validator_recv_frame(uint8_t link, uint8_t* data, uint16_t size) {
     if (size > 4) {
         uint32_t frame_crc;
         memcpy(&frame_crc, data + size -4, 4);
         uint32_t expected_crc = crc32_byte(data, size - 4);
         if (frame_crc == expected_crc) {
-            route_incoming_frame(data, size-4);
+            route_incoming_frame(link, data, size-4);
         }
     }
 }
 
-void validator_send_frame(uint8_t* data, uint16_t size) {
+void validator_send_frame(uint8_t link, uint8_t* data, uint16_t size) {
     uint32_t crc = crc32_byte(data, size);
     memcpy(data + size, &crc, 4);
-    send_frame(data, size + 4);
+    send_frame(link, data, size + 4);
 }
diff --git a/serial_link/protocol/frame_validator.h b/serial_link/protocol/frame_validator.h
index 2e518894..c35fc272 100644
--- a/serial_link/protocol/frame_validator.h
+++ b/serial_link/protocol/frame_validator.h
@@ -22,6 +22,6 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 */
 
-void validator_recv_frame(uint8_t* data, uint16_t size);
+void validator_recv_frame(uint8_t link, uint8_t* data, uint16_t size);
 // The buffer pointed to by the data needs 4 additional bytes
-void validator_send_frame(uint8_t* data, uint16_t size);
+void validator_send_frame(uint8_t link, uint8_t* data, uint16_t size);
diff --git a/serial_link/protocol/physical.h b/serial_link/protocol/physical.h
index 73a7855d..ee5883d3 100644
--- a/serial_link/protocol/physical.h
+++ b/serial_link/protocol/physical.h
@@ -22,4 +22,4 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 */
 
-void send_data(const uint8_t* data, uint16_t size);
+void send_data(uint8_t link, const uint8_t* data, uint16_t size);
diff --git a/serial_link/tests/byte_stuffer_tests.c b/serial_link/tests/byte_stuffer_tests.c
index f29cc129..0f58479c 100644
--- a/serial_link/tests/byte_stuffer_tests.c
+++ b/serial_link/tests/byte_stuffer_tests.c
@@ -39,34 +39,34 @@ BeforeEach(ByteStuffer) {
 }
 AfterEach(ByteStuffer) {}
 
-void validator_recv_frame(uint8_t* data, uint16_t size) {
+void validator_recv_frame(uint8_t link, uint8_t* data, uint16_t size) {
     mock(data, size);
 }
 
-void send_data(const uint8_t* data, uint16_t size) {
+void send_data(uint8_t link, const uint8_t* data, uint16_t size) {
     memcpy(sent_data + sent_data_size, data, size);
     sent_data_size += size;
 }
 
 Ensure(ByteStuffer, receives_no_frame_for_a_single_zero_byte) {
     never_expect(validator_recv_frame);
-    recv_byte(0);
+    recv_byte(0, 0);
 }
 
 Ensure(ByteStuffer, receives_no_frame_for_a_single_FF_byte) {
     never_expect(validator_recv_frame);
-    recv_byte(0xFF);
+    recv_byte(0, 0xFF);
 }
 
 Ensure(ByteStuffer, receives_no_frame_for_a_single_random_byte) {
     never_expect(validator_recv_frame);
-    recv_byte(0x4A);
+    recv_byte(0, 0x4A);
 }
 
 Ensure(ByteStuffer, receives_no_frame_for_a_zero_length_frame) {
     never_expect(validator_recv_frame);
-    recv_byte(1);
-    recv_byte(0);
+    recv_byte(0, 1);
+    recv_byte(0, 0);
 }
 
 Ensure(ByteStuffer, receives_single_byte_valid_frame) {
@@ -75,9 +75,9 @@ Ensure(ByteStuffer, receives_single_byte_valid_frame) {
         when(size, is_equal_to(1)),
         when(data, is_equal_to_contents_of(expected, 1))
     );
-    recv_byte(2);
-    recv_byte(0x37);
-    recv_byte(0);
+    recv_byte(0, 2);
+    recv_byte(0, 0x37);
+    recv_byte(0, 0);
 }
 
 Ensure(ByteStuffer, receives_three_bytes_valid_frame) {
@@ -86,11 +86,11 @@ Ensure(ByteStuffer, receives_three_bytes_valid_frame) {
         when(size, is_equal_to(3)),
         when(data, is_equal_to_contents_of(expected, 3))
     );
-    recv_byte(4);
-    recv_byte(0x37);
-    recv_byte(0x99);
-    recv_byte(0xFF);
-    recv_byte(0);
+    recv_byte(0, 4);
+    recv_byte(0, 0x37);
+    recv_byte(0, 0x99);
+    recv_byte(0, 0xFF);
+    recv_byte(0, 0);
 }
 
 Ensure(ByteStuffer, receives_single_zero_valid_frame) {
@@ -99,9 +99,9 @@ Ensure(ByteStuffer, receives_single_zero_valid_frame) {
         when(size, is_equal_to(1)),
         when(data, is_equal_to_contents_of(expected, 1))
     );
-    recv_byte(1);
-    recv_byte(1);
-    recv_byte(0);
+    recv_byte(0, 1);
+    recv_byte(0, 1);
+    recv_byte(0, 0);
 }
 
 Ensure(ByteStuffer, receives_valid_frame_with_zeroes) {
@@ -110,12 +110,12 @@ Ensure(ByteStuffer, receives_valid_frame_with_zeroes) {
         when(size, is_equal_to(4)),
         when(data, is_equal_to_contents_of(expected, 4))
     );
-    recv_byte(2);
-    recv_byte(5);
-    recv_byte(2);
-    recv_byte(3);
-    recv_byte(1);
-    recv_byte(0);
+    recv_byte(0, 2);
+    recv_byte(0, 5);
+    recv_byte(0, 2);
+    recv_byte(0, 3);
+    recv_byte(0, 1);
+    recv_byte(0, 0);
 }
 
 Ensure(ByteStuffer, receives_two_valid_frames) {
@@ -129,13 +129,13 @@ Ensure(ByteStuffer, receives_two_valid_frames) {
         when(size, is_equal_to(1)),
         when(data, is_equal_to_contents_of(expected2, 1))
     );
-    recv_byte(2);
-    recv_byte(5);
-    recv_byte(1);
-    recv_byte(0);
-    recv_byte(2);
-    recv_byte(3);
-    recv_byte(0);
+    recv_byte(1, 2);
+    recv_byte(1, 5);
+    recv_byte(1, 1);
+    recv_byte(1, 0);
+    recv_byte(1, 2);
+    recv_byte(1, 3);
+    recv_byte(1, 0);
 }
 
 Ensure(ByteStuffer, receives_valid_frame_after_unexpected_zero) {
@@ -144,13 +144,13 @@ Ensure(ByteStuffer, receives_valid_frame_after_unexpected_zero) {
         when(size, is_equal_to(2)),
         when(data, is_equal_to_contents_of(expected, 2))
     );
-    recv_byte(3);
-    recv_byte(1);
-    recv_byte(0);
-    recv_byte(3);
-    recv_byte(5);
-    recv_byte(7);
-    recv_byte(0);
+    recv_byte(1, 3);
+    recv_byte(1, 1);
+    recv_byte(1, 0);
+    recv_byte(1, 3);
+    recv_byte(1, 5);
+    recv_byte(1, 7);
+    recv_byte(1, 0);
 }
 
 Ensure(ByteStuffer, receives_valid_frame_after_unexpected_non_zero) {
@@ -159,14 +159,14 @@ Ensure(ByteStuffer, receives_valid_frame_after_unexpected_non_zero) {
         when(size, is_equal_to(2)),
         when(data, is_equal_to_contents_of(expected, 2))
     );
-    recv_byte(2);
-    recv_byte(9);
-    recv_byte(4); // This should have been zero
-    recv_byte(0);
-    recv_byte(3);
-    recv_byte(5);
-    recv_byte(7);
-    recv_byte(0);
+    recv_byte(0, 2);
+    recv_byte(0, 9);
+    recv_byte(0, 4); // This should have been zero
+    recv_byte(0, 0);
+    recv_byte(0, 3);
+    recv_byte(0, 5);
+    recv_byte(0, 7);
+    recv_byte(0, 0);
 }
 
 Ensure(ByteStuffer, receives_a_valid_frame_with_over254_non_zeroes_and_then_end_of_frame) {
@@ -179,11 +179,11 @@ Ensure(ByteStuffer, receives_a_valid_frame_with_over254_non_zeroes_and_then_end_
         when(size, is_equal_to(254)),
         when(data, is_equal_to_contents_of(expected, 254))
     );
-    recv_byte(0xFF);
+    recv_byte(0, 0xFF);
     for (i=0;i<254;i++) {
-        recv_byte(i+1);
+        recv_byte(0, i+1);
     }
-    recv_byte(0);
+    recv_byte(0, 0);
 }
 
 Ensure(ByteStuffer, receives_a_valid_frame_with_over254_non_zeroes_next_byte_is_non_zero) {
@@ -197,13 +197,13 @@ Ensure(ByteStuffer, receives_a_valid_frame_with_over254_non_zeroes_next_byte_is_
         when(size, is_equal_to(255)),
         when(data, is_equal_to_contents_of(expected, 255))
     );
-    recv_byte(0xFF);
+    recv_byte(0, 0xFF);
     for (i=0;i<254;i++) {
-        recv_byte(i+1);
+        recv_byte(0, i+1);
     }
-    recv_byte(2);
-    recv_byte(7);
-    recv_byte(0);
+    recv_byte(0, 2);
+    recv_byte(0, 7);
+    recv_byte(0, 0);
 }
 
 Ensure(ByteStuffer, receives_a_valid_frame_with_over254_non_zeroes_next_byte_is_zero) {
@@ -217,13 +217,13 @@ Ensure(ByteStuffer, receives_a_valid_frame_with_over254_non_zeroes_next_byte_is_
         when(size, is_equal_to(255)),
         when(data, is_equal_to_contents_of(expected, 255))
     );
-    recv_byte(0xFF);
+    recv_byte(0, 0xFF);
     for (i=0;i<254;i++) {
-        recv_byte(i+1);
+        recv_byte(0, i+1);
     }
-    recv_byte(1);
-    recv_byte(1);
-    recv_byte(0);
+    recv_byte(0, 1);
+    recv_byte(0, 1);
+    recv_byte(0, 0);
 }
 
 Ensure(ByteStuffer, receives_two_long_frames_and_some_more) {
@@ -242,23 +242,23 @@ Ensure(ByteStuffer, receives_two_long_frames_and_some_more) {
         when(size, is_equal_to(515)),
         when(data, is_equal_to_contents_of(expected, 510))
     );
-    recv_byte(0xFF);
+    recv_byte(0, 0xFF);
     for (i=0;i<254;i++) {
-        recv_byte(i+1);
+        recv_byte(0, i+1);
     }
-    recv_byte(0xFF);
+    recv_byte(0, 0xFF);
     for (i=0;i<254;i++) {
-        recv_byte(i+1);
+        recv_byte(0, i+1);
     }
-    recv_byte(8);
-    recv_byte(1);
-    recv_byte(2);
-    recv_byte(3);
-    recv_byte(4);
-    recv_byte(5);
-    recv_byte(6);
-    recv_byte(7);
-    recv_byte(0);
+    recv_byte(0, 8);
+    recv_byte(0, 1);
+    recv_byte(0, 2);
+    recv_byte(0, 3);
+    recv_byte(0, 4);
+    recv_byte(0, 5);
+    recv_byte(0, 6);
+    recv_byte(0, 7);
+    recv_byte(0, 0);
 }
 
 Ensure(ByteStuffer, receives_an_all_zeros_frame_that_is_maximum_size) {
@@ -268,23 +268,23 @@ Ensure(ByteStuffer, receives_an_all_zeros_frame_that_is_maximum_size) {
         when(data, is_equal_to_contents_of(expected, MAX_FRAME_SIZE))
     );
     int i;
-    recv_byte(1);
+    recv_byte(0, 1);
     for(i=0;i<MAX_FRAME_SIZE;i++) {
-       recv_byte(1);
+       recv_byte(0, 1);
     }
-    recv_byte(0);
+    recv_byte(0, 0);
 }
 
 Ensure(ByteStuffer, doesnt_recv_a_frame_thats_too_long_all_zeroes) {
     uint8_t expected[1] = {0};
     never_expect(validator_recv_frame);
     int i;
-    recv_byte(1);
+    recv_byte(0, 1);
     for(i=0;i<MAX_FRAME_SIZE;i++) {
-       recv_byte(1);
+       recv_byte(0, 1);
     }
-    recv_byte(1);
-    recv_byte(0);
+    recv_byte(0, 1);
+    recv_byte(0, 0);
 }
 
 Ensure(ByteStuffer, received_frame_is_aborted_when_its_too_long) {
@@ -294,23 +294,23 @@ Ensure(ByteStuffer, received_frame_is_aborted_when_its_too_long) {
         when(data, is_equal_to_contents_of(expected, 1))
     );
     int i;
-    recv_byte(1);
+    recv_byte(0, 1);
     for(i=0;i<MAX_FRAME_SIZE;i++) {
-       recv_byte(1);
+       recv_byte(0, 1);
     }
-    recv_byte(2);
-    recv_byte(1);
-    recv_byte(0);
+    recv_byte(0, 2);
+    recv_byte(0, 1);
+    recv_byte(0, 0);
 }
 
 Ensure(ByteStuffer, does_nothing_when_sending_zero_size_frame) {
     assert_that(sent_data_size, is_equal_to(0));
-    send_frame(NULL, 0);
+    send_frame(0, NULL, 0);
 }
 
 Ensure(ByteStuffer, send_one_byte_frame) {
     uint8_t data[] = {5};
-    send_frame(data, 1);
+    send_frame(1, data, 1);
     uint8_t expected[] = {2, 5, 0};
     assert_that(sent_data_size, is_equal_to(sizeof(expected)));
     assert_that(sent_data, is_equal_to_contents_of(expected, sizeof(expected)));
@@ -318,7 +318,7 @@ Ensure(ByteStuffer, send_one_byte_frame) {
 
 Ensure(ByteStuffer, sends_two_byte_frame) {
     uint8_t data[] = {5, 0x77};
-    send_frame(data, 2);
+    send_frame(0, data, 2);
     uint8_t expected[] = {3, 5, 0x77, 0};
     assert_that(sent_data_size, is_equal_to(sizeof(expected)));
     assert_that(sent_data, is_equal_to_contents_of(expected, sizeof(expected)));
@@ -326,7 +326,7 @@ Ensure(ByteStuffer, sends_two_byte_frame) {
 
 Ensure(ByteStuffer, sends_one_byte_frame_with_zero) {
     uint8_t data[] = {0};
-    send_frame(data, 1);
+    send_frame(0, data, 1);
     uint8_t expected[] = {1, 1, 0};
     assert_that(sent_data_size, is_equal_to(sizeof(expected)));
     assert_that(sent_data, is_equal_to_contents_of(expected, sizeof(expected)));
@@ -334,7 +334,7 @@ Ensure(ByteStuffer, sends_one_byte_frame_with_zero) {
 
 Ensure(ByteStuffer, sends_two_byte_frame_starting_with_zero) {
     uint8_t data[] = {0, 9};
-    send_frame(data, 2);
+    send_frame(1, data, 2);
     uint8_t expected[] = {1, 2, 9, 0};
     assert_that(sent_data_size, is_equal_to(sizeof(expected)));
     assert_that(sent_data, is_equal_to_contents_of(expected, sizeof(expected)));
@@ -342,7 +342,7 @@ Ensure(ByteStuffer, sends_two_byte_frame_starting_with_zero) {
 
 Ensure(ByteStuffer, sends_two_byte_frame_starting_with_non_zero) {
     uint8_t data[] = {9, 0};
-    send_frame(data, 2);
+    send_frame(1, data, 2);
     uint8_t expected[] = {2, 9, 1, 0};
     assert_that(sent_data_size, is_equal_to(sizeof(expected)));
     assert_that(sent_data, is_equal_to_contents_of(expected, sizeof(expected)));
@@ -350,7 +350,7 @@ Ensure(ByteStuffer, sends_two_byte_frame_starting_with_non_zero) {
 
 Ensure(ByteStuffer, sends_three_byte_frame_zero_in_the_middle) {
     uint8_t data[] = {9, 0, 0x68};
-    send_frame(data, 3);
+    send_frame(0, data, 3);
     uint8_t expected[] = {2, 9, 2, 0x68, 0};
     assert_that(sent_data_size, is_equal_to(sizeof(expected)));
     assert_that(sent_data, is_equal_to_contents_of(expected, sizeof(expected)));
@@ -358,7 +358,7 @@ Ensure(ByteStuffer, sends_three_byte_frame_zero_in_the_middle) {
 
 Ensure(ByteStuffer, sends_three_byte_frame_data_in_the_middle) {
     uint8_t data[] = {0, 0x55, 0};
-    send_frame(data, 3);
+    send_frame(0, data, 3);
     uint8_t expected[] = {1, 2, 0x55, 1, 0};
     assert_that(sent_data_size, is_equal_to(sizeof(expected)));
     assert_that(sent_data, is_equal_to_contents_of(expected, sizeof(expected)));
@@ -366,7 +366,7 @@ Ensure(ByteStuffer, sends_three_byte_frame_data_in_the_middle) {
 
 Ensure(ByteStuffer, sends_three_byte_frame_with_all_zeroes) {
     uint8_t data[] = {0, 0, 0};
-    send_frame(data, 3);
+    send_frame(0, data, 3);
     uint8_t expected[] = {1, 1, 1, 1, 0};
     assert_that(sent_data_size, is_equal_to(sizeof(expected)));
     assert_that(sent_data, is_equal_to_contents_of(expected, sizeof(expected)));
@@ -378,7 +378,7 @@ Ensure(ByteStuffer, sends_frame_with_254_non_zeroes) {
     for(i=0;i<254;i++) {
         data[i] = i + 1;
     }
-    send_frame(data, 254);
+    send_frame(0, data, 254);
     uint8_t expected[256];
     expected[0] = 0xFF;
     for(i=1;i<255;i++) {
@@ -395,7 +395,7 @@ Ensure(ByteStuffer, sends_frame_with_255_non_zeroes) {
     for(i=0;i<255;i++) {
         data[i] = i + 1;
     }
-    send_frame(data, 255);
+    send_frame(0, data, 255);
     uint8_t expected[258];
     expected[0] = 0xFF;
     for(i=1;i<255;i++) {
@@ -415,7 +415,7 @@ Ensure(ByteStuffer, sends_frame_with_254_non_zeroes_followed_by_zero) {
         data[i] = i + 1;
     }
     data[255] = 0;
-    send_frame(data, 255);
+    send_frame(0, data, 255);
     uint8_t expected[258];
     expected[0] = 0xFF;
     for(i=1;i<255;i++) {
@@ -430,27 +430,27 @@ Ensure(ByteStuffer, sends_frame_with_254_non_zeroes_followed_by_zero) {
 
 Ensure(ByteStuffer, sends_and_receives_full_roundtrip_small_packet) {
     uint8_t original_data[] = { 1, 2, 3};
-    send_frame(original_data, sizeof(original_data));
+    send_frame(0, original_data, sizeof(original_data));
     expect(validator_recv_frame,
         when(size, is_equal_to(sizeof(original_data))),
         when(data, is_equal_to_contents_of(original_data, sizeof(original_data)))
     );
     int i;
     for(i=0;i<sent_data_size;i++) {
-       recv_byte(sent_data[i]);
+       recv_byte(1, sent_data[i]);
     }
 }
 
 Ensure(ByteStuffer, sends_and_receives_full_roundtrip_small_packet_with_zeros) {
     uint8_t original_data[] = { 1, 0, 3, 0, 0, 9};
-    send_frame(original_data, sizeof(original_data));
+    send_frame(1, original_data, sizeof(original_data));
     expect(validator_recv_frame,
         when(size, is_equal_to(sizeof(original_data))),
         when(data, is_equal_to_contents_of(original_data, sizeof(original_data)))
     );
     int i;
     for(i=0;i<sent_data_size;i++) {
-       recv_byte(sent_data[i]);
+       recv_byte(0, sent_data[i]);
     }
 }
 
@@ -460,13 +460,13 @@ Ensure(ByteStuffer, sends_and_receives_full_roundtrip_254_bytes) {
     for(i=0;i<254;i++) {
         original_data[i] = i + 1;
     }
-    send_frame(original_data, sizeof(original_data));
+    send_frame(0, original_data, sizeof(original_data));
     expect(validator_recv_frame,
         when(size, is_equal_to(sizeof(original_data))),
         when(data, is_equal_to_contents_of(original_data, sizeof(original_data)))
     );
     for(i=0;i<sent_data_size;i++) {
-       recv_byte(sent_data[i]);
+       recv_byte(1, sent_data[i]);
     }
 }
 
@@ -478,13 +478,13 @@ Ensure(ByteStuffer, sends_and_receives_full_roundtrip_256_bytes) {
     }
     original_data[254] = 22;
     original_data[255] = 23;
-    send_frame(original_data, sizeof(original_data));
+    send_frame(0, original_data, sizeof(original_data));
     expect(validator_recv_frame,
         when(size, is_equal_to(sizeof(original_data))),
         when(data, is_equal_to_contents_of(original_data, sizeof(original_data)))
     );
     for(i=0;i<sent_data_size;i++) {
-       recv_byte(sent_data[i]);
+       recv_byte(1, sent_data[i]);
     }
 }
 
@@ -495,12 +495,12 @@ Ensure(ByteStuffer, sends_and_receives_full_roundtrip_254_bytes_and_then_zero) {
         original_data[i] = i + 1;
     }
     original_data[254] = 0;
-    send_frame(original_data, sizeof(original_data));
+    send_frame(0, original_data, sizeof(original_data));
     expect(validator_recv_frame,
         when(size, is_equal_to(sizeof(original_data))),
         when(data, is_equal_to_contents_of(original_data, sizeof(original_data)))
     );
     for(i=0;i<sent_data_size;i++) {
-       recv_byte(sent_data[i]);
+       recv_byte(1, sent_data[i]);
     }
 }
diff --git a/serial_link/tests/frame_validator_tests.c b/serial_link/tests/frame_validator_tests.c
index 6f9b746f..49c61d1e 100644
--- a/serial_link/tests/frame_validator_tests.c
+++ b/serial_link/tests/frame_validator_tests.c
@@ -26,11 +26,11 @@ SOFTWARE.
 #include <cgreen/mocks.h>
 #include "protocol/frame_validator.c"
 
-void route_incoming_frame(uint8_t* data, uint16_t size) {
+void route_incoming_frame(uint8_t link, uint8_t* data, uint16_t size) {
     mock(data, size);
 }
 
-void send_frame(uint8_t* data, uint16_t size) {
+void send_frame(uint8_t link, uint8_t* data, uint16_t size) {
     mock(data, size);
 }
 
@@ -41,10 +41,10 @@ AfterEach(FrameValidator) {}
 Ensure(FrameValidator, doesnt_validate_frames_under_5_bytes) {
     never_expect(route_incoming_frame);
     uint8_t data[] = {1, 2};
-    validator_recv_frame(0, 1);
-    validator_recv_frame(data, 2);
-    validator_recv_frame(data, 3);
-    validator_recv_frame(data, 4);
+    validator_recv_frame(0, 0, 1);
+    validator_recv_frame(0, data, 2);
+    validator_recv_frame(0, data, 3);
+    validator_recv_frame(0, data, 4);
 }
 
 Ensure(FrameValidator, validates_one_byte_frame_with_correct_crc) {
@@ -53,13 +53,13 @@ Ensure(FrameValidator, validates_one_byte_frame_with_correct_crc) {
         when(size, is_equal_to(1)),
         when(data, is_equal_to_contents_of(data, 1))
     );
-    validator_recv_frame(data, 5);
+    validator_recv_frame(0, data, 5);
 }
 
 Ensure(FrameValidator, does_not_validate_one_byte_frame_with_incorrect_crc) {
     uint8_t data[] = {0x44, 0, 0, 0, 0};
     never_expect(route_incoming_frame);
-    validator_recv_frame(data, 5);
+    validator_recv_frame(1, data, 5);
 }
 
 Ensure(FrameValidator, validates_four_byte_frame_with_correct_crc) {
@@ -68,7 +68,7 @@ Ensure(FrameValidator, validates_four_byte_frame_with_correct_crc) {
         when(size, is_equal_to(4)),
         when(data, is_equal_to_contents_of(data, 4))
     );
-    validator_recv_frame(data, 8);
+    validator_recv_frame(1, data, 8);
 }
 
 Ensure(FrameValidator, validates_five_byte_frame_with_correct_crc) {
@@ -77,7 +77,7 @@ Ensure(FrameValidator, validates_five_byte_frame_with_correct_crc) {
         when(size, is_equal_to(5)),
         when(data, is_equal_to_contents_of(data, 5))
     );
-    validator_recv_frame(data, 9);
+    validator_recv_frame(0, data, 9);
 }
 
 Ensure(FrameValidator, sends_one_byte_with_correct_crc) {
@@ -87,7 +87,7 @@ Ensure(FrameValidator, sends_one_byte_with_correct_crc) {
         when(size, is_equal_to(sizeof(expected))),
         when(data, is_equal_to_contents_of(expected, sizeof(expected)))
     );
-    validator_send_frame(original, 1);
+    validator_send_frame(0, original, 1);
 }
 
 Ensure(FrameValidator, sends_five_bytes_with_correct_crc) {
@@ -97,5 +97,5 @@ Ensure(FrameValidator, sends_five_bytes_with_correct_crc) {
         when(size, is_equal_to(sizeof(expected))),
         when(data, is_equal_to_contents_of(expected, sizeof(expected)))
     );
-    validator_send_frame(original, 5);
+    validator_send_frame(0, original, 5);
 }