diff --git a/include/tabby/command.h b/include/tabby/command.h
index cf46f13..9829ee3 100644
--- a/include/tabby/command.h
+++ b/include/tabby/command.h
@@ -2,9 +2,9 @@
 #define _TABBY_COMMAND_H
 
 typedef enum tabby_command {
-    TABBY_COMMAND_SEND        = 0x01,
-    TABBY_COMMAND_CLOCK_MODE  = 0x02,
-    TABBY_COMMAND_CLOCK_SPEED = 0x03
+    TABBY_COMMAND_SEND         = 0x01,
+    TABBY_COMMAND_CLOCK_SOURCE = 0x02,
+    TABBY_COMMAND_CLOCK_SPEED  = 0x03
 };
 
 #endif /* _TABBY_COMMAND_H */
diff --git a/include/tabby/link.h b/include/tabby/link.h
index 57f8952..9c9aa79 100644
--- a/include/tabby/link.h
+++ b/include/tabby/link.h
@@ -1,19 +1,24 @@
 #ifndef _TABBY_LINK_H
 #define _TABBY_LINK_H
 
+#include <string.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <termios.h>
 #include <sys/types.h>
+#include <sys/ioctl.h>
 
 #include <tabby/clock.h>
 
-#define TABBY_LINK_BAUD 115200
+#define TABBY_LINK_BAUD B115200
 
 int tabby_link_open(const char *dev);
 
-void tabby_link_close(int fd);
+int tabby_link_close(int fd);
 
-int tabby_link_send(int fd, char *buf, size_t len);
+ssize_t tabby_link_send(int fd, char *buf, uint16_t len);
 
-ssize_t tabby_link_recv(int fd, char *buf, size_t len);
+ssize_t tabby_link_recv(int fd, char *buf, uint16_t len);
 
 int tabby_link_set_clock_source(int fd, tabby_clock_source source);
 
diff --git a/include/tabby/packet.h b/include/tabby/packet.h
index dc9420a..f94c2ae 100644
--- a/include/tabby/packet.h
+++ b/include/tabby/packet.h
@@ -1,9 +1,13 @@
 #ifndef _TABBY_PACKET_H
 #define _TABBY_PACKET_H
 
+#define TABBY_PACKET_MAX_LEN 65535
+
+#include <tabby/command.h>
+
 typedef struct _tabby_packet {
     uint16_t type,
-             value;
+             command;
 } tabby_packet;
 
 #endif /* _TABBY_PACKET_H */
diff --git a/src/link.c b/src/link.c
new file mode 100644
index 0000000..3df40b9
--- /dev/null
+++ b/src/link.c
@@ -0,0 +1,78 @@
+#include <tabby/link.h>
+
+int tabby_link_open(const char *dev) {
+    int fd;
+    struct termios attr;
+
+    if ((fd = open(device, O_RDWR | O_NOCTTY)) < 0) {
+        goto error_open;
+    }
+
+    if (fcntl(fd, F_SETFL) < 0) {
+        goto error_io;
+    }
+
+    attr.c_cflag = CS8 | CREAD;
+    attr.c_ispeed = TABBY_LINK_BAUD;
+    attr.c_ospeed = TABBY_LINK_BAUD;
+    attr.c_iflag  = IGNPAR;
+    attr.c_oflag  = 0;
+    attr.c_lflag  = 0;
+
+    attr.c_cc[VTIME] = 0;
+    attr.c_cc[VMIN]  = 1;
+
+    if (tcsetattr(fd, TCSANOW, &attr) < 0) {
+        goto error_io;
+    }
+
+    return fd;
+
+error_io:
+    close(fd);
+
+error_open:
+    return -1;
+}
+
+int tabby_link_close(int fd) {
+    return close(fd);
+}
+
+ssize_t tabby_link_send(int fd, char *buf, uint16_t len) {
+    tabby_packet header = {
+        .type  = htobe16(TABBY_COMMAND_SEND),
+        .value = htobe16(len)
+    };
+
+    if (write(fd, &header, sizeof(header)) < 0) {
+        goto error_write_header;
+    }
+
+    return write(fd, buf, (size_t)len);
+
+error_write_header:
+    return -1;
+}
+
+ssize_t tabby_link_recv(int fd, char *buf, uint16_t len) {
+    return read(fd, buf, (size_t)len);
+}
+
+int tabby_link_set_clock_source(int fd, tabby_clock_source source) {
+    tabby_packet packet = {
+        .command = htobe16(TABBY_COMMAND_CLOCK_SOURCE),
+        .value   = htobe16(source)
+    };
+
+    return write(fd, &packet, sizeof(packet));
+}
+
+int tabby_link_set_clock_speed(int fd, tabby_clock_speed speed) {
+    tabby_packet packet = {
+        .command = htobe16(TABBY_COMMAND_CLOCK_SPEED),
+        .value   = htobe16(speed)
+    };
+
+    return write(fd, &packet, sizeof(packet));
+}