diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1cc93ac..2ee1ba5 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -285,6 +285,11 @@ set(DEVICE_SOURCES
   ${PROJECT_SOURCE_DIR}/device/sha1.c
 )
 
+set(GDB_SOURCES
+  ${PROJECT_SOURCE_DIR}/gdb/gdb.c
+  ${PROJECT_SOURCE_DIR}/gdb/protocol.c
+)
+
 set(OS_SOURCES
   ${PROJECT_SOURCE_DIR}/os/common/gl_hints.c
   ${PROJECT_SOURCE_DIR}/os/common/input.c
@@ -438,6 +443,7 @@ add_executable(cen64
   ${COMMON_SOURCES}
   ${DD_SOURCES}
   ${DEVICE_SOURCES}
+  ${GDB_SOURCES}
   ${OS_SOURCES}
   ${PI_SOURCES}
   ${RDP_SOURCES}
diff --git a/cen64.c b/cen64.c
index c8e1385..0aa7ec3 100644
--- a/cen64.c
+++ b/cen64.c
@@ -16,6 +16,7 @@
 #include "device/options.h"
 #include "device/sha1.h"
 #include "device/sha1_sums.h"
+#include "gdb/gdb.h"
 #include "os/common/alloc.h"
 #include "os/common/rom_file.h"
 #include "os/common/save_file.h"
@@ -179,6 +180,8 @@ int cen64_main(int argc, const char **argv) {
     }
   }
 
+
+
   // Allocate memory for and create the device.
   if (cen64_alloc(&cen64_device_mem, sizeof(*device), false) == NULL) {
     printf("Failed to allocate enough memory for a device.\n");
@@ -197,9 +200,20 @@ int cen64_main(int argc, const char **argv) {
     }
 
     else {
+      struct gdb* debugger = NULL;
+
+      if (options.debugger_addr) {
+        debugger = gdb_alloc();
+        gdb_init(debugger, device, options.debugger_addr);
+      }
+
       device->multithread = options.multithread;
       status = run_device(device, options.no_video);
       device_destroy(device, options.cart_path);
+
+      if (debugger) {
+        gdb_destroy(debugger);
+      }
     }
 
     cen64_free(&cen64_device_mem);
diff --git a/gdb/gdb.c b/gdb/gdb.c
new file mode 100644
index 0000000..021784d
--- /dev/null
+++ b/gdb/gdb.c
@@ -0,0 +1,260 @@
+//
+// gdb.c: gdb remote debugger implementation
+//
+// CEN64: Cycle-Accurate Nintendo 64 Emulator.
+// Copyright (C) 2015, Tyler J. Stachecki.
+//
+// This file is subject to the terms and conditions defined in
+// 'LICENSE', which is part of this source code package.
+//
+
+#include "gdb/gdb.h"
+#include "gdb/protocol.h"
+
+#ifdef _WIN32
+#include <winsock2.h>
+#include <windows.h>
+#include <ws2tcpip.h>
+#else
+#include <netdb.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <unistd.h>
+#endif
+
+cen64_cold void gdb_handle_breakpoint(void* data, enum vr4300_debug_break_reason reason);
+
+int gdb_read(struct gdb* gdb) {
+  if (gdb->pending_data >= MAX_GDB_PACKET_SIZE) {
+    // if the gdb client is well behaved this should never happen
+    gdb->pending_data = 0;
+  }
+
+  int bytes_read = recv(gdb->client, gdb->packet_buffer + gdb->pending_data, MAX_GDB_PACKET_SIZE, 0);
+
+  if (bytes_read > 0) {
+    gdb->pending_data += bytes_read;
+  }
+  
+
+  return bytes_read;
+}
+
+void gdb_mark_read(struct gdb* gdb, int handled_bytes) {
+  if (handled_bytes <= gdb->pending_data) {
+    gdb->pending_data -= handled_bytes;
+  } else {
+    gdb->pending_data = 0;
+  }
+
+  if (gdb->pending_data) {
+    for (int i = 0; i < gdb->pending_data; i++) {
+      gdb->packet_buffer[i] = gdb->packet_buffer[i + handled_bytes];
+    }
+  }
+}
+
+bool gdb_parse_packet(const char* input, int len, const char** command_start, const char** command_end) {
+    const char* string_end = input + len;
+
+    while (input < string_end) {
+        if (*input == '$') {
+            input++;
+            *command_start = input;
+            break;
+        }
+        input++;
+    }
+
+    while (input < string_end) {
+        if (*input == '#') {
+            *command_end = input;
+            return true;
+        } else {
+            input++;
+        }
+    }
+
+    return false;
+}
+
+CEN64_THREAD_RETURN_TYPE gdb_thread(void *opaque) {
+  cen64_thread_setname(NULL, "gdb");
+  struct gdb *gdb = (struct gdb *) opaque;
+
+  cen64_mutex_lock(&gdb->client_mutex);
+
+  // wait until first breakpoint is hit before entering loop
+  if (gdb->flags & GDB_FLAGS_INITIAL) {
+    cen64_cv_wait(&gdb->client_semaphore, &gdb->client_mutex);
+  } else {
+    cen64_mutex_lock(&gdb->client_mutex);
+  }
+
+  while (gdb->flags & GDB_FLAGS_CONNECTED) {
+    int bytes_read = gdb_read(gdb);
+
+    debug("rec: %.*s\n", bytes_read, gdb->packet_buffer + gdb->pending_data - bytes_read);
+
+    if (bytes_read <= 0) {
+      gdb->flags &= ~GDB_FLAGS_CONNECTED;
+      printf("Debug socket closed\n");
+      break;
+    }
+
+    const char* command_start;
+    const char* command_end;
+
+    bool did_handle = false;
+
+    do {
+      int handled_bytes = 0;
+
+      int search_end = gdb->pending_data;
+
+      if (gdb_parse_packet(gdb->packet_buffer, gdb->pending_data, &command_start, &command_end)) {
+        send(gdb->client, "+", strlen("+"), 0);
+        gdb_handle_packet(gdb, command_start, command_end);
+        
+        // +3, 1 byte for the '#' and 2 additional bytes for the checksum
+        handled_bytes = (command_end - gdb->packet_buffer) + 3;
+        search_end = command_start - gdb->packet_buffer;
+      }
+
+      int at;
+
+      for (at = 0; at < search_end && gdb->packet_buffer[at] != '$'; at++) {
+        if (gdb->packet_buffer[at] == 0x03) {
+          vr4300_signal_break(gdb->device->vr4300);
+        }
+      }
+
+      if (at > handled_bytes) {
+        handled_bytes = at;
+      }
+
+      bytes_read -= handled_bytes;
+      gdb_mark_read(gdb, handled_bytes);
+    } while (did_handle);
+
+  }
+
+  return CEN64_THREAD_RETURN_VAL;
+}
+
+cen64_cold void gdb_handle_breakpoint(void* data, enum vr4300_debug_break_reason reason) {
+  struct gdb* gdb = (struct gdb*)data;
+
+  debug("Stopping at 0x%08x\n", (uint32_t)vr4300_get_pc(gdb->device->vr4300));
+
+  if (!(gdb->flags & GDB_FLAGS_CONNECTED)) {
+    return;
+  } else if (gdb->flags & GDB_FLAGS_INITIAL) {
+    gdb->flags &= ~GDB_FLAGS_INITIAL;
+    vr4300_remove_breakpoint(gdb->device->vr4300, 0xFFFFFFFF80000000ULL);
+    cen64_cv_signal(&gdb->client_semaphore);
+  } else {
+    gdb_send_stop_reply(gdb, reason == VR4300_DEBUG_BREAK_REASON_BREAKPOINT);
+  }
+
+  cen64_mutex_lock(&gdb->client_mutex);
+  gdb->flags |= GDB_FLAGS_PAUSED;
+  cen64_cv_wait(&gdb->client_semaphore, &gdb->client_mutex);
+  gdb->flags &= ~GDB_FLAGS_PAUSED;
+
+  if (!(gdb->flags & GDB_FLAGS_CONNECTED)) {
+    vr4300_connect_debugger(gdb->device->vr4300, NULL, NULL);
+  }
+}
+
+cen64_cold struct gdb* gdb_alloc() {
+    struct gdb* result = malloc(sizeof(struct gdb));
+    memset(result, 0, sizeof(struct gdb));
+    return result;
+}
+
+cen64_cold bool gdb_init(struct gdb* gdb, struct cen64_device* device, const char* host) {
+  int port;
+  if (sscanf(host, "localhost:%d", &port) != 1) {
+    printf("debugger error: -debug flag must be followed by locahost:<port number>\n");
+    return false;
+  }
+
+  if (port < 0 || port > 0xffff) {
+    printf("debugger error: -debug port must be a value between 0-65535\n");
+    return false;
+  }
+
+  if ((gdb->socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0) {
+    printf("debugger error: could create socket\n");
+    return false;
+  }
+  struct sockaddr_in addr;
+  memset(&addr, 0, sizeof(addr));
+  addr.sin_family = AF_INET;
+  //addr.sin_addr.s_addr = IPADDR_ANY;
+  addr.sin_port = htons((unsigned short)port);
+
+  int flag = 1;  
+  if (-1 == setsockopt(gdb->socket, SOL_SOCKET, SO_REUSEADDR, &flag, sizeof(flag))) {
+    printf("debugger error: could not open port %d\n", (int)port);
+    return false;
+  }
+
+  if(bind(gdb->socket, (struct sockaddr*)&addr, sizeof(addr)) < 0) {
+    printf("debugger error: could not open port %d\n", (int)port);
+    return false;
+  }
+
+  if(listen(gdb->socket, 1) < 0) {
+    printf("debugger error: could not listen on port %d\n", (int)port);
+    return false;
+  }
+
+  printf("Waiting for gdb connection on port %d\n", (int)port);
+
+  if((gdb->client = accept(gdb->socket, NULL, NULL)) < 0) {
+    printf("debugger error: could not connect to client on port %d\n", (int)port);
+    return false;
+  }
+
+  gdb->device = device;
+  device_connect_debugger(device, gdb, &gdb_handle_breakpoint);
+
+  gdb->flags = GDB_FLAGS_INITIAL | GDB_FLAGS_CONNECTED;
+  vr4300_set_breakpoint(device->vr4300, 0xFFFFFFFF80000000ULL);
+
+  if (cen64_mutex_create(&gdb->client_mutex)) {
+    printf("Failed to create gdb client semaphore.\n");
+    return false;
+  }
+
+  if (cen64_cv_create(&gdb->client_semaphore)) {
+    cen64_mutex_destroy(&gdb->client_mutex);
+    printf("Failed to create gdb client semaphore.\n");
+    return false;
+  }
+
+  if (cen64_thread_create(&gdb->thread, gdb_thread, gdb)) {
+    cen64_mutex_destroy(&gdb->client_mutex);
+    cen64_cv_destroy(&gdb->client_semaphore);
+    printf("Failed to create gdb thread.\n");
+    return false;
+  }
+
+  return true;
+}
+
+cen64_cold void gdb_destroy(struct gdb* gdb) {
+  gdb->flags = 0;
+
+  shutdown(gdb->client, 2);
+  shutdown(gdb->socket, 2);
+
+  cen64_thread_join(&gdb->thread);
+  cen64_mutex_destroy(&gdb->client_mutex);
+  cen64_cv_destroy(&gdb->client_semaphore);
+
+  gdb->device = NULL;
+  free(gdb);
+}
\ No newline at end of file
diff --git a/gdb/gdb.h b/gdb/gdb.h
new file mode 100644
index 0000000..cd71630
--- /dev/null
+++ b/gdb/gdb.h
@@ -0,0 +1,42 @@
+//
+// gdb.h: gdb remote debugger implementation
+//
+// CEN64: Cycle-Accurate Nintendo 64 Emulator.
+// Copyright (C) 2015, Tyler J. Stachecki.
+//
+// This file is subject to the terms and conditions defined in
+// 'LICENSE', which is part of this source code package.
+//
+
+#ifndef _gdb_h__
+#define _gdb_h__
+#include "common.h"
+#include "vr4300/interface.h"
+#include "device/device.h"
+
+#define MAX_GDB_PACKET_SIZE     0x4000
+
+enum gdb_flags {
+    GDB_FLAGS_INITIAL = 0x1,
+    GDB_FLAGS_CONNECTED = 0x2,
+    GDB_FLAGS_PAUSED = 0x4,
+};
+
+struct gdb {
+    int socket;
+    int client;
+    struct cen64_device* device;
+    int pending_data;
+    char packet_buffer[MAX_GDB_PACKET_SIZE*2];
+    char output_buffer[MAX_GDB_PACKET_SIZE];
+    int flags;
+    cen64_thread thread;
+    cen64_mutex client_mutex;
+    cen64_cv client_semaphore;
+};
+
+cen64_cold struct gdb* gdb_alloc();
+cen64_cold bool gdb_init(struct gdb* gdb, struct cen64_device* device, const char* host);
+cen64_cold void gdb_destroy(struct gdb* gdb);
+
+#endif
\ No newline at end of file
diff --git a/gdb/protocol.c b/gdb/protocol.c
new file mode 100644
index 0000000..cd680e8
--- /dev/null
+++ b/gdb/protocol.c
@@ -0,0 +1,351 @@
+//
+// protocol.c: gdb message parsing and responding
+//
+// CEN64: Cycle-Accurate Nintendo 64 Emulator.
+// Copyright (C) 2015, Tyler J. Stachecki.
+//
+// This file is subject to the terms and conditions defined in
+// 'LICENSE', which is part of this source code package.
+//
+
+#include "gdb/protocol.h"
+#include "gdb/gdb.h"
+#include "vr4300/cpu.h"
+
+#include <inttypes.h>
+
+#ifdef _WIN32
+#include <winsock2.h>
+#include <windows.h>
+#include <ws2tcpip.h>
+#else
+#include <netdb.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <unistd.h>
+#endif
+
+#define GDB_GET_EXC_CODE(cause) (((cause) >> 2) & 0x1f)
+#define GDB_TRANSLATE_PC(pc)    ((uint64_t)(pc) | 0xFFFFFFFF00000000ULL)
+#define GDB_GLOBAL_THREAD_ID 1
+#define GDB_STR_STARTS_WITH(str, const_str) (strncmp(str, const_str, sizeof const_str - 1) == 0)
+
+static int gdb_signals[32] = {
+  2, // SIGINT
+  11, // SIGSEGV
+  11, // SIGSEGV
+  11, // SIGSEGV
+  11, // SIGSEGV
+  11, // SIGSEGV
+  10, // SIGBUS
+  10, // SIGBUS
+  12, // SIGSYS
+  5, // SIGTRAP
+  4, // SIGILL
+  30, // SIGUSR1
+  8, // SIGFPE
+  5, // SIGTRAP
+  0, // reserved
+  8, // SIGFPE
+  0, // reserved
+  0, // reserved
+  0, // reserved
+  0, // reserved
+  0, // reserved
+  0, // reserved
+  0, // reserved
+  5, // SIGTRAP
+  0, // reserved
+  0, // reserved
+  0, // reserved
+  0, // reserved
+  0, // reserved
+  0, // reserved
+  0, // reserved
+  0, // reserved
+};
+
+int gdb_read_hex_digit(char character) {
+  if (character >= 'a' && character <= 'f') {
+    return 10 + character - 'a';
+  } else if (character >= 'A' && character <= 'F') {
+    return 10 + character - 'A';
+  } else if (character >= '0' && character <= '9') {
+    return character - '0';
+  } else {
+    return -1;
+  }   
+}
+
+uint32_t gdb_parse_hex(const char* src, int max_bytes) {
+  uint32_t result = 0;
+  int current_char;
+  int max_characters = max_bytes * 2;
+
+  for (current_char = 0; current_char < max_characters; ++current_char) {
+    int digit = gdb_read_hex_digit(*src);
+
+    if (digit != -1) {
+      result = (result << 4) + digit;
+    } else {
+      break;
+    }
+
+    ++src;
+  }
+
+  return result;
+}
+
+static char gdb_hex_letters[16] = "0123456789abcdef";
+
+char* gdb_write_hex64(char* target, uint64_t data, int data_size) {
+  int shift = data_size * 8 - 4;
+
+  while (shift >= 0) {
+    *target++ = gdb_hex_letters[(data >> shift) & 0xF];
+    shift -= 4;
+  }
+
+  return target;
+}
+
+int gdb_apply_checksum(char* message) {
+    char* message_start = message;
+    if (*message == '$') {
+        ++message;
+    }
+    
+    unsigned char checksum = 0;
+    while (*message)
+    {
+        if (*message == '#') {
+            ++message;
+            break;
+        }
+
+        checksum += (unsigned char)*message;
+        ++message;
+    }
+
+    sprintf(message, "%02x", checksum);
+
+    return (message - message_start) + 2;
+}
+
+void gdb_send(struct gdb* gdb) {
+  int messageLen = gdb_apply_checksum(gdb->output_buffer);
+  send(gdb->client, gdb->output_buffer, messageLen, 0);
+  debug("send: %.*s\n", messageLen, gdb->output_buffer);
+}
+
+void gdb_send_literal(struct gdb* gdb, const char* message) {
+    send(gdb->client, message, strlen(message), 0);
+    debug("send: %s\n", message);
+}
+
+void gdb_handle_query(struct gdb* gdb, const char* command_start, const char *command_end) {
+  if (GDB_STR_STARTS_WITH(command_start, "qSupported")) {
+    strcpy(gdb->output_buffer, "$PacketSize=4000;vContSupported+;swbreak+#");
+    gdb_send(gdb);
+  } else if (GDB_STR_STARTS_WITH(command_start, "qTStatus")) {
+    gdb_send_literal(gdb, "$#00");
+  } else if (GDB_STR_STARTS_WITH(command_start, "qfThreadInfo")) {
+    sprintf(gdb->output_buffer, "$m%x#", GDB_GLOBAL_THREAD_ID);
+    gdb_send(gdb);
+  } else if (GDB_STR_STARTS_WITH(command_start, "qsThreadInfo")) {
+    strcpy(gdb->output_buffer, "$l#");
+    gdb_send(gdb);
+  } else if (GDB_STR_STARTS_WITH(command_start, "qAttached")) {
+    strcpy(gdb->output_buffer, "$0#");
+    gdb_send(gdb);
+  } else if (GDB_STR_STARTS_WITH(command_start, "qC")) {
+    sprintf(gdb->output_buffer, "$QC%x#", GDB_GLOBAL_THREAD_ID);
+    gdb_send(gdb);
+  } else if (GDB_STR_STARTS_WITH(command_start, "qTfV")) {
+    gdb_send_literal(gdb, "$#00");
+  } else if (GDB_STR_STARTS_WITH(command_start, "qTfP")) {
+    gdb_send_literal(gdb, "$#00");
+  } else if (GDB_STR_STARTS_WITH(command_start, "qOffsets")) {
+    sprintf(gdb->output_buffer, "$Text=%x;Data=%x;Bss=%x#", 0, 0, 0);
+    gdb_send(gdb);
+  } else if (GDB_STR_STARTS_WITH(command_start, "qSymbol")) {
+    gdb_send_literal(gdb, "$OK#9a");
+  } else if (GDB_STR_STARTS_WITH(command_start, "qThreadExtraInfo")) {
+    strcpy(gdb->output_buffer, "$746872656164#");
+    gdb_send(gdb);
+  } else {
+    gdb_send_literal(gdb, "$#00");
+  }
+}
+
+void gdb_handle_v(struct gdb* gdb, const char* command_start, const char *command_end) {
+  if (GDB_STR_STARTS_WITH(command_start, "vMustReplyEmpty")) {
+    gdb_send_literal(gdb, "$#00");
+  } else if (GDB_STR_STARTS_WITH(command_start, "vCont")) {
+    if (command_start[5] == '?') {
+      strcpy(gdb->output_buffer, "$c;t#");
+      gdb_send(gdb);
+    } else {
+      switch (command_start[6])
+      {
+        case 'c':
+          cen64_cv_signal(&gdb->client_semaphore);
+          break;
+        case 't':
+          vr4300_signal_break(gdb->device->vr4300);
+          break;
+      }
+    }
+  } else if (GDB_STR_STARTS_WITH(command_start, "vKill")) {
+    gdb->flags &= ~GDB_FLAGS_CONNECTED;
+    gdb->flags &= ~GDB_FLAGS_PAUSED;
+    cen64_cv_signal(&gdb->client_semaphore);
+    gdb_send_literal(gdb, "$OK#9a");
+  } else {
+    gdb_send_literal(gdb, "$#00");
+  }
+}
+
+void gdb_reply_registers(struct gdb* gdb) {
+  char* current = gdb->output_buffer;
+  *current++ = '$';
+
+  // R0
+  current = gdb_write_hex64(current, 0, sizeof(uint64_t));
+  for (int i = VR4300_REGISTER_AT; i <= VR4300_REGISTER_RA; i++) {
+    current = gdb_write_hex64(current, vr4300_get_register(gdb->device->vr4300, i), sizeof(uint64_t));
+  }
+
+  current = gdb_write_hex64(current, vr4300_get_register(gdb->device->vr4300, VR4300_CP0_REGISTER_STATUS), sizeof(uint64_t));
+  current = gdb_write_hex64(current, vr4300_get_register(gdb->device->vr4300, VR4300_REGISTER_LO), sizeof(uint64_t));
+  current = gdb_write_hex64(current, vr4300_get_register(gdb->device->vr4300, VR4300_REGISTER_HI), sizeof(uint64_t));
+  current = gdb_write_hex64(current, vr4300_get_register(gdb->device->vr4300, VR4300_CP0_REGISTER_BADVADDR), sizeof(uint64_t));
+  current = gdb_write_hex64(current, vr4300_get_register(gdb->device->vr4300, VR4300_CP0_REGISTER_CAUSE), sizeof(uint64_t));
+  current += sprintf(current, "%08x%08x", 0, (int32_t)vr4300_get_pc(gdb->device->vr4300));
+
+  for (int i = VR4300_REGISTER_CP1_0; i <= VR4300_REGISTER_CP1_31; i++) {
+    current = gdb_write_hex64(current, vr4300_get_register(gdb->device->vr4300, i), sizeof(uint64_t));
+  }
+
+  current = gdb_write_hex64(current, vr4300_get_register(gdb->device->vr4300, VR4300_CP1_FCR31), sizeof(uint64_t));
+
+  *current++ = '#';
+  *current++ = '\0';
+
+  gdb_send(gdb);
+}
+
+void gdb_reply_memory(struct gdb* gdb, const char* command_start, const char *command_end) {
+  char* current = gdb->output_buffer;
+  *current++ = '$';
+
+  const char* len_text = command_start + 1;
+
+  while (*len_text != ',' && len_text != command_end) {
+      ++len_text;
+  }
+
+  int32_t addr = gdb_parse_hex(command_start + 1, 4);
+  int32_t len = gdb_parse_hex(len_text + 1, 4);
+
+  int32_t alignedAddr = addr & ~0x3;
+  int32_t byteShift = addr - alignedAddr;
+    
+  for (int curr = 0; curr < len + byteShift; curr += 4) {
+    uint32_t word = 0;
+    int32_t vaddr = alignedAddr + curr;
+    
+    if (!vr4300_read_word_vaddr(gdb->device->vr4300, vaddr, &word)) {
+      debug("Bad vaddr %08x\n", vaddr);
+    }
+
+    // if (curr > 0x20) {
+    //   word = curr;
+    // }
+
+    current = gdb_write_hex64(current, word, sizeof(uint32_t));
+  }
+
+  if (byteShift) {
+    for (int curr = 0; curr < len * 2; curr++) {
+      gdb->output_buffer[curr + 1] = gdb->output_buffer[curr + 1 + byteShift * 2];
+    }
+  }
+
+  current = gdb->output_buffer + 1 + len * 2;
+
+  *current++ = '#';
+  *current++ = '\0';
+
+  gdb_send(gdb);
+}
+
+void gdb_handle_packet(struct gdb* gdb, const char* command_start, const char* command_end) {
+  switch (*command_start) {
+    case 'q':
+      gdb_handle_query(gdb, command_start, command_end);
+      break;
+    case 'v':
+      gdb_handle_v(gdb, command_start, command_end);
+      break;
+    case 'H':
+      gdb_send_literal(gdb, "$OK#9a");
+      break;
+    case '!':
+      gdb_send_literal(gdb, "$#00");
+      break;
+    case '?':
+      gdb_send_stop_reply(gdb, false);
+      break;
+    case 'g':
+      gdb_reply_registers(gdb);
+      break;
+    case 'm':
+      gdb_reply_memory(gdb, command_start, command_end);
+      break;
+    case 'D':
+      gdb->flags &= ~GDB_FLAGS_CONNECTED;
+      gdb_send_literal(gdb, "$OK#9a");;
+      break;
+    case 'z':
+    case 'Z':
+    {
+      if (command_start[1] == '0') {
+        uint64_t addr = GDB_TRANSLATE_PC(gdb_parse_hex(&command_start[3], 4));
+
+        if (*command_start == 'z') {
+          vr4300_remove_breakpoint(gdb->device->vr4300, addr);
+        } else {
+          vr4300_set_breakpoint(gdb->device->vr4300, addr);
+        }
+
+        return gdb_send_literal(gdb, "$OK#9a");
+      } else {
+        gdb_send_literal(gdb, "$#00");
+      }
+      break;
+    }
+    default:
+      gdb_send_literal(gdb, "$#00");
+  }
+}
+
+cen64_cold void gdb_send_stop_reply(struct gdb* gdb, bool is_breakpoint) {
+  char* current = gdb->output_buffer;
+  int exc_code;
+
+  if (is_breakpoint) {
+    exc_code = 9;
+  } else {
+    exc_code = GDB_GET_EXC_CODE(vr4300_get_register(gdb->device->vr4300, VR4300_CP0_REGISTER_CAUSE));
+  }
+  current += sprintf(current, "$T%02x", gdb_signals[exc_code]);
+  if (is_breakpoint) {
+    current += sprintf(current, "swbreak:");
+  }
+  current += sprintf(current, "thread:%d;", GDB_GLOBAL_THREAD_ID);
+  *current++ = '#';
+  *current++ = '\0';
+  gdb_send(gdb);
+}
\ No newline at end of file
diff --git a/gdb/protocol.h b/gdb/protocol.h
new file mode 100644
index 0000000..c6c6075
--- /dev/null
+++ b/gdb/protocol.h
@@ -0,0 +1,21 @@
+//
+// protocol.h: gdb message parsing and responding
+//
+// CEN64: Cycle-Accurate Nintendo 64 Emulator.
+// Copyright (C) 2015, Tyler J. Stachecki.
+//
+// This file is subject to the terms and conditions defined in
+// 'LICENSE', which is part of this source code package.
+//
+
+#ifndef _gdb_protocol_h__
+#define _gdb_protocol_h__
+#include "common.h"
+
+struct gdb;
+
+cen64_cold void gdb_send_stop_reply(struct gdb* gdb, bool is_breakpoint);
+cen64_cold void gdb_handle_packet(struct gdb* gdb, const char* command_start, const char* command_end);
+
+
+#endif