diff --git a/src/uxn.c b/src/uxn.c
index 7fcd754..2037f66 100644
--- a/src/uxn.c
+++ b/src/uxn.c
@@ -116,7 +116,7 @@ timeout:
 /* clang-format on */
 
 int
-uxn_boot(Uxn *u, Uint8 *ram)
+uxn_boot(Uxn *u, Uint8 *ram, Dei *dei, Deo *deo)
 {
 	Uint32 i;
 	char *cptr = (char *)u;
diff --git a/src/uxn.h b/src/uxn.h
index dd39bb2..183f8ca 100644
--- a/src/uxn.h
+++ b/src/uxn.h
@@ -49,9 +49,14 @@ typedef struct Uxn {
 	Uint8 *ram;
 	Stack wst, rst;
 	Device dev[16];
+	Uint8 (*dei)(struct Uxn *u, Uint8 addr);
+	void (*deo)(struct Uxn *u, Uint8 addr, Uint8 value);
 } Uxn;
 
-int uxn_boot(Uxn *u, Uint8 *ram);
+typedef Uint8 Dei(Uxn *u, Uint8 addr);
+typedef void Deo(Uxn *u, Uint8 addr, Uint8 value);
+
+int uxn_boot(Uxn *u, Uint8 *ram, Dei *dei, Deo *deo);
 int uxn_eval(Uxn *u, Uint16 pc);
 int uxn_interrupt(void);
 int uxn_halt(Uxn *u, Uint8 error, Uint16 addr);
diff --git a/src/uxncli.c b/src/uxncli.c
index 1c2ccda..0678fdd 100644
--- a/src/uxncli.c
+++ b/src/uxncli.c
@@ -24,6 +24,17 @@ error(char *msg, const char *err)
 	return 0;
 }
 
+static Uint8
+emu_dei(Uxn *u, Uint8 addr)
+{
+	return 0;
+}
+
+static void
+emu_deo(Uxn *u, Uint8 addr, Uint8 v)
+{
+}
+
 void
 system_deo_special(Device *d, Uint8 port)
 {
@@ -83,7 +94,7 @@ uxn_interrupt(void)
 static int
 start(Uxn *u)
 {
-	if(!uxn_boot(u, (Uint8 *)calloc(0x10000, sizeof(Uint8))))
+	if(!uxn_boot(u, (Uint8 *)calloc(0x10000, sizeof(Uint8)), emu_dei, emu_deo))
 		return error("Boot", "Failed");
 	/* system   */ uxn_port(u, 0x0, system_dei, system_deo);
 	/* console  */ uxn_port(u, 0x1, nil_dei, console_deo);
diff --git a/src/uxnemu.c b/src/uxnemu.c
index 0aafa8a..3eb3c25 100644
--- a/src/uxnemu.c
+++ b/src/uxnemu.c
@@ -176,6 +176,17 @@ init(void)
 
 #pragma mark - Devices
 
+static Uint8
+emu_dei(Uxn *u, Uint8 addr)
+{
+	return 0;
+}
+
+static void
+emu_deo(Uxn *u, Uint8 addr, Uint8 v)
+{
+}
+
 void
 system_deo_special(Device *d, Uint8 port)
 {
@@ -253,7 +264,7 @@ static int
 start(Uxn *u, char *rom)
 {
 	free(u->ram);
-	if(!uxn_boot(u, calloc(0x10000, 1)))
+	if(!uxn_boot(u, calloc(0x10000, 1), emu_dei, emu_deo))
 		return error("Boot", "Failed to start uxn.");
 	if(!load(u, rom))
 		return error("Boot", "Failed to load rom.");