diff --git a/lib/audio.c b/lib/audio.c
index bfa7c7f..856855e 100644
--- a/lib/audio.c
+++ b/lib/audio.c
@@ -413,8 +413,9 @@ void audio_tick(){
             }
         }
 
-        if(ctx.ch4_len_enable) {
+        if(ctx.ch4_len_enable && ctx.ch4_enable) {
             ctx.ch4_len++;
+            printf("Ch4 env: %02X\n", ctx.ch4_len);
             if(ctx.ch4_len >= 64) {
                 ctx.ch4_len = 0;
                 ctx.ch4_enable = false;
@@ -926,6 +927,7 @@ void audio_write(u16 address, u8 value){
         ctx.ch4_initial_len = value & 0b111111;
         ctx.ch4_len = ctx.ch4_initial_len;
         ctx.ch4_len_fz = false;
+        printf("ch4 len: %02X\n", ctx.ch4_len);
     }
 
     if(address == 0xFF21) {
@@ -969,6 +971,7 @@ void audio_write(u16 address, u8 value){
             }
         }
         ctx.ch4_len_enable = len_en;
+        printf("ch4 trigger: LenEn %d\n", len_en);
         if(value & 0x80) {
             enable_noise();
         }
diff --git a/lib/cart.c b/lib/cart.c
index 0c66186..45d942f 100644
--- a/lib/cart.c
+++ b/lib/cart.c
@@ -36,8 +36,16 @@ bool cart_mbc1() {
     return BETWEEN(ctx.header->type, 1, 3);
 }
 
+bool cart_mbc3() {
+    return BETWEEN(ctx.header->type, 15, 19);
+}
+
+bool cart_mbc() {
+    return cart_mbc1() || cart_mbc3();
+}
+
 bool cart_battery() {
-    return ctx.header->type == 3;
+    return ctx.header->type == 3 || BETWEEN(ctx.header->type, 15, 16) || ctx.header->type == 19;
 }
 
 static const char *ROM_TYPES[] = {
@@ -232,7 +240,7 @@ bool cart_load(char *cart) {
 }
 
 u8 cart_read(u16 address){
-    if(!cart_mbc1() || address < 0x4000) {
+    if(!cart_mbc() || address < 0x4000) {
         return ctx.rom_data[address];
     }
 
@@ -253,7 +261,8 @@ u8 cart_read(u16 address){
 }
 
 void cart_write(u16 address, u8 value){
-    if(!cart_mbc1()) {
+    //printf("Cart Write: %04X\n", address);
+    if(!cart_mbc()) {
         return;
     }
 
@@ -266,10 +275,15 @@ void cart_write(u16 address, u8 value){
         if(value == 0) {
             value = 1;
         }
-
-        value &= 0b11111;
-        ctx.rom_bank_value = value;
-        ctx.rom_bank_x = ctx.rom_data + (0x4000 * ctx.rom_bank_value);
+        if(cart_mbc3()) {
+            value &= 0b1111111;
+            ctx.rom_bank_value = value;
+            ctx.rom_bank_x = ctx.rom_data + (0x4000 * ctx.rom_bank_value);
+        }else {
+            value &= 0b11111;
+            ctx.rom_bank_value = value;
+            ctx.rom_bank_x = ctx.rom_data + (0x4000 * ctx.rom_bank_value);
+        }
     }
 
     if((address & 0xE000) == 0x4000) {
@@ -284,17 +298,18 @@ void cart_write(u16 address, u8 value){
     }
 
     if((address & 0xE000) == 0x6000) {
-        //bamking mode select
+        //banking mode select
+        if(cart_mbc1()){
+            ctx.banking_mode = value & 1;
 
-        ctx.banking_mode = value & 1;
+            ctx.ram_banking = ctx.banking_mode;
 
-        ctx.ram_banking = ctx.banking_mode;
-
-        if (ctx.ram_banking) {
-            if(cart_need_save) {
-                cart_battery_save();
+            if (ctx.ram_banking) {
+                if(cart_need_save) {
+                    cart_battery_save();
+                }
+                ctx.ram_bank = ctx.ram_banks[ctx.ram_bank_value];
             }
-            ctx.ram_bank = ctx.ram_banks[ctx.ram_bank_value];
         }
     }
 
diff --git a/lib/timer.c b/lib/timer.c
index a45a675..569ffb2 100644
--- a/lib/timer.c
+++ b/lib/timer.c
@@ -39,7 +39,7 @@ void timer_tick() {
         }
     }
 
-    if((prev_div & (1 << 12)) && (!(ctx.div & (1 << 12)))){
+    if((prev_div & (1 << 13)) && (!(ctx.div & (1 << 13)))){
         audio_tick();
     }