diff --git a/extmod/machine_mem.c b/extmod/machine_mem.c
index 826c59d0f0..75496c6b5f 100644
--- a/extmod/machine_mem.c
+++ b/extmod/machine_mem.c
@@ -61,7 +61,7 @@ STATIC void machine_mem_print(const mp_print_t *print, mp_obj_t self_in, mp_prin
 }
 
 #pragma GCC diagnostic ignored "-Wunused-parameter"
-STATIC mp_obj_t machine_mem_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value, mp_obj_t instance) {
+STATIC mp_obj_t machine_mem_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
     // TODO support slice index to read/write multiple values at once
     machine_mem_obj_t *self = MP_OBJ_TO_PTR(self_in);
     if (value == MP_OBJ_NULL) {
diff --git a/extmod/modbtree.c b/extmod/modbtree.c
index 97a4de3d5b..ad845163d6 100644
--- a/extmod/modbtree.c
+++ b/extmod/modbtree.c
@@ -247,8 +247,9 @@ STATIC mp_obj_t btree_iternext(mp_obj_t self_in) {
 }
 
 #pragma GCC diagnostic ignored "-Wunused-parameter"
-STATIC mp_obj_t btree_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value, mp_obj_t instance) {
-    mp_obj_btree_t *self = MP_OBJ_TO_PTR(self_in);
+STATIC mp_obj_t btree_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
+    //mp_obj_btree_t *self = MP_OBJ_TO_PTR(self_in);
+    mp_obj_btree_t *self = mp_instance_cast_to_native_base(self_in, &btree_type);
     if (value == MP_OBJ_NULL) {
         // delete
         DBT key;
diff --git a/extmod/moductypes.c b/extmod/moductypes.c
index 722f4bb872..bf5f1cef73 100644
--- a/extmod/moductypes.c
+++ b/extmod/moductypes.c
@@ -519,8 +519,8 @@ STATIC void uctypes_struct_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
 }
 
 #pragma GCC diagnostic ignored "-Wunused-parameter"
-STATIC mp_obj_t uctypes_struct_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value, mp_obj_t instance) {
-    mp_obj_uctypes_struct_t *self = MP_OBJ_TO_PTR(self_in);
+STATIC mp_obj_t uctypes_struct_subscr(mp_obj_t base_in, mp_obj_t index_in, mp_obj_t value) {
+    mp_obj_uctypes_struct_t *self = mp_instance_cast_to_native_base(base_in, &uctypes_struct_type);
 
     if (value == MP_OBJ_NULL) {
         // delete
diff --git a/extmod/modurandom.c b/extmod/modurandom.c
index 101c80cf8a..1512a3fd4a 100644
--- a/extmod/modurandom.c
+++ b/extmod/modurandom.c
@@ -150,7 +150,7 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_urandom_randint_obj, mod_urandom_randint);
 STATIC mp_obj_t mod_urandom_choice(mp_obj_t seq) {
     mp_int_t len = mp_obj_get_int(mp_obj_len(seq));
     if (len > 0) {
-        return mp_obj_subscr(seq, mp_obj_new_int(yasmarang_randbelow(len)), MP_OBJ_SENTINEL, seq);
+        return mp_obj_subscr(seq, mp_obj_new_int(yasmarang_randbelow(len)), MP_OBJ_SENTINEL);
     } else {
         nlr_raise(mp_obj_new_exception(&mp_type_IndexError));
     }
diff --git a/extmod/vfs.c b/extmod/vfs.c
index 4d344095a6..2bb4057e7e 100644
--- a/extmod/vfs.c
+++ b/extmod/vfs.c
@@ -373,7 +373,7 @@ mp_obj_t mp_vfs_listdir(size_t n_args, const mp_obj_t *args) {
     mp_obj_t dir_list = mp_obj_new_list(0, NULL);
     mp_obj_t next;
     while ((next = mp_iternext(iter)) != MP_OBJ_STOP_ITERATION) {
-        mp_obj_list_append(dir_list, mp_obj_subscr(next, MP_OBJ_NEW_SMALL_INT(0), MP_OBJ_SENTINEL, next));
+        mp_obj_list_append(dir_list, mp_obj_subscr(next, MP_OBJ_NEW_SMALL_INT(0), MP_OBJ_SENTINEL));
     }
     return dir_list;
 }
diff --git a/ports/stm32f4/boards/feather_stm32f405_express/pins.c b/ports/stm32f4/boards/feather_stm32f405_express/pins.c
index 180fdd0937..ebc8fa337e 100644
--- a/ports/stm32f4/boards/feather_stm32f405_express/pins.c
+++ b/ports/stm32f4/boards/feather_stm32f405_express/pins.c
@@ -7,6 +7,7 @@ STATIC const mp_rom_map_elem_t board_module_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR_A3), MP_ROM_PTR(&pin_PA07) },
     { MP_ROM_QSTR(MP_QSTR_A4), MP_ROM_PTR(&pin_PC04) },
     { MP_ROM_QSTR(MP_QSTR_A5), MP_ROM_PTR(&pin_PC05) },
+    { MP_ROM_QSTR(MP_QSTR_VOLTAGE_MONITOR), MP_ROM_PTR(&pin_PA03) },
 
     { MP_ROM_QSTR(MP_QSTR_D5), MP_ROM_PTR(&pin_PC07) },
     { MP_ROM_QSTR(MP_QSTR_D6), MP_ROM_PTR(&pin_PC06) },
diff --git a/ports/stm32f4/boards/stm32f411ce_blackpill/mpconfigboard.h b/ports/stm32f4/boards/stm32f411ce_blackpill/mpconfigboard.h
index a438b5baa6..05e2a384a1 100644
--- a/ports/stm32f4/boards/stm32f411ce_blackpill/mpconfigboard.h
+++ b/ports/stm32f4/boards/stm32f411ce_blackpill/mpconfigboard.h
@@ -33,6 +33,7 @@
 #define FLASH_PAGE_SIZE             (0x4000)
 
 #define BOARD_OSC_DIV 25
+#define BOARD_NO_VBUS_SENSE
 
 // On-board flash
 // #define SPI_FLASH_MOSI_PIN          (&pin_PA07)
diff --git a/ports/stm32f4/supervisor/usb.c b/ports/stm32f4/supervisor/usb.c
index f327050f58..0d2d5cce9d 100644
--- a/ports/stm32f4/supervisor/usb.c
+++ b/ports/stm32f4/supervisor/usb.c
@@ -32,8 +32,33 @@
 #include "lib/mp-readline/readline.h"
 #include "stm32f4xx_hal.h"
 
+#include "py/mpconfig.h"
+
 #include "common-hal/microcontroller/Pin.h"
 
+STATIC void init_usb_vbus_sense(void) {
+
+#ifdef BOARD_NO_VBUS_SENSE
+    // Disable VBUS sensing
+    #ifdef USB_OTG_GCCFG_VBDEN
+        USB_OTG_FS->GCCFG &= ~USB_OTG_GCCFG_VBDEN;
+    #else
+        USB_OTG_FS->GCCFG |= USB_OTG_GCCFG_NOVBUSSENS;
+        USB_OTG_FS->GCCFG &= ~USB_OTG_GCCFG_VBUSBSEN;
+        USB_OTG_FS->GCCFG &= ~USB_OTG_GCCFG_VBUSASEN;
+    #endif
+#else
+    // Enable VBUS hardware sensing
+    #ifdef USB_OTG_GCCFG_VBDEN
+        USB_OTG_FS->GCCFG |= USB_OTG_GCCFG_VBDEN;
+    #else
+        USB_OTG_FS->GCCFG &= ~USB_OTG_GCCFG_NOVBUSSENS;
+        USB_OTG_FS->GCCFG |= USB_OTG_GCCFG_VBUSBSEN; // B Device sense
+    #endif
+#endif
+}
+
+
 void init_usb_hardware(void) {
     //TODO: if future chips overload this with options, move to peripherals management. 
 
@@ -79,7 +104,9 @@ void init_usb_hardware(void) {
     HAL_GPIO_Init(GPIOG, &GPIO_InitStruct);
     never_reset_pin_number(0, 8);
 #endif
-
+    
     /* Peripheral clock enable */
     __HAL_RCC_USB_OTG_FS_CLK_ENABLE();
+
+    init_usb_vbus_sense();
 }
diff --git a/ports/unix/modjni.c b/ports/unix/modjni.c
index 8f0eac5a9d..e18a26f3c6 100644
--- a/ports/unix/modjni.c
+++ b/ports/unix/modjni.c
@@ -242,7 +242,7 @@ STATIC void get_jclass_name(jobject obj, char *buf) {
 }
 
 #pragma GCC diagnostic ignored "-Wunused-parameter"
-STATIC mp_obj_t jobject_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value, mp_obj_t instance) {
+STATIC mp_obj_t jobject_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
     mp_obj_jobject_t *self = self_in;
     mp_uint_t idx = mp_obj_get_int(index);
     char class_name[64];
@@ -311,7 +311,7 @@ STATIC mp_obj_t jobject_unary_op(mp_unary_op_t op, mp_obj_t self_in) {
 // TODO: subscr_load_adaptor & subscr_getiter convenience functions
 // should be moved to common location for reuse.
 STATIC mp_obj_t subscr_load_adaptor(mp_obj_t self_in, mp_obj_t index_in) {
-    return mp_obj_subscr(self_in, index_in, MP_OBJ_SENTINEL, self_in);
+    return mp_obj_subscr(self_in, index_in, MP_OBJ_SENTINEL);
 }
 MP_DEFINE_CONST_FUN_OBJ_2(subscr_load_adaptor_obj, subscr_load_adaptor);
 
diff --git a/py/obj.c b/py/obj.c
index 47aa1aebfc..09e71be4d6 100644
--- a/py/obj.c
+++ b/py/obj.c
@@ -487,11 +487,11 @@ mp_obj_t mp_obj_len_maybe(mp_obj_t o_in) {
     }
 }
 
-mp_obj_t mp_obj_subscr(mp_obj_t base, mp_obj_t index, mp_obj_t value, mp_obj_t instance) {
+mp_obj_t mp_obj_subscr(mp_obj_t base, mp_obj_t index, mp_obj_t value) {
     mp_obj_type_t *type = mp_obj_get_type(base);
 
     if (type->subscr != NULL) {
-        mp_obj_t ret = type->subscr(base, index, value, instance);
+        mp_obj_t ret = type->subscr(base, index, value);
         // May have called port specific C code. Make sure it didn't mess up the heap.
         assert_heap_ok();
         if (ret != MP_OBJ_NULL) {
@@ -546,7 +546,7 @@ STATIC mp_obj_t generic_it_iternext(mp_obj_t self_in) {
     mp_obj_type_t *type = mp_obj_get_type(self->obj);
     mp_obj_t current_length = type->unary_op(MP_UNARY_OP_LEN, self->obj);
     if (self->cur < MP_OBJ_SMALL_INT_VALUE(current_length)) {
-        mp_obj_t o_out = type->subscr(self->obj, MP_OBJ_NEW_SMALL_INT(self->cur), MP_OBJ_SENTINEL, self->obj);
+        mp_obj_t o_out = type->subscr(self->obj, MP_OBJ_NEW_SMALL_INT(self->cur), MP_OBJ_SENTINEL);
         self->cur += 1;
         return o_out;
     } else {
diff --git a/py/obj.h b/py/obj.h
index ff97b34d83..cf4216d02f 100644
--- a/py/obj.h
+++ b/py/obj.h
@@ -444,7 +444,7 @@ typedef mp_obj_t (*mp_call_fun_t)(mp_obj_t fun, size_t n_args, size_t n_kw, cons
 typedef mp_obj_t (*mp_unary_op_fun_t)(mp_unary_op_t op, mp_obj_t);
 typedef mp_obj_t (*mp_binary_op_fun_t)(mp_binary_op_t op, mp_obj_t, mp_obj_t);
 typedef void (*mp_attr_fun_t)(mp_obj_t self_in, qstr attr, mp_obj_t *dest);
-typedef mp_obj_t (*mp_subscr_fun_t)(mp_obj_t self_in, mp_obj_t index, mp_obj_t value, mp_obj_t instance);
+typedef mp_obj_t (*mp_subscr_fun_t)(mp_obj_t self_in, mp_obj_t index, mp_obj_t value);
 typedef mp_obj_t (*mp_getiter_fun_t)(mp_obj_t self_in, mp_obj_iter_buf_t *iter_buf);
 
 // Buffer protocol
@@ -707,7 +707,7 @@ size_t mp_get_index(const mp_obj_type_t *type, size_t len, mp_obj_t index, bool
 mp_obj_t mp_obj_id(mp_obj_t o_in);
 mp_obj_t mp_obj_len(mp_obj_t o_in);
 mp_obj_t mp_obj_len_maybe(mp_obj_t o_in); // may return MP_OBJ_NULL
-mp_obj_t mp_obj_subscr(mp_obj_t base, mp_obj_t index, mp_obj_t val, mp_obj_t instance);
+mp_obj_t mp_obj_subscr(mp_obj_t base, mp_obj_t index, mp_obj_t val);
 mp_obj_t mp_generic_unary_op(mp_unary_op_t op, mp_obj_t o_in);
 
 // cell
diff --git a/py/objarray.c b/py/objarray.c
index 6fffa84125..9114a63c5a 100644
--- a/py/objarray.c
+++ b/py/objarray.c
@@ -396,8 +396,7 @@ STATIC mp_obj_t array_extend(mp_obj_t self_in, mp_obj_t arg_in) {
 STATIC MP_DEFINE_CONST_FUN_OBJ_2(array_extend_obj, array_extend);
 #endif
 
-#pragma GCC diagnostic ignored "-Wunused-parameter"
-STATIC mp_obj_t array_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value, mp_obj_t instance) {
+STATIC mp_obj_t array_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value) {
     if (value == MP_OBJ_NULL) {
         // delete item
         // TODO implement
diff --git a/py/objdict.c b/py/objdict.c
index 2c07331e7c..5bbe939b1d 100644
--- a/py/objdict.c
+++ b/py/objdict.c
@@ -175,7 +175,7 @@ mp_obj_t mp_obj_dict_get(mp_obj_t self_in, mp_obj_t index) {
 }
 
 #pragma GCC diagnostic ignored "-Wunused-parameter"
-STATIC mp_obj_t dict_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value, mp_obj_t instance) {
+STATIC mp_obj_t dict_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
     if (value == MP_OBJ_NULL) {
         // delete
         mp_obj_dict_delete(self_in, index);
diff --git a/py/objlist.c b/py/objlist.c
index c544c27f05..64381bc706 100644
--- a/py/objlist.c
+++ b/py/objlist.c
@@ -159,12 +159,12 @@ STATIC mp_obj_t list_binary_op(mp_binary_op_t op, mp_obj_t lhs, mp_obj_t rhs) {
 }
 
 #pragma GCC diagnostic ignored "-Wunused-parameter"
-STATIC mp_obj_t list_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value, mp_obj_t instance) {
+STATIC mp_obj_t list_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
+    mp_obj_list_t *self = mp_instance_cast_to_native_base(self_in, &mp_type_list);
     if (value == MP_OBJ_NULL) {
         // delete
 #if MICROPY_PY_BUILTINS_SLICE
         if (MP_OBJ_IS_TYPE(index, &mp_type_slice)) {
-            mp_obj_list_t *self = MP_OBJ_TO_PTR(self_in);
             mp_bound_slice_t slice;
             if (!mp_seq_get_fast_slice_indexes(self->len, index, &slice)) {
                 mp_raise_NotImplementedError(NULL);
@@ -180,12 +180,11 @@ STATIC mp_obj_t list_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value, mp
             return mp_const_none;
         }
 #endif
-        mp_obj_t args[2] = {self_in, index};
+        mp_obj_t args[2] = {self, index};
         list_pop(2, args);
         return mp_const_none;
     } else if (value == MP_OBJ_SENTINEL) {
         // load
-        mp_obj_list_t *self = MP_OBJ_TO_PTR(self_in);
 #if MICROPY_PY_BUILTINS_SLICE
         if (MP_OBJ_IS_TYPE(index, &mp_type_slice)) {
             mp_bound_slice_t slice;
@@ -202,7 +201,6 @@ STATIC mp_obj_t list_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value, mp
     } else {
 #if MICROPY_PY_BUILTINS_SLICE
         if (MP_OBJ_IS_TYPE(index, &mp_type_slice)) {
-            mp_obj_list_t *self = MP_OBJ_TO_PTR(self_in);
             size_t value_len; mp_obj_t *value_items;
             mp_obj_get_array(value, &value_len, &value_items);
             mp_bound_slice_t slice_out;
@@ -231,7 +229,7 @@ STATIC mp_obj_t list_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value, mp
             return mp_const_none;
         }
 #endif
-        mp_obj_list_store(self_in, index, value);
+        mp_obj_list_store(self, index, value);
         return mp_const_none;
     }
 }
diff --git a/py/objnamedtuple.c b/py/objnamedtuple.c
index a044fe3ff8..a0a64f9b25 100644
--- a/py/objnamedtuple.c
+++ b/py/objnamedtuple.c
@@ -31,6 +31,7 @@
 #include "py/runtime.h"
 #include "py/objstr.h"
 #include "py/objnamedtuple.h"
+#include "py/objtype.h"
 
 #include "supervisor/shared/translate.h"
 
@@ -70,6 +71,15 @@ void namedtuple_print(const mp_print_t *print, mp_obj_t o_in, mp_print_kind_t ki
     mp_obj_attrtuple_print_helper(print, fields, &o->tuple);
 }
 
+mp_obj_t namedtuple_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
+    mp_obj_type_t *type = mp_obj_get_type(self_in);
+    // Check for subclasses of namedtuple and unpack if needed.
+    if (type->parent != &mp_type_tuple) {
+        self_in = ((mp_obj_instance_t*) self_in)->subobj[0];
+    }
+    return mp_obj_tuple_subscr(self_in, index, value);
+}
+
 void namedtuple_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
     if (dest[0] == MP_OBJ_NULL) {
         // load attribute
@@ -167,7 +177,7 @@ STATIC mp_obj_t mp_obj_new_namedtuple_type(qstr name, size_t n_fields, mp_obj_t
     o->base.unary_op = mp_obj_tuple_unary_op;
     o->base.binary_op = mp_obj_tuple_binary_op;
     o->base.attr = namedtuple_attr;
-    o->base.subscr = mp_obj_tuple_subscr;
+    o->base.subscr = namedtuple_subscr;
     o->base.getiter = mp_obj_tuple_getiter;
     o->base.parent = &mp_type_tuple;
     return MP_OBJ_FROM_PTR(o);
diff --git a/py/objnamedtuple.h b/py/objnamedtuple.h
index 0ea0d28622..5a7512e3a6 100644
--- a/py/objnamedtuple.h
+++ b/py/objnamedtuple.h
@@ -49,6 +49,7 @@ typedef struct _mp_obj_namedtuple_t {
 
 void namedtuple_print(const mp_print_t *print, mp_obj_t o_in, mp_print_kind_t kind);
 size_t mp_obj_namedtuple_find_field(const mp_obj_namedtuple_type_t *type, qstr name);
+mp_obj_t namedtuple_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value);
 void namedtuple_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest);
 mp_obj_namedtuple_type_t *mp_obj_new_namedtuple_base(size_t n_fields, mp_obj_t *fields);
 mp_obj_t namedtuple_make_new(const mp_obj_type_t *type_in, size_t n_args, const mp_obj_t *args, mp_map_t *kw_args);
diff --git a/py/objrange.c b/py/objrange.c
index 328416303d..6f14bcc9f9 100644
--- a/py/objrange.c
+++ b/py/objrange.c
@@ -159,7 +159,7 @@ STATIC mp_obj_t range_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs
 #endif
 
 #pragma GCC diagnostic ignored "-Wunused-parameter"
-STATIC mp_obj_t range_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value, mp_obj_t instance) {
+STATIC mp_obj_t range_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
     if (value == MP_OBJ_SENTINEL) {
         // load
         mp_obj_range_t *self = MP_OBJ_TO_PTR(self_in);
diff --git a/py/objreversed.c b/py/objreversed.c
index 0b21e69380..4937d08189 100644
--- a/py/objreversed.c
+++ b/py/objreversed.c
@@ -66,7 +66,7 @@ STATIC mp_obj_t reversed_iternext(mp_obj_t self_in) {
 
     // pre-decrement and index sequence
     self->cur_index -= 1;
-    return mp_obj_subscr(self->seq, MP_OBJ_NEW_SMALL_INT(self->cur_index), MP_OBJ_SENTINEL, self->seq);
+    return mp_obj_subscr(self->seq, MP_OBJ_NEW_SMALL_INT(self->cur_index), MP_OBJ_SENTINEL);
 }
 
 const mp_obj_type_t mp_type_reversed = {
diff --git a/py/objstr.c b/py/objstr.c
index fd802fe852..567e734442 100644
--- a/py/objstr.c
+++ b/py/objstr.c
@@ -440,7 +440,7 @@ const byte *str_index_to_ptr(const mp_obj_type_t *type, const byte *self_data, s
 
 // This is used for both bytes and 8-bit strings. This is not used for unicode strings.
 #pragma GCC diagnostic ignored "-Wunused-parameter"
-STATIC mp_obj_t bytes_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value, mp_obj_t instance) {
+STATIC mp_obj_t bytes_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
     mp_obj_type_t *type = mp_obj_get_type(self_in);
     GET_STR_DATA_LEN(self_in, self_data, self_len);
     if (value == MP_OBJ_SENTINEL) {
diff --git a/py/objstrunicode.c b/py/objstrunicode.c
index dc8c0743d3..2540a1d7b6 100644
--- a/py/objstrunicode.c
+++ b/py/objstrunicode.c
@@ -198,7 +198,7 @@ const byte *str_index_to_ptr(const mp_obj_type_t *type, const byte *self_data, s
 }
 
 #pragma GCC diagnostic ignored "-Wunused-parameter"
-STATIC mp_obj_t str_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value, mp_obj_t instance) {
+STATIC mp_obj_t str_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
     mp_obj_type_t *type = mp_obj_get_type(self_in);
     assert(type == &mp_type_str);
     GET_STR_DATA_LEN(self_in, self_data, self_len);
diff --git a/py/objtuple.c b/py/objtuple.c
index b6640def51..b7f50d3b2c 100644
--- a/py/objtuple.c
+++ b/py/objtuple.c
@@ -178,7 +178,8 @@ mp_obj_t mp_obj_tuple_binary_op(mp_binary_op_t op, mp_obj_t lhs, mp_obj_t rhs) {
 }
 
 #pragma GCC diagnostic ignored "-Wunused-parameter"
-mp_obj_t mp_obj_tuple_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value, mp_obj_t instance) {
+mp_obj_t mp_obj_tuple_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
+
     if (value == MP_OBJ_SENTINEL) {
         // load
         mp_obj_tuple_t *self = MP_OBJ_TO_PTR(self_in);
diff --git a/py/objtuple.h b/py/objtuple.h
index 4df3aeded9..7f20ab7b6f 100644
--- a/py/objtuple.h
+++ b/py/objtuple.h
@@ -45,7 +45,7 @@ extern const mp_obj_type_t mp_type_tuple;
 void mp_obj_tuple_print(const mp_print_t *print, mp_obj_t o_in, mp_print_kind_t kind);
 mp_obj_t mp_obj_tuple_unary_op(mp_unary_op_t op, mp_obj_t self_in);
 mp_obj_t mp_obj_tuple_binary_op(mp_binary_op_t op, mp_obj_t lhs, mp_obj_t rhs);
-mp_obj_t mp_obj_tuple_subscr(mp_obj_t base, mp_obj_t index, mp_obj_t value, mp_obj_t instance);
+mp_obj_t mp_obj_tuple_subscr(mp_obj_t base, mp_obj_t index, mp_obj_t value);
 mp_obj_t mp_obj_tuple_getiter(mp_obj_t o_in, mp_obj_iter_buf_t *iter_buf);
 
 extern const mp_obj_type_t mp_type_attrtuple;
diff --git a/py/objtype.c b/py/objtype.c
index 9608a9242d..a5e733208c 100644
--- a/py/objtype.c
+++ b/py/objtype.c
@@ -34,6 +34,7 @@
 #include "py/objtype.h"
 #include "py/runtime.h"
 
+#include "supervisor/shared/stack.h"
 #include "supervisor/shared/translate.h"
 
 #if MICROPY_DEBUG_VERBOSE // print debugging info
@@ -825,7 +826,7 @@ STATIC void mp_obj_instance_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
     }
 }
 
-STATIC mp_obj_t instance_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value, mp_obj_t instance) {
+STATIC mp_obj_t instance_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
     mp_obj_instance_t *self = MP_OBJ_TO_PTR(self_in);
     mp_obj_t member[2] = {MP_OBJ_NULL};
     struct class_lookup_data lookup = {
@@ -851,8 +852,13 @@ STATIC mp_obj_t instance_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value
         mp_obj_class_lookup(&lookup, self->base.type);
         meth_args = 3;
     }
-    if (member[0] == MP_OBJ_SENTINEL) {
-        return mp_obj_subscr(self->subobj[0], index, value, instance);
+    if (member[0] == MP_OBJ_SENTINEL) { // native base subscr exists
+        mp_obj_type_t *subobj_type = mp_obj_get_type(self->subobj[0]);
+        // return mp_obj_subscr(self->subobj[0], index, value, instance);
+        mp_obj_t ret = subobj_type->subscr(self_in, index, value);
+        // May have called port specific C code. Make sure it didn't mess up the heap.
+        assert_heap_ok();
+        return ret;
     } else if (member[0] != MP_OBJ_NULL) {
         mp_obj_t args[3] = {self_in, index, value};
         // TODO probably need to call mp_convert_member_lookup, and use mp_call_method_n_kw
diff --git a/py/opmethods.c b/py/opmethods.c
index d906ddb6a3..247fa5bbc8 100644
--- a/py/opmethods.c
+++ b/py/opmethods.c
@@ -29,19 +29,19 @@
 
 STATIC mp_obj_t op_getitem(mp_obj_t self_in, mp_obj_t key_in) {
     mp_obj_type_t *type = mp_obj_get_type(self_in);
-    return type->subscr(self_in, key_in, MP_OBJ_SENTINEL, self_in);
+    return type->subscr(self_in, key_in, MP_OBJ_SENTINEL);
 }
 MP_DEFINE_CONST_FUN_OBJ_2(mp_op_getitem_obj, op_getitem);
 
 STATIC mp_obj_t op_setitem(mp_obj_t self_in, mp_obj_t key_in, mp_obj_t value_in) {
     mp_obj_type_t *type = mp_obj_get_type(self_in);
-    return type->subscr(self_in, key_in, value_in, self_in);
+    return type->subscr(self_in, key_in, value_in);
 }
 MP_DEFINE_CONST_FUN_OBJ_3(mp_op_setitem_obj, op_setitem);
 
 STATIC mp_obj_t op_delitem(mp_obj_t self_in, mp_obj_t key_in) {
     mp_obj_type_t *type = mp_obj_get_type(self_in);
-    return type->subscr(self_in, key_in, MP_OBJ_NULL, self_in);
+    return type->subscr(self_in, key_in, MP_OBJ_NULL);
 }
 MP_DEFINE_CONST_FUN_OBJ_2(mp_op_delitem_obj, op_delitem);
 
diff --git a/py/vm.c b/py/vm.c
index 2fe8d32370..353fc88100 100644
--- a/py/vm.c
+++ b/py/vm.c
@@ -386,7 +386,7 @@ dispatch_loop:
                 ENTRY(MP_BC_LOAD_SUBSCR): {
                     MARK_EXC_IP_SELECTIVE();
                     mp_obj_t index = POP();
-                    SET_TOP(mp_obj_subscr(TOP(), index, MP_OBJ_SENTINEL, TOP()));
+                    SET_TOP(mp_obj_subscr(TOP(), index, MP_OBJ_SENTINEL));
                     DISPATCH();
                 }
 
@@ -464,7 +464,7 @@ dispatch_loop:
 
                 ENTRY(MP_BC_STORE_SUBSCR):
                     MARK_EXC_IP_SELECTIVE();
-                    mp_obj_subscr(sp[-1], sp[0], sp[-2], sp[-1]);
+                    mp_obj_subscr(sp[-1], sp[0], sp[-2]);
                     sp -= 3;
                     DISPATCH();
 
diff --git a/shared-bindings/_pixelbuf/PixelBuf.c b/shared-bindings/_pixelbuf/PixelBuf.c
index 1ed6f7baf8..7c624a8fdf 100644
--- a/shared-bindings/_pixelbuf/PixelBuf.c
+++ b/shared-bindings/_pixelbuf/PixelBuf.c
@@ -368,7 +368,7 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_2(pixelbuf_pixelbuf_fill_obj, pixelbuf_pixelbuf_f
 //|
 //|     Sets the pixel value at the given index.
 //|
-STATIC mp_obj_t pixelbuf_pixelbuf_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value, mp_obj_t instance) {
+STATIC mp_obj_t pixelbuf_pixelbuf_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value) {
     if (value == MP_OBJ_NULL) {
         // delete item
         // slice deletion
@@ -431,7 +431,7 @@ STATIC mp_obj_t pixelbuf_pixelbuf_subscr(mp_obj_t self_in, mp_obj_t index_in, mp
                 }
             }
             if (self->auto_write)
-                call_show(instance);
+                call_show(self_in);
             return mp_const_none;
             #else
             return MP_OBJ_NULL; // op not supported
@@ -451,7 +451,7 @@ STATIC mp_obj_t pixelbuf_pixelbuf_subscr(mp_obj_t self_in, mp_obj_t index_in, mp
             pixelbuf_set_pixel(self->buf + offset, self->two_buffers ? self->rawbuf + offset : NULL,
                 self->brightness, value, &self->byteorder, self->byteorder.is_dotstar);
             if (self->auto_write)
-                call_show(instance);
+                call_show(self_in);
             return mp_const_none;
         }
     }
diff --git a/shared-bindings/displayio/Bitmap.c b/shared-bindings/displayio/Bitmap.c
index 7c77d05eda..ca9484a408 100644
--- a/shared-bindings/displayio/Bitmap.c
+++ b/shared-bindings/displayio/Bitmap.c
@@ -134,7 +134,7 @@ const mp_obj_property_t displayio_bitmap_height_obj = {
 //|       bitmap[0,1] = 3
 //|
 #pragma GCC diagnostic ignored "-Wunused-parameter"
-STATIC mp_obj_t bitmap_subscr(mp_obj_t self_in, mp_obj_t index_obj, mp_obj_t value_obj, mp_obj_t instance) {
+STATIC mp_obj_t bitmap_subscr(mp_obj_t self_in, mp_obj_t index_obj, mp_obj_t value_obj) {
     if (value_obj == mp_const_none) {
         // delete item
         mp_raise_AttributeError(translate("Cannot delete values"));
diff --git a/shared-bindings/displayio/Group.c b/shared-bindings/displayio/Group.c
index 40f2704c05..f5e3c22634 100644
--- a/shared-bindings/displayio/Group.c
+++ b/shared-bindings/displayio/Group.c
@@ -311,7 +311,7 @@ STATIC mp_obj_t group_unary_op(mp_unary_op_t op, mp_obj_t self_in) {
 //|       del group[0]
 //|
 #pragma GCC diagnostic ignored "-Wunused-parameter"
-STATIC mp_obj_t group_subscr(mp_obj_t self_in, mp_obj_t index_obj, mp_obj_t value, mp_obj_t instance) {
+STATIC mp_obj_t group_subscr(mp_obj_t self_in, mp_obj_t index_obj, mp_obj_t value) {
     displayio_group_t *self = native_group(self_in);
 
     if (MP_OBJ_IS_TYPE(index_obj, &mp_type_slice)) {
diff --git a/shared-bindings/displayio/Palette.c b/shared-bindings/displayio/Palette.c
index 2fa65867aa..903338abb2 100644
--- a/shared-bindings/displayio/Palette.c
+++ b/shared-bindings/displayio/Palette.c
@@ -96,7 +96,7 @@ STATIC mp_obj_t group_unary_op(mp_unary_op_t op, mp_obj_t self_in) {
 //|       palette[3] = bytearray(b'\x00\x00\xFF')   # set using a bytearay of 3 or 4 bytes
 //|
 #pragma GCC diagnostic ignored "-Wunused-parameter"
-STATIC mp_obj_t palette_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value, mp_obj_t instance) {
+STATIC mp_obj_t palette_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value) {
     if (value == MP_OBJ_NULL) {
         // delete item
         return MP_OBJ_NULL; // op not supported
diff --git a/shared-bindings/displayio/TileGrid.c b/shared-bindings/displayio/TileGrid.c
index 5acf8496f8..288eb4b236 100644
--- a/shared-bindings/displayio/TileGrid.c
+++ b/shared-bindings/displayio/TileGrid.c
@@ -349,7 +349,7 @@ const mp_obj_property_t displayio_tilegrid_pixel_shader_obj = {
 //|
 //|       grid[0,0] = 10
 //|
-STATIC mp_obj_t tilegrid_subscr(mp_obj_t self_in, mp_obj_t index_obj, mp_obj_t value_obj, mp_obj_t instance) {
+STATIC mp_obj_t tilegrid_subscr(mp_obj_t self_in, mp_obj_t index_obj, mp_obj_t value_obj) {
     displayio_tilegrid_t *self = native_tilegrid(self_in);
 
 
diff --git a/shared-bindings/nvm/ByteArray.c b/shared-bindings/nvm/ByteArray.c
index 5ac46b260c..31bedeacc0 100644
--- a/shared-bindings/nvm/ByteArray.c
+++ b/shared-bindings/nvm/ByteArray.c
@@ -70,7 +70,7 @@ STATIC const mp_rom_map_elem_t nvm_bytearray_locals_dict_table[] = {
 
 STATIC MP_DEFINE_CONST_DICT(nvm_bytearray_locals_dict, nvm_bytearray_locals_dict_table);
 
-STATIC mp_obj_t nvm_bytearray_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value, mp_obj_t instance) {
+STATIC mp_obj_t nvm_bytearray_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value) {
     if (value == MP_OBJ_NULL) {
         // delete item
         // slice deletion
diff --git a/shared-bindings/pulseio/PulseIn.c b/shared-bindings/pulseio/PulseIn.c
index 5947329a54..8b69109f04 100644
--- a/shared-bindings/pulseio/PulseIn.c
+++ b/shared-bindings/pulseio/PulseIn.c
@@ -272,7 +272,7 @@ STATIC mp_obj_t pulsein_unary_op(mp_unary_op_t op, mp_obj_t self_in) {
 //|       pulses = pulseio.PulseIn(pin)
 //|       print(pulses[0])
 //|
-STATIC mp_obj_t pulsein_subscr(mp_obj_t self_in, mp_obj_t index_obj, mp_obj_t value, mp_obj_t instance) {
+STATIC mp_obj_t pulsein_subscr(mp_obj_t self_in, mp_obj_t index_obj, mp_obj_t value) {
     if (value == mp_const_none) {
         // delete item
         mp_raise_AttributeError(translate("Cannot delete values"));
diff --git a/shared-bindings/random/__init__.c b/shared-bindings/random/__init__.c
index 110d59aa44..de4c90910d 100644
--- a/shared-bindings/random/__init__.c
+++ b/shared-bindings/random/__init__.c
@@ -145,7 +145,7 @@ STATIC mp_obj_t random_choice(mp_obj_t seq) {
     if (len == 0) {
         mp_raise_IndexError(translate("empty sequence"));
     }
-    return mp_obj_subscr(seq, mp_obj_new_int(shared_modules_random_randrange(0, len, 1)), MP_OBJ_SENTINEL, seq);
+    return mp_obj_subscr(seq, mp_obj_new_int(shared_modules_random_randrange(0, len, 1)), MP_OBJ_SENTINEL);
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(random_choice_obj, random_choice);
 
diff --git a/shared-module/os/__init__.c b/shared-module/os/__init__.c
index ad76251c81..8060eec4f3 100644
--- a/shared-module/os/__init__.c
+++ b/shared-module/os/__init__.c
@@ -127,7 +127,7 @@ mp_obj_t common_hal_os_listdir(const char* path) {
     mp_obj_t next;
     while ((next = mp_iternext(iter_obj)) != MP_OBJ_STOP_ITERATION) {
         // next[0] is the filename.
-        mp_obj_list_append(dir_list, mp_obj_subscr(next, MP_OBJ_NEW_SMALL_INT(0), MP_OBJ_SENTINEL, dir_list));
+        mp_obj_list_append(dir_list, mp_obj_subscr(next, MP_OBJ_NEW_SMALL_INT(0), MP_OBJ_SENTINEL));
         RUN_BACKGROUND_TASKS;
     }
     return dir_list;