diff --git a/.github/workflows/code_size.yml b/.github/workflows/code_size.yml
index a65a00201a..1ef43d1fd3 100644
--- a/.github/workflows/code_size.yml
+++ b/.github/workflows/code_size.yml
@@ -8,9 +8,15 @@ on:
       - 'tools/**'
       - 'py/**'
       - 'extmod/**'
+      - 'shared/**'
       - 'lib/**'
       - 'ports/bare-arm/**'
+      - 'ports/mimxrt/**'
       - 'ports/minimal/**'
+      - 'ports/rp2/**'
+      - 'ports/samd/**'
+      - 'ports/stm32/**'
+      - 'ports/unix/**'
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
diff --git a/.github/workflows/ports_unix.yml b/.github/workflows/ports_unix.yml
index 2367eddbe6..4473847db6 100644
--- a/.github/workflows/ports_unix.yml
+++ b/.github/workflows/ports_unix.yml
@@ -88,10 +88,11 @@ jobs:
         (cd ports/unix && gcov -o build-coverage/py ../../py/*.c || true)
         (cd ports/unix && gcov -o build-coverage/extmod ../../extmod/*.c || true)
     - name: Upload coverage to Codecov
-      uses: codecov/codecov-action@v3
+      uses: codecov/codecov-action@v4
       with:
         fail_ci_if_error: true
         verbose: true
+        token: ${{ secrets.CODECOV_TOKEN }}
     - name: Print failures
       if: failure()
       run: tests/run-tests.py --print-failures
diff --git a/extmod/modasyncio.c b/extmod/modasyncio.c
index 61dd707223..4f82370d23 100644
--- a/extmod/modasyncio.c
+++ b/extmod/modasyncio.c
@@ -156,7 +156,7 @@ static MP_DEFINE_CONST_OBJ_TYPE(
 // Task class
 
 // This is the core asyncio context with cur_task, _task_queue and CancelledError.
-static mp_obj_t asyncio_context = MP_OBJ_NULL;
+mp_obj_t mp_asyncio_context = MP_OBJ_NULL;
 
 static mp_obj_t task_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *args) {
     mp_arg_check_num(n_args, n_kw, 1, 2, false);
@@ -168,7 +168,7 @@ static mp_obj_t task_make_new(const mp_obj_type_t *type, size_t n_args, size_t n
     self->state = TASK_STATE_RUNNING_NOT_WAITED_ON;
     self->ph_key = MP_OBJ_NEW_SMALL_INT(0);
     if (n_args == 2) {
-        asyncio_context = args[1];
+        mp_asyncio_context = args[1];
     }
     return MP_OBJ_FROM_PTR(self);
 }
@@ -186,7 +186,7 @@ static mp_obj_t task_cancel(mp_obj_t self_in) {
         return mp_const_false;
     }
     // Can't cancel self (not supported yet).
-    mp_obj_t cur_task = mp_obj_dict_get(asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR_cur_task));
+    mp_obj_t cur_task = mp_obj_dict_get(mp_asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR_cur_task));
     if (self_in == cur_task) {
         mp_raise_msg(&mp_type_RuntimeError, MP_ERROR_TEXT("can't cancel self"));
     }
@@ -195,7 +195,7 @@ static mp_obj_t task_cancel(mp_obj_t self_in) {
         self = MP_OBJ_TO_PTR(self->data);
     }
 
-    mp_obj_t _task_queue = mp_obj_dict_get(asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR__task_queue));
+    mp_obj_t _task_queue = mp_obj_dict_get(mp_asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR__task_queue));
 
     // Reschedule Task as a cancelled task.
     mp_obj_t dest[3];
@@ -218,7 +218,7 @@ static mp_obj_t task_cancel(mp_obj_t self_in) {
         task_queue_push(2, dest);
     }
 
-    self->data = mp_obj_dict_get(asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR_CancelledError));
+    self->data = mp_obj_dict_get(mp_asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR_CancelledError));
 
     return mp_const_true;
 }
@@ -278,7 +278,7 @@ static mp_obj_t task_iternext(mp_obj_t self_in) {
         nlr_raise(self->data);
     } else {
         // Put calling task on waiting queue.
-        mp_obj_t cur_task = mp_obj_dict_get(asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR_cur_task));
+        mp_obj_t cur_task = mp_obj_dict_get(mp_asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR_cur_task));
         mp_obj_t args[2] = { self->state, cur_task };
         task_queue_push(2, args);
         // Set calling task's data to this task that it waits on, to double-link it.
diff --git a/ports/rp2/README.md b/ports/rp2/README.md
index e22fb3093d..c2f3771cd3 100644
--- a/ports/rp2/README.md
+++ b/ports/rp2/README.md
@@ -37,7 +37,7 @@ You can also build the standard CMake way.  The final firmware is found in
 the top-level of the CMake build directory (`build` by default) and is
 called `firmware.uf2`.
 
-If you are using a different board other than a Rasoberry Pi Pico, then you should
+If you are using a board other than a Raspberry Pi Pico, you should
 pass the board name to the build; e.g. for Raspberry Pi Pico W:
 
     $ make BOARD=RPI_PICO_W submodules
diff --git a/ports/rp2/modmachine.c b/ports/rp2/modmachine.c
index 6189e7dc53..5551bf723a 100644
--- a/ports/rp2/modmachine.c
+++ b/ports/rp2/modmachine.c
@@ -127,10 +127,10 @@ static void mp_machine_lightsleep(size_t n_args, const mp_obj_t *args) {
 
     const uint32_t xosc_hz = XOSC_MHZ * 1000000;
 
-    uint32_t my_interrupts = save_and_disable_interrupts();
+    uint32_t my_interrupts = mp_thread_begin_atomic_section();
     #if MICROPY_PY_NETWORK_CYW43
     if (cyw43_has_pending && cyw43_poll != NULL) {
-        restore_interrupts(my_interrupts);
+        mp_thread_end_atomic_section(my_interrupts);
         return;
     }
     #endif
@@ -165,8 +165,15 @@ static void mp_machine_lightsleep(size_t n_args, const mp_obj_t *args) {
     } else {
         uint32_t sleep_en0 = clocks_hw->sleep_en0;
         uint32_t sleep_en1 = clocks_hw->sleep_en1;
+        bool timer3_enabled = irq_is_enabled(3);
+
         clocks_hw->sleep_en0 = CLOCKS_SLEEP_EN0_CLK_RTC_RTC_BITS;
         if (use_timer_alarm) {
+            // Make sure ALARM3/IRQ3 is enabled on _this_ core
+            timer_hw->inte |= 1 << 3;
+            if (!timer3_enabled) {
+                irq_set_enabled(3, true);
+            }
             // Use timer alarm to wake.
             clocks_hw->sleep_en1 = CLOCKS_SLEEP_EN1_CLK_SYS_TIMER_BITS;
             timer_hw->alarm[3] = timer_hw->timerawl + delay_ms * 1000;
@@ -177,6 +184,9 @@ static void mp_machine_lightsleep(size_t n_args, const mp_obj_t *args) {
         scb_hw->scr |= M0PLUS_SCR_SLEEPDEEP_BITS;
         __wfi();
         scb_hw->scr &= ~M0PLUS_SCR_SLEEPDEEP_BITS;
+        if (!timer3_enabled) {
+            irq_set_enabled(3, false);
+        }
         clocks_hw->sleep_en0 = sleep_en0;
         clocks_hw->sleep_en1 = sleep_en1;
     }
@@ -186,7 +196,7 @@ static void mp_machine_lightsleep(size_t n_args, const mp_obj_t *args) {
 
     // Bring back all clocks.
     clocks_init();
-    restore_interrupts(my_interrupts);
+    mp_thread_end_atomic_section(my_interrupts);
 }
 
 NORETURN static void mp_machine_deepsleep(size_t n_args, const mp_obj_t *args) {
diff --git a/ports/webassembly/Makefile b/ports/webassembly/Makefile
index d0a8aa9924..93b92ef583 100644
--- a/ports/webassembly/Makefile
+++ b/ports/webassembly/Makefile
@@ -22,6 +22,9 @@ BUILD ?= build-$(VARIANT)
 include ../../py/mkenv.mk
 include $(VARIANT_DIR)/mpconfigvariant.mk
 
+# Use the default frozen manifest, variants may override this.
+FROZEN_MANIFEST ?= variants/manifest.py
+
 # Qstr definitions (must come before including py.mk).
 QSTR_DEFS = qstrdefsport.h
 
diff --git a/ports/webassembly/api.js b/ports/webassembly/api.js
index 7d1832af4f..2be82e8907 100644
--- a/ports/webassembly/api.js
+++ b/ports/webassembly/api.js
@@ -38,7 +38,7 @@ export async function loadMicroPython(options) {
         { heapsize: 1024 * 1024, linebuffer: true },
         options,
     );
-    const Module = {};
+    let Module = {};
     Module.locateFile = (path, scriptDirectory) =>
         url || scriptDirectory + path;
     Module._textDecoder = new TextDecoder();
@@ -83,11 +83,7 @@ export async function loadMicroPython(options) {
             Module.stderr = (c) => stderr(new Uint8Array([c]));
         }
     }
-    const moduleLoaded = new Promise((r) => {
-        Module.postRun = r;
-    });
-    _createMicroPythonModule(Module);
-    await moduleLoaded;
+    Module = await _createMicroPythonModule(Module);
     globalThis.Module = Module;
     proxy_js_init();
     const pyimport = (name) => {
@@ -131,23 +127,31 @@ export async function loadMicroPython(options) {
         },
         pyimport: pyimport,
         runPython(code) {
+            const len = Module.lengthBytesUTF8(code);
+            const buf = Module._malloc(len + 1);
+            Module.stringToUTF8(code, buf, len + 1);
             const value = Module._malloc(3 * 4);
             Module.ccall(
                 "mp_js_do_exec",
                 "number",
-                ["string", "pointer"],
-                [code, value],
+                ["pointer", "number", "pointer"],
+                [buf, len, value],
             );
+            Module._free(buf);
             return proxy_convert_mp_to_js_obj_jsside_with_free(value);
         },
         runPythonAsync(code) {
+            const len = Module.lengthBytesUTF8(code);
+            const buf = Module._malloc(len + 1);
+            Module.stringToUTF8(code, buf, len + 1);
             const value = Module._malloc(3 * 4);
             Module.ccall(
                 "mp_js_do_exec_async",
                 "number",
-                ["string", "pointer"],
-                [code, value],
+                ["pointer", "number", "pointer"],
+                [buf, len, value],
             );
+            Module._free(buf);
             return proxy_convert_mp_to_js_obj_jsside_with_free(value);
         },
         replInit() {
@@ -224,6 +228,16 @@ async function runCLI() {
             }
         });
     } else {
+        // If the script to run ends with a running of the asyncio main loop, then inject
+        // a simple `asyncio.run` hook that starts the main task.  This is primarily to
+        // support running the standard asyncio tests.
+        if (contents.endsWith("asyncio.run(main())\n")) {
+            const asyncio = mp.pyimport("asyncio");
+            asyncio.run = async (task) => {
+                await asyncio.create_task(task);
+            };
+        }
+
         try {
             mp.runPython(contents);
         } catch (error) {
diff --git a/ports/webassembly/asyncio/__init__.py b/ports/webassembly/asyncio/__init__.py
new file mode 100644
index 0000000000..ba1ca63514
--- /dev/null
+++ b/ports/webassembly/asyncio/__init__.py
@@ -0,0 +1,9 @@
+# MicroPython asyncio module, for use with webassembly port
+# MIT license; Copyright (c) 2024 Damien P. George
+
+from .core import *
+from .funcs import wait_for, wait_for_ms, gather
+from .event import Event
+from .lock import Lock
+
+__version__ = (3, 0, 0)
diff --git a/ports/webassembly/asyncio/core.py b/ports/webassembly/asyncio/core.py
new file mode 100644
index 0000000000..a128bb6055
--- /dev/null
+++ b/ports/webassembly/asyncio/core.py
@@ -0,0 +1,249 @@
+# MicroPython asyncio module, for use with webassembly port
+# MIT license; Copyright (c) 2019-2024 Damien P. George
+
+from time import ticks_ms as ticks, ticks_diff, ticks_add
+import sys, js, jsffi
+
+# Import TaskQueue and Task from built-in C code.
+from _asyncio import TaskQueue, Task
+
+
+################################################################################
+# Exceptions
+
+
+class CancelledError(BaseException):
+    pass
+
+
+class TimeoutError(Exception):
+    pass
+
+
+# Used when calling Loop.call_exception_handler.
+_exc_context = {"message": "Task exception wasn't retrieved", "exception": None, "future": None}
+
+
+################################################################################
+# Sleep functions
+
+
+# "Yield" once, then raise StopIteration
+class SingletonGenerator:
+    def __init__(self):
+        self.state = None
+        self.exc = StopIteration()
+
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        if self.state is not None:
+            _task_queue.push(cur_task, self.state)
+            self.state = None
+            return None
+        else:
+            self.exc.__traceback__ = None
+            raise self.exc
+
+
+# Pause task execution for the given time (integer in milliseconds, uPy extension)
+# Use a SingletonGenerator to do it without allocating on the heap
+def sleep_ms(t, sgen=SingletonGenerator()):
+    if cur_task is None:
+        # Support top-level asyncio.sleep, via a JavaScript Promise.
+        return jsffi.async_timeout_ms(t)
+    assert sgen.state is None
+    sgen.state = ticks_add(ticks(), max(0, t))
+    return sgen
+
+
+# Pause task execution for the given time (in seconds)
+def sleep(t):
+    return sleep_ms(int(t * 1000))
+
+
+################################################################################
+# Main run loop
+
+asyncio_timer = None
+
+
+class ThenableEvent:
+    def __init__(self, thenable):
+        self.result = None  # Result of the thenable
+        self.waiting = None  # Task waiting on completion of this thenable
+        thenable.then(self.set)
+
+    def set(self, value):
+        # Thenable/Promise is fulfilled, set result and schedule any waiting task.
+        self.result = value
+        if self.waiting:
+            _task_queue.push(self.waiting)
+            self.waiting = None
+            _schedule_run_iter(0)
+
+    def remove(self, task):
+        self.waiting = None
+
+    # async
+    def wait(self):
+        # Set the calling task as the task waiting on this thenable.
+        self.waiting = cur_task
+        # Set calling task's data to this object so it can be removed if needed.
+        cur_task.data = self
+        # Wait for the thenable to fulfill.
+        yield
+        # Return the result of the thenable.
+        return self.result
+
+
+# Ensure the awaitable is a task
+def _promote_to_task(aw):
+    return aw if isinstance(aw, Task) else create_task(aw)
+
+
+def _schedule_run_iter(dt):
+    global asyncio_timer
+    if asyncio_timer is not None:
+        js.clearTimeout(asyncio_timer)
+    asyncio_timer = js.setTimeout(_run_iter, dt)
+
+
+def _run_iter():
+    global cur_task
+    excs_all = (CancelledError, Exception)  # To prevent heap allocation in loop
+    excs_stop = (CancelledError, StopIteration)  # To prevent heap allocation in loop
+    while True:
+        # Wait until the head of _task_queue is ready to run
+        t = _task_queue.peek()
+        if t:
+            # A task waiting on _task_queue; "ph_key" is time to schedule task at
+            dt = max(0, ticks_diff(t.ph_key, ticks()))
+        else:
+            # No tasks can be woken so finished running
+            cur_task = None
+            return
+
+        if dt > 0:
+            # schedule to call again later
+            cur_task = None
+            _schedule_run_iter(dt)
+            return
+
+        # Get next task to run and continue it
+        t = _task_queue.pop()
+        cur_task = t
+        try:
+            # Continue running the coroutine, it's responsible for rescheduling itself
+            exc = t.data
+            if not exc:
+                t.coro.send(None)
+            else:
+                # If the task is finished and on the run queue and gets here, then it
+                # had an exception and was not await'ed on.  Throwing into it now will
+                # raise StopIteration and the code below will catch this and run the
+                # call_exception_handler function.
+                t.data = None
+                t.coro.throw(exc)
+        except excs_all as er:
+            # Check the task is not on any event queue
+            assert t.data is None
+            # This task is done.
+            if t.state:
+                # Task was running but is now finished.
+                waiting = False
+                if t.state is True:
+                    # "None" indicates that the task is complete and not await'ed on (yet).
+                    t.state = None
+                elif callable(t.state):
+                    # The task has a callback registered to be called on completion.
+                    t.state(t, er)
+                    t.state = False
+                    waiting = True
+                else:
+                    # Schedule any other tasks waiting on the completion of this task.
+                    while t.state.peek():
+                        _task_queue.push(t.state.pop())
+                        waiting = True
+                    # "False" indicates that the task is complete and has been await'ed on.
+                    t.state = False
+                if not waiting and not isinstance(er, excs_stop):
+                    # An exception ended this detached task, so queue it for later
+                    # execution to handle the uncaught exception if no other task retrieves
+                    # the exception in the meantime (this is handled by Task.throw).
+                    _task_queue.push(t)
+                # Save return value of coro to pass up to caller.
+                t.data = er
+            elif t.state is None:
+                # Task is already finished and nothing await'ed on the task,
+                # so call the exception handler.
+
+                # Save exception raised by the coro for later use.
+                t.data = exc
+
+                # Create exception context and call the exception handler.
+                _exc_context["exception"] = exc
+                _exc_context["future"] = t
+                Loop.call_exception_handler(_exc_context)
+
+
+# Create and schedule a new task from a coroutine.
+def create_task(coro):
+    if not hasattr(coro, "send"):
+        raise TypeError("coroutine expected")
+    t = Task(coro, globals())
+    _task_queue.push(t)
+    _schedule_run_iter(0)
+    return t
+
+
+################################################################################
+# Event loop wrapper
+
+
+cur_task = None
+
+
+class Loop:
+    _exc_handler = None
+
+    def create_task(coro):
+        return create_task(coro)
+
+    def close():
+        pass
+
+    def set_exception_handler(handler):
+        Loop._exc_handler = handler
+
+    def get_exception_handler():
+        return Loop._exc_handler
+
+    def default_exception_handler(loop, context):
+        print(context["message"], file=sys.stderr)
+        print("future:", context["future"], "coro=", context["future"].coro, file=sys.stderr)
+        sys.print_exception(context["exception"], sys.stderr)
+
+    def call_exception_handler(context):
+        (Loop._exc_handler or Loop.default_exception_handler)(Loop, context)
+
+
+def get_event_loop():
+    return Loop
+
+
+def current_task():
+    if cur_task is None:
+        raise RuntimeError("no running event loop")
+    return cur_task
+
+
+def new_event_loop():
+    global _task_queue
+    _task_queue = TaskQueue()  # TaskQueue of Task instances.
+    return Loop
+
+
+# Initialise default event loop.
+new_event_loop()
diff --git a/ports/webassembly/main.c b/ports/webassembly/main.c
index 441c6d67e3..23d12b6dbb 100644
--- a/ports/webassembly/main.c
+++ b/ports/webassembly/main.c
@@ -104,7 +104,7 @@ void mp_js_do_import(const char *name, uint32_t *out) {
     }
 }
 
-void mp_js_do_exec(const char *src, uint32_t *out) {
+void mp_js_do_exec(const char *src, size_t len, uint32_t *out) {
     // Collect at the top-level, where there are no root pointers from stack/registers.
     gc_collect_start();
     gc_collect_end();
@@ -112,7 +112,7 @@ void mp_js_do_exec(const char *src, uint32_t *out) {
     mp_parse_input_kind_t input_kind = MP_PARSE_FILE_INPUT;
     nlr_buf_t nlr;
     if (nlr_push(&nlr) == 0) {
-        mp_lexer_t *lex = mp_lexer_new_from_str_len_dedent(MP_QSTR__lt_stdin_gt_, src, strlen(src), 0);
+        mp_lexer_t *lex = mp_lexer_new_from_str_len_dedent(MP_QSTR__lt_stdin_gt_, src, len, 0);
         qstr source_name = lex->source_name;
         mp_parse_tree_t parse_tree = mp_parse(lex, input_kind);
         mp_obj_t module_fun = mp_compile(&parse_tree, source_name, false);
@@ -125,9 +125,9 @@ void mp_js_do_exec(const char *src, uint32_t *out) {
     }
 }
 
-void mp_js_do_exec_async(const char *src, uint32_t *out) {
+void mp_js_do_exec_async(const char *src, size_t len, uint32_t *out) {
     mp_compile_allow_top_level_await = true;
-    mp_js_do_exec(src, out);
+    mp_js_do_exec(src, len, out);
     mp_compile_allow_top_level_await = false;
 }
 
diff --git a/ports/webassembly/modjsffi.c b/ports/webassembly/modjsffi.c
index d4e61e368f..cb2f578f8f 100644
--- a/ports/webassembly/modjsffi.c
+++ b/ports/webassembly/modjsffi.c
@@ -61,12 +61,27 @@ static mp_obj_t mp_jsffi_to_js(mp_obj_t arg) {
 }
 static MP_DEFINE_CONST_FUN_OBJ_1(mp_jsffi_to_js_obj, mp_jsffi_to_js);
 
+// *FORMAT-OFF*
+EM_JS(void, promise_with_timeout_ms, (double ms, uint32_t * out), {
+    const ret = new Promise((resolve) => setTimeout(resolve, ms));
+    proxy_convert_js_to_mp_obj_jsside(ret, out);
+});
+// *FORMAT-ON*
+
+static mp_obj_t mp_jsffi_async_timeout_ms(mp_obj_t arg) {
+    uint32_t out[PVN];
+    promise_with_timeout_ms(mp_obj_get_float_to_d(arg), out);
+    return proxy_convert_js_to_mp_obj_cside(out);
+}
+static MP_DEFINE_CONST_FUN_OBJ_1(mp_jsffi_async_timeout_ms_obj, mp_jsffi_async_timeout_ms);
+
 static const mp_rom_map_elem_t mp_module_jsffi_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_jsffi) },
 
     { MP_ROM_QSTR(MP_QSTR_JsProxy), MP_ROM_PTR(&mp_type_jsproxy) },
     { MP_ROM_QSTR(MP_QSTR_create_proxy), MP_ROM_PTR(&mp_jsffi_create_proxy_obj) },
     { MP_ROM_QSTR(MP_QSTR_to_js), MP_ROM_PTR(&mp_jsffi_to_js_obj) },
+    { MP_ROM_QSTR(MP_QSTR_async_timeout_ms), MP_ROM_PTR(&mp_jsffi_async_timeout_ms_obj) },
 };
 static MP_DEFINE_CONST_DICT(mp_module_jsffi_globals, mp_module_jsffi_globals_table);
 
diff --git a/ports/webassembly/objjsproxy.c b/ports/webassembly/objjsproxy.c
index 098f4e75f5..15fbb57523 100644
--- a/ports/webassembly/objjsproxy.c
+++ b/ports/webassembly/objjsproxy.c
@@ -346,6 +346,12 @@ typedef struct _jsproxy_gen_t {
 
 mp_vm_return_kind_t jsproxy_gen_resume(mp_obj_t self_in, mp_obj_t send_value, mp_obj_t throw_value, mp_obj_t *ret_val) {
     jsproxy_gen_t *self = MP_OBJ_TO_PTR(self_in);
+
+    if (throw_value) {
+        *ret_val = throw_value;
+        return MP_VM_RETURN_EXCEPTION;
+    }
+
     switch (self->state) {
         case JSOBJ_GEN_STATE_WAITING:
             self->state = JSOBJ_GEN_STATE_COMPLETED;
@@ -468,9 +474,29 @@ static mp_obj_t jsproxy_new_gen(mp_obj_t self_in, mp_obj_iter_buf_t *iter_buf) {
 
 /******************************************************************************/
 
+#if MICROPY_PY_ASYNCIO
+extern mp_obj_t mp_asyncio_context;
+#endif
+
 static mp_obj_t jsproxy_getiter(mp_obj_t self_in, mp_obj_iter_buf_t *iter_buf) {
     mp_obj_jsproxy_t *self = MP_OBJ_TO_PTR(self_in);
     if (has_attr(self->ref, "then")) {
+        #if MICROPY_PY_ASYNCIO
+        // When asyncio is running and the caller here is a task, wrap the JavaScript
+        // thenable in a ThenableEvent, and get the task to wait on that event.  This
+        // decouples the task from the thenable and allows cancelling the task.
+        if (mp_asyncio_context != MP_OBJ_NULL) {
+            mp_obj_t cur_task = mp_obj_dict_get(mp_asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR_cur_task));
+            if (cur_task != mp_const_none) {
+                mp_obj_t thenable_event_class = mp_obj_dict_get(mp_asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR_ThenableEvent));
+                mp_obj_t thenable_event = mp_call_function_1(thenable_event_class, self_in);
+                mp_obj_t dest[2];
+                mp_load_method(thenable_event, MP_QSTR_wait, dest);
+                mp_obj_t wait_gen = mp_call_method_n_kw(0, 0, dest);
+                return mp_getiter(wait_gen, iter_buf);
+            }
+        }
+        #endif
         return jsproxy_new_gen(self_in, iter_buf);
     } else {
         return jsproxy_new_it(self_in, iter_buf);
diff --git a/ports/webassembly/proxy_c.c b/ports/webassembly/proxy_c.c
index 8d137f6271..ebf670b56e 100644
--- a/ports/webassembly/proxy_c.c
+++ b/ports/webassembly/proxy_c.c
@@ -296,10 +296,11 @@ EM_JS(void, js_then_resolve, (uint32_t * ret_value, uint32_t * resolve, uint32_t
     resolve_js(ret_value_js);
 });
 
-EM_JS(void, js_then_reject, (uint32_t * resolve, uint32_t * reject), {
+EM_JS(void, js_then_reject, (uint32_t * ret_value, uint32_t * resolve, uint32_t * reject), {
+    const ret_value_js = proxy_convert_mp_to_js_obj_jsside(ret_value);
     const resolve_js = proxy_convert_mp_to_js_obj_jsside(resolve);
     const reject_js = proxy_convert_mp_to_js_obj_jsside(reject);
-    reject_js(null);
+    reject_js(ret_value_js);
 });
 
 // *FORMAT-OFF*
@@ -307,14 +308,34 @@ EM_JS(void, js_then_continue, (int jsref, uint32_t * py_resume, uint32_t * resol
     const py_resume_js = proxy_convert_mp_to_js_obj_jsside(py_resume);
     const resolve_js = proxy_convert_mp_to_js_obj_jsside(resolve);
     const reject_js = proxy_convert_mp_to_js_obj_jsside(reject);
-    const ret = proxy_js_ref[jsref].then((x) => {py_resume_js(x, resolve_js, reject_js);}, reject_js);
+    const ret = proxy_js_ref[jsref].then(
+        (result) => {
+            // The Promise is fulfilled on the JavaScript side.  Take the result and
+            // send it to the encapsulating generator on the Python side, so it
+            // becomes the result of the "yield from" that deferred to this Promise.
+            py_resume_js(result, null, resolve_js, reject_js);
+        },
+        (reason) => {
+            // The Promise is rejected on the JavaScript side.  Take the reason and
+            // throw it into the encapsulating generator on the Python side.
+            py_resume_js(null, reason, resolve_js, reject_js);
+        },
+    );
     proxy_convert_js_to_mp_obj_jsside(ret, out);
 });
 // *FORMAT-ON*
 
-static mp_obj_t proxy_resume_execute(mp_obj_t self_in, mp_obj_t value, mp_obj_t resolve, mp_obj_t reject) {
+static mp_obj_t proxy_resume_execute(mp_obj_t self_in, mp_obj_t send_value, mp_obj_t throw_value, mp_obj_t resolve, mp_obj_t reject) {
+    if (throw_value != MP_OBJ_NULL && throw_value != mp_const_none) {
+        if (send_value == mp_const_none) {
+            send_value = MP_OBJ_NULL;
+        }
+    } else {
+        throw_value = MP_OBJ_NULL;
+    }
+
     mp_obj_t ret_value;
-    mp_vm_return_kind_t ret_kind = mp_resume(self_in, value, MP_OBJ_NULL, &ret_value);
+    mp_vm_return_kind_t ret_kind = mp_resume(self_in, send_value, throw_value, &ret_value);
 
     uint32_t out_resolve[PVN];
     uint32_t out_reject[PVN];
@@ -335,17 +356,19 @@ static mp_obj_t proxy_resume_execute(mp_obj_t self_in, mp_obj_t value, mp_obj_t
         uint32_t out[PVN];
         js_then_continue(ref, out_py_resume, out_resolve, out_reject, out);
         return proxy_convert_js_to_mp_obj_cside(out);
-    } else {
-        // MP_VM_RETURN_EXCEPTION;
-        js_then_reject(out_resolve, out_reject);
-        nlr_raise(ret_value);
+    } else { // ret_kind == MP_VM_RETURN_EXCEPTION;
+        // Pass the exception through as an object to reject the promise (don't raise/throw it).
+        uint32_t out_ret_value[PVN];
+        proxy_convert_mp_to_js_obj_cside(ret_value, out_ret_value);
+        js_then_reject(out_ret_value, out_resolve, out_reject);
+        return mp_const_none;
     }
 }
 
 static mp_obj_t resume_fun(size_t n_args, const mp_obj_t *args) {
-    return proxy_resume_execute(args[0], args[1], args[2], args[3]);
+    return proxy_resume_execute(args[0], args[1], args[2], args[3], args[4]);
 }
-static MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(resume_obj, 4, 4, resume_fun);
+static MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(resume_obj, 5, 5, resume_fun);
 
 void proxy_c_to_js_resume(uint32_t c_ref, uint32_t *args) {
     nlr_buf_t nlr;
@@ -353,7 +376,7 @@ void proxy_c_to_js_resume(uint32_t c_ref, uint32_t *args) {
         mp_obj_t obj = proxy_c_get_obj(c_ref);
         mp_obj_t resolve = proxy_convert_js_to_mp_obj_cside(args + 1 * 3);
         mp_obj_t reject = proxy_convert_js_to_mp_obj_cside(args + 2 * 3);
-        mp_obj_t ret = proxy_resume_execute(obj, mp_const_none, resolve, reject);
+        mp_obj_t ret = proxy_resume_execute(obj, mp_const_none, mp_const_none, resolve, reject);
         nlr_pop();
         return proxy_convert_mp_to_js_obj_cside(ret, args);
     } else {
diff --git a/ports/webassembly/variants/manifest.py b/ports/webassembly/variants/manifest.py
new file mode 100644
index 0000000000..b2ee8cd640
--- /dev/null
+++ b/ports/webassembly/variants/manifest.py
@@ -0,0 +1,24 @@
+# The asyncio package is built from the standard implementation but with the
+# core scheduler replaced with a custom scheduler that uses the JavaScript
+# runtime (with setTimeout an Promise's) to contrtol the scheduling.
+
+package(
+    "asyncio",
+    (
+        "event.py",
+        "funcs.py",
+        "lock.py",
+    ),
+    base_path="$(MPY_DIR)/extmod",
+    opt=3,
+)
+
+package(
+    "asyncio",
+    (
+        "__init__.py",
+        "core.py",
+    ),
+    base_path="$(PORT_DIR)",
+    opt=3,
+)
diff --git a/ports/webassembly/variants/pyscript/manifest.py b/ports/webassembly/variants/pyscript/manifest.py
index 0646e1d897..db088e70d0 100644
--- a/ports/webassembly/variants/pyscript/manifest.py
+++ b/ports/webassembly/variants/pyscript/manifest.py
@@ -1,3 +1,5 @@
+include("$(PORT_DIR)/variants/manifest.py")
+
 require("abc")
 require("base64")
 require("collections")
diff --git a/py/mpconfig.h b/py/mpconfig.h
index af2480266b..1aa3e06994 100644
--- a/py/mpconfig.h
+++ b/py/mpconfig.h
@@ -587,6 +587,12 @@
 /*****************************************************************************/
 /* Python internal features                                                  */
 
+// Use a special long jump in nlrthumb.c, which may be necessary if nlr.o and
+// nlrthumb.o are linked far apart from each other.
+#ifndef MICROPY_NLR_THUMB_USE_LONG_JUMP
+#define MICROPY_NLR_THUMB_USE_LONG_JUMP (0)
+#endif
+
 // Whether to enable import of external modules
 // When disabled, only importing of built-in modules is supported
 // When enabled, a port must implement mp_import_stat (among other things)
diff --git a/py/nlrthumb.c b/py/nlrthumb.c
index a22c5df5b9..e7b24f242b 100644
--- a/py/nlrthumb.c
+++ b/py/nlrthumb.c
@@ -38,6 +38,14 @@
 
 __attribute__((naked)) unsigned int nlr_push(nlr_buf_t *nlr) {
 
+    // If you get a linker error here, indicating that a relocation doesn't
+    // fit, try the following (in that order):
+    //
+    // 1. Ensure that nlr.o nlrthumb.o are linked closely together, i.e.
+    //    there aren't too many other files between them in the linker list
+    //    (PY_CORE_O_BASENAME in py/py.mk)
+    // 2. Set -DMICROPY_NLR_THUMB_USE_LONG_JUMP=1 during the build
+    //
     __asm volatile (
         "str    r4, [r0, #12]       \n" // store r4 into nlr_buf
         "str    r5, [r0, #16]       \n" // store r5 into nlr_buf
@@ -71,7 +79,7 @@ __attribute__((naked)) unsigned int nlr_push(nlr_buf_t *nlr) {
         "str    lr, [r0, #8]        \n" // store lr into nlr_buf
         #endif
 
-        #if !defined(__thumb2__)
+        #if MICROPY_NLR_THUMB_USE_LONG_JUMP
         "ldr    r1, nlr_push_tail_var \n"
         "bx     r1                  \n" // do the rest in C
         ".align 2                   \n"
diff --git a/py/obj.h b/py/obj.h
index 9f2bb46e41..86952565c5 100644
--- a/py/obj.h
+++ b/py/obj.h
@@ -753,20 +753,20 @@ typedef struct _mp_obj_full_type_t {
 // Do not use these directly, instead use MP_DEFINE_CONST_OBJ_TYPE.
 // Generated with:
 // for i in range(13):
-//     print(f"#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_{i}(_struct_type, _typename, _name, _flags{''.join(f', f{j+1}, v{j+1}' for j in range(i))}) const _struct_type _typename = {{ .base = {{ &mp_type_type }}, .name = _name, .flags = _flags{''.join(f', .slot_index_##f{j+1} = {j+1}' for j in range(i))}{', .slots = { ' + ''.join(f'v{j+1}, ' for j in range(i)) + '}' if i else '' } }}")
-#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_0(_struct_type, _typename, _name, _flags) const _struct_type _typename = { .base = { &mp_type_type }, .name = _name, .flags = _flags }
-#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_1(_struct_type, _typename, _name, _flags, f1, v1) const _struct_type _typename = { .base = { &mp_type_type }, .name = _name, .flags = _flags, .slot_index_##f1 = 1, .slots = { v1, } }
-#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_2(_struct_type, _typename, _name, _flags, f1, v1, f2, v2) const _struct_type _typename = { .base = { &mp_type_type }, .name = _name, .flags = _flags, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slots = { v1, v2, } }
-#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_3(_struct_type, _typename, _name, _flags, f1, v1, f2, v2, f3, v3) const _struct_type _typename = { .base = { &mp_type_type }, .name = _name, .flags = _flags, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slot_index_##f3 = 3, .slots = { v1, v2, v3, } }
-#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_4(_struct_type, _typename, _name, _flags, f1, v1, f2, v2, f3, v3, f4, v4) const _struct_type _typename = { .base = { &mp_type_type }, .name = _name, .flags = _flags, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slot_index_##f3 = 3, .slot_index_##f4 = 4, .slots = { v1, v2, v3, v4, } }
-#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_5(_struct_type, _typename, _name, _flags, f1, v1, f2, v2, f3, v3, f4, v4, f5, v5) const _struct_type _typename = { .base = { &mp_type_type }, .name = _name, .flags = _flags, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slot_index_##f3 = 3, .slot_index_##f4 = 4, .slot_index_##f5 = 5, .slots = { v1, v2, v3, v4, v5, } }
-#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_6(_struct_type, _typename, _name, _flags, f1, v1, f2, v2, f3, v3, f4, v4, f5, v5, f6, v6) const _struct_type _typename = { .base = { &mp_type_type }, .name = _name, .flags = _flags, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slot_index_##f3 = 3, .slot_index_##f4 = 4, .slot_index_##f5 = 5, .slot_index_##f6 = 6, .slots = { v1, v2, v3, v4, v5, v6, } }
-#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_7(_struct_type, _typename, _name, _flags, f1, v1, f2, v2, f3, v3, f4, v4, f5, v5, f6, v6, f7, v7) const _struct_type _typename = { .base = { &mp_type_type }, .name = _name, .flags = _flags, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slot_index_##f3 = 3, .slot_index_##f4 = 4, .slot_index_##f5 = 5, .slot_index_##f6 = 6, .slot_index_##f7 = 7, .slots = { v1, v2, v3, v4, v5, v6, v7, } }
-#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_8(_struct_type, _typename, _name, _flags, f1, v1, f2, v2, f3, v3, f4, v4, f5, v5, f6, v6, f7, v7, f8, v8) const _struct_type _typename = { .base = { &mp_type_type }, .name = _name, .flags = _flags, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slot_index_##f3 = 3, .slot_index_##f4 = 4, .slot_index_##f5 = 5, .slot_index_##f6 = 6, .slot_index_##f7 = 7, .slot_index_##f8 = 8, .slots = { v1, v2, v3, v4, v5, v6, v7, v8, } }
-#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_9(_struct_type, _typename, _name, _flags, f1, v1, f2, v2, f3, v3, f4, v4, f5, v5, f6, v6, f7, v7, f8, v8, f9, v9) const _struct_type _typename = { .base = { &mp_type_type }, .name = _name, .flags = _flags, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slot_index_##f3 = 3, .slot_index_##f4 = 4, .slot_index_##f5 = 5, .slot_index_##f6 = 6, .slot_index_##f7 = 7, .slot_index_##f8 = 8, .slot_index_##f9 = 9, .slots = { v1, v2, v3, v4, v5, v6, v7, v8, v9, } }
-#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_10(_struct_type, _typename, _name, _flags, f1, v1, f2, v2, f3, v3, f4, v4, f5, v5, f6, v6, f7, v7, f8, v8, f9, v9, f10, v10) const _struct_type _typename = { .base = { &mp_type_type }, .name = _name, .flags = _flags, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slot_index_##f3 = 3, .slot_index_##f4 = 4, .slot_index_##f5 = 5, .slot_index_##f6 = 6, .slot_index_##f7 = 7, .slot_index_##f8 = 8, .slot_index_##f9 = 9, .slot_index_##f10 = 10, .slots = { v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, } }
-#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_11(_struct_type, _typename, _name, _flags, f1, v1, f2, v2, f3, v3, f4, v4, f5, v5, f6, v6, f7, v7, f8, v8, f9, v9, f10, v10, f11, v11) const _struct_type _typename = { .base = { &mp_type_type }, .name = _name, .flags = _flags, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slot_index_##f3 = 3, .slot_index_##f4 = 4, .slot_index_##f5 = 5, .slot_index_##f6 = 6, .slot_index_##f7 = 7, .slot_index_##f8 = 8, .slot_index_##f9 = 9, .slot_index_##f10 = 10, .slot_index_##f11 = 11, .slots = { v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, } }
-#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_12(_struct_type, _typename, _name, _flags, f1, v1, f2, v2, f3, v3, f4, v4, f5, v5, f6, v6, f7, v7, f8, v8, f9, v9, f10, v10, f11, v11, f12, v12) const _struct_type _typename = { .base = { &mp_type_type }, .name = _name, .flags = _flags, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slot_index_##f3 = 3, .slot_index_##f4 = 4, .slot_index_##f5 = 5, .slot_index_##f6 = 6, .slot_index_##f7 = 7, .slot_index_##f8 = 8, .slot_index_##f9 = 9, .slot_index_##f10 = 10, .slot_index_##f11 = 11, .slot_index_##f12 = 12, .slots = { v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, } }
+//     print(f"#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_{i}(_struct_type, _typename, _name, _flags{''.join(f', f{j+1}, v{j+1}' for j in range(i))}) const _struct_type _typename = {{ .base = {{ &mp_type_type }}, .flags = _flags, .name = _name{''.join(f', .slot_index_##f{j+1} = {j+1}' for j in range(i))}{', .slots = { ' + ''.join(f'v{j+1}, ' for j in range(i)) + '}' if i else '' } }}")
+#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_0(_struct_type, _typename, _name, _flags) const _struct_type _typename = { .base = { &mp_type_type }, .flags = _flags, .name = _name }
+#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_1(_struct_type, _typename, _name, _flags, f1, v1) const _struct_type _typename = { .base = { &mp_type_type }, .flags = _flags, .name = _name, .slot_index_##f1 = 1, .slots = { v1, } }
+#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_2(_struct_type, _typename, _name, _flags, f1, v1, f2, v2) const _struct_type _typename = { .base = { &mp_type_type }, .flags = _flags, .name = _name, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slots = { v1, v2, } }
+#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_3(_struct_type, _typename, _name, _flags, f1, v1, f2, v2, f3, v3) const _struct_type _typename = { .base = { &mp_type_type }, .flags = _flags, .name = _name, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slot_index_##f3 = 3, .slots = { v1, v2, v3, } }
+#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_4(_struct_type, _typename, _name, _flags, f1, v1, f2, v2, f3, v3, f4, v4) const _struct_type _typename = { .base = { &mp_type_type }, .flags = _flags, .name = _name, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slot_index_##f3 = 3, .slot_index_##f4 = 4, .slots = { v1, v2, v3, v4, } }
+#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_5(_struct_type, _typename, _name, _flags, f1, v1, f2, v2, f3, v3, f4, v4, f5, v5) const _struct_type _typename = { .base = { &mp_type_type }, .flags = _flags, .name = _name, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slot_index_##f3 = 3, .slot_index_##f4 = 4, .slot_index_##f5 = 5, .slots = { v1, v2, v3, v4, v5, } }
+#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_6(_struct_type, _typename, _name, _flags, f1, v1, f2, v2, f3, v3, f4, v4, f5, v5, f6, v6) const _struct_type _typename = { .base = { &mp_type_type }, .flags = _flags, .name = _name, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slot_index_##f3 = 3, .slot_index_##f4 = 4, .slot_index_##f5 = 5, .slot_index_##f6 = 6, .slots = { v1, v2, v3, v4, v5, v6, } }
+#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_7(_struct_type, _typename, _name, _flags, f1, v1, f2, v2, f3, v3, f4, v4, f5, v5, f6, v6, f7, v7) const _struct_type _typename = { .base = { &mp_type_type }, .flags = _flags, .name = _name, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slot_index_##f3 = 3, .slot_index_##f4 = 4, .slot_index_##f5 = 5, .slot_index_##f6 = 6, .slot_index_##f7 = 7, .slots = { v1, v2, v3, v4, v5, v6, v7, } }
+#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_8(_struct_type, _typename, _name, _flags, f1, v1, f2, v2, f3, v3, f4, v4, f5, v5, f6, v6, f7, v7, f8, v8) const _struct_type _typename = { .base = { &mp_type_type }, .flags = _flags, .name = _name, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slot_index_##f3 = 3, .slot_index_##f4 = 4, .slot_index_##f5 = 5, .slot_index_##f6 = 6, .slot_index_##f7 = 7, .slot_index_##f8 = 8, .slots = { v1, v2, v3, v4, v5, v6, v7, v8, } }
+#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_9(_struct_type, _typename, _name, _flags, f1, v1, f2, v2, f3, v3, f4, v4, f5, v5, f6, v6, f7, v7, f8, v8, f9, v9) const _struct_type _typename = { .base = { &mp_type_type }, .flags = _flags, .name = _name, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slot_index_##f3 = 3, .slot_index_##f4 = 4, .slot_index_##f5 = 5, .slot_index_##f6 = 6, .slot_index_##f7 = 7, .slot_index_##f8 = 8, .slot_index_##f9 = 9, .slots = { v1, v2, v3, v4, v5, v6, v7, v8, v9, } }
+#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_10(_struct_type, _typename, _name, _flags, f1, v1, f2, v2, f3, v3, f4, v4, f5, v5, f6, v6, f7, v7, f8, v8, f9, v9, f10, v10) const _struct_type _typename = { .base = { &mp_type_type }, .flags = _flags, .name = _name, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slot_index_##f3 = 3, .slot_index_##f4 = 4, .slot_index_##f5 = 5, .slot_index_##f6 = 6, .slot_index_##f7 = 7, .slot_index_##f8 = 8, .slot_index_##f9 = 9, .slot_index_##f10 = 10, .slots = { v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, } }
+#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_11(_struct_type, _typename, _name, _flags, f1, v1, f2, v2, f3, v3, f4, v4, f5, v5, f6, v6, f7, v7, f8, v8, f9, v9, f10, v10, f11, v11) const _struct_type _typename = { .base = { &mp_type_type }, .flags = _flags, .name = _name, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slot_index_##f3 = 3, .slot_index_##f4 = 4, .slot_index_##f5 = 5, .slot_index_##f6 = 6, .slot_index_##f7 = 7, .slot_index_##f8 = 8, .slot_index_##f9 = 9, .slot_index_##f10 = 10, .slot_index_##f11 = 11, .slots = { v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, } }
+#define MP_DEFINE_CONST_OBJ_TYPE_NARGS_12(_struct_type, _typename, _name, _flags, f1, v1, f2, v2, f3, v3, f4, v4, f5, v5, f6, v6, f7, v7, f8, v8, f9, v9, f10, v10, f11, v11, f12, v12) const _struct_type _typename = { .base = { &mp_type_type }, .flags = _flags, .name = _name, .slot_index_##f1 = 1, .slot_index_##f2 = 2, .slot_index_##f3 = 3, .slot_index_##f4 = 4, .slot_index_##f5 = 5, .slot_index_##f6 = 6, .slot_index_##f7 = 7, .slot_index_##f8 = 8, .slot_index_##f9 = 9, .slot_index_##f10 = 10, .slot_index_##f11 = 11, .slot_index_##f12 = 12, .slots = { v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, } }
 
 // Because the mp_obj_type_t instances are in (zero-initialised) ROM, we take
 // slot_index_foo=0 to mean that the slot is unset. This also simplifies checking
diff --git a/py/objarray.c b/py/objarray.c
index 1fff234822..803af2cd27 100644
--- a/py/objarray.c
+++ b/py/objarray.c
@@ -424,6 +424,13 @@ static mp_obj_t array_extend(mp_obj_t self_in, mp_obj_t arg_in) {
     if (self->free < len) {
         self->items = m_renew(byte, self->items, (self->len + self->free) * sz, (self->len + len) * sz);
         self->free = 0;
+
+        if (self_in == arg_in) {
+            // Get arg_bufinfo again in case self->items has moved
+            //
+            // (Note not possible to handle case that arg_in is a memoryview into self)
+            mp_get_buffer_raise(arg_in, &arg_bufinfo, MP_BUFFER_READ);
+        }
     } else {
         self->free -= len;
     }
@@ -456,7 +463,8 @@ static mp_obj_t array_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value
                 #if MICROPY_PY_ARRAY_SLICE_ASSIGN
                 // Assign
                 size_t src_len;
-                void *src_items;
+                uint8_t *src_items;
+                size_t src_offs = 0;
                 size_t item_sz = mp_binary_get_size('@', o->typecode & TYPECODE_MASK, NULL);
                 if (mp_obj_is_obj(value) && MP_OBJ_TYPE_GET_SLOT_OR_NULL(((mp_obj_base_t *)MP_OBJ_TO_PTR(value))->type, subscr) == array_subscr) {
                     // value is array, bytearray or memoryview
@@ -469,7 +477,7 @@ static mp_obj_t array_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value
                     src_items = src_slice->items;
                     #if MICROPY_PY_BUILTINS_MEMORYVIEW
                     if (mp_obj_is_type(value, &mp_type_memoryview)) {
-                        src_items = (uint8_t *)src_items + (src_slice->memview_offset * item_sz);
+                        src_offs = src_slice->memview_offset * item_sz;
                     }
                     #endif
                 } else if (mp_obj_is_type(value, &mp_type_bytes)) {
@@ -504,13 +512,17 @@ static mp_obj_t array_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value
                         // TODO: alloc policy; at the moment we go conservative
                         o->items = m_renew(byte, o->items, (o->len + o->free) * item_sz, (o->len + len_adj) * item_sz);
                         o->free = len_adj;
+                        // m_renew may have moved o->items
+                        if (src_items == dest_items) {
+                            src_items = o->items;
+                        }
                         dest_items = o->items;
                     }
                     mp_seq_replace_slice_grow_inplace(dest_items, o->len,
-                        slice.start, slice.stop, src_items, src_len, len_adj, item_sz);
+                        slice.start, slice.stop, src_items + src_offs, src_len, len_adj, item_sz);
                 } else {
                     mp_seq_replace_slice_no_grow(dest_items, o->len,
-                        slice.start, slice.stop, src_items, src_len, item_sz);
+                        slice.start, slice.stop, src_items + src_offs, src_len, item_sz);
                     // Clear "freed" elements at the end of list
                     // TODO: This is actually only needed for typecode=='O'
                     mp_seq_clear(dest_items, o->len + len_adj, o->len, item_sz);
diff --git a/py/objfun.h b/py/objfun.h
index af7c334858..f16ef76b80 100644
--- a/py/objfun.h
+++ b/py/objfun.h
@@ -56,14 +56,14 @@ void mp_obj_fun_bc_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest);
 #if MICROPY_EMIT_NATIVE
 
 static inline mp_obj_t mp_obj_new_fun_native(const mp_obj_t *def_args, const void *fun_data, const mp_module_context_t *mc, struct _mp_raw_code_t *const *child_table) {
-    mp_obj_fun_bc_t *o = MP_OBJ_TO_PTR(mp_obj_new_fun_bc(def_args, (const byte *)fun_data, mc, child_table));
+    mp_obj_fun_bc_t *o = (mp_obj_fun_bc_t *)MP_OBJ_TO_PTR(mp_obj_new_fun_bc(def_args, (const byte *)fun_data, mc, child_table));
     o->base.type = &mp_type_fun_native;
     return MP_OBJ_FROM_PTR(o);
 }
 
 static inline mp_obj_t mp_obj_new_fun_viper(const void *fun_data, const mp_module_context_t *mc, struct _mp_raw_code_t *const *child_table) {
     mp_obj_fun_bc_t *o = mp_obj_malloc(mp_obj_fun_bc_t, &mp_type_fun_viper);
-    o->bytecode = fun_data;
+    o->bytecode = (const byte *)fun_data;
     o->context = mc;
     o->child_table = child_table;
     return MP_OBJ_FROM_PTR(o);
@@ -101,9 +101,9 @@ static inline void *mp_obj_fun_native_get_generator_resume(const mp_obj_fun_bc_t
 
 #if MICROPY_EMIT_INLINE_ASM
 static inline mp_obj_t mp_obj_new_fun_asm(size_t n_args, const void *fun_data, mp_uint_t type_sig) {
-    mp_obj_fun_asm_t *o = mp_obj_malloc(mp_obj_fun_asm_t, &mp_type_fun_asm);
+    mp_obj_fun_asm_t *o = (mp_obj_fun_asm_t *)mp_obj_malloc(mp_obj_fun_asm_t, &mp_type_fun_asm);
     o->n_args = n_args;
-    o->fun_data = fun_data;
+    o->fun_data = (const byte *)fun_data;
     o->type_sig = type_sig;
     return MP_OBJ_FROM_PTR(o);
 }
diff --git a/tests/basics/bytearray_add.py b/tests/basics/bytearray_add.py
index a7e2b57374..1f30a3b740 100644
--- a/tests/basics/bytearray_add.py
+++ b/tests/basics/bytearray_add.py
@@ -15,4 +15,11 @@ print(b)
 
 # this inplace add tests the code when the buffer doesn't need to be increased
 b = bytearray()
-b += b''
+b += b""
+
+# extend a bytearray from itself
+b = bytearray(b"abcdefgh")
+for _ in range(4):
+    c = bytearray(b)  # extra allocation, as above
+    b.extend(b)
+print(b)
diff --git a/tests/basics/bytearray_add_self.py b/tests/basics/bytearray_add_self.py
new file mode 100644
index 0000000000..94ae8689fd
--- /dev/null
+++ b/tests/basics/bytearray_add_self.py
@@ -0,0 +1,8 @@
+# add a bytearray to itself
+# This is not supported by CPython as of 3.11.18.
+
+b = bytearray(b"123456789")
+for _ in range(4):
+    c = bytearray(b)  # extra allocation increases chance 'b' has to relocate
+    b += b
+print(b)
diff --git a/tests/basics/bytearray_add_self.py.exp b/tests/basics/bytearray_add_self.py.exp
new file mode 100644
index 0000000000..5ef948157a
--- /dev/null
+++ b/tests/basics/bytearray_add_self.py.exp
@@ -0,0 +1 @@
+bytearray(b'123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789123456789')
diff --git a/tests/basics/bytearray_slice_assign.py b/tests/basics/bytearray_slice_assign.py
index fa7878e10d..4de0819042 100644
--- a/tests/basics/bytearray_slice_assign.py
+++ b/tests/basics/bytearray_slice_assign.py
@@ -18,7 +18,7 @@ l = bytearray(x)
 l[1:3] = bytearray()
 print(l)
 l = bytearray(x)
-#del l[1:3]
+# del l[1:3]
 print(l)
 
 l = bytearray(x)
@@ -28,7 +28,7 @@ l = bytearray(x)
 l[:3] = bytearray()
 print(l)
 l = bytearray(x)
-#del l[:3]
+# del l[:3]
 print(l)
 
 l = bytearray(x)
@@ -38,7 +38,7 @@ l = bytearray(x)
 l[:-3] = bytearray()
 print(l)
 l = bytearray(x)
-#del l[:-3]
+# del l[:-3]
 print(l)
 
 # slice assignment that extends the array
@@ -61,8 +61,14 @@ b[1:1] = b"12345"
 print(b)
 
 # Growth of bytearray via slice extension
-b = bytearray(b'12345678')
-b.append(57) # expand and add a bit of unused space at end of the bytearray
+b = bytearray(b"12345678")
+b.append(57)  # expand and add a bit of unused space at end of the bytearray
 for i in range(400):
-    b[-1:] = b'ab' # grow slowly into the unused space
+    b[-1:] = b"ab"  # grow slowly into the unused space
+print(len(b), b)
+
+# Growth of bytearray via slice extension from itself
+b = bytearray(b"1234567")
+for i in range(3):
+    b[-1:] = b
 print(len(b), b)
diff --git a/tests/cpydiff/types_memoryview_invalid.py b/tests/cpydiff/types_memoryview_invalid.py
new file mode 100644
index 0000000000..c995a2e899
--- /dev/null
+++ b/tests/cpydiff/types_memoryview_invalid.py
@@ -0,0 +1,12 @@
+"""
+categories: Types,memoryview
+description: memoryview can become invalid if its target is resized
+cause: CPython prevents a ``bytearray`` or ``io.bytesIO`` object from changing size while there is a ``memoryview`` object that references it. MicroPython requires the programmer to manually ensure that an object is not resized while any ``memoryview`` references it.
+
+In the worst case scenario, resizing an object which is the target of a memoryview can cause the memoryview(s) to reference invalid freed memory (a use-after-free bug) and corrupt the MicroPython runtime.
+workaround: Do not change the size of any ``bytearray`` or ``io.bytesIO`` object that has a ``memoryview`` assigned to it.
+"""
+b = bytearray(b"abcdefg")
+m = memoryview(b)
+b.extend(b"hijklmnop")
+print(b, bytes(m))
diff --git a/tests/ports/webassembly/asyncio_create_task.mjs b/tests/ports/webassembly/asyncio_create_task.mjs
new file mode 100644
index 0000000000..e388ade4f1
--- /dev/null
+++ b/tests/ports/webassembly/asyncio_create_task.mjs
@@ -0,0 +1,44 @@
+// Test asyncio.create_task(), and tasks waiting on a Promise.
+
+const mp = await (await import(process.argv[2])).loadMicroPython();
+
+globalThis.p0 = new Promise((resolve, reject) => {
+    resolve(123);
+});
+
+globalThis.p1 = new Promise((resolve, reject) => {
+    setTimeout(() => {
+        console.log("setTimeout resolved");
+        resolve(456);
+    }, 200);
+});
+
+mp.runPython(`
+import js
+import asyncio
+
+async def task(id, promise):
+    print("task start", id)
+    print("task await", id, await promise)
+    print("task await", id, await promise)
+    print("task end", id)
+
+print("start")
+t1 = asyncio.create_task(task(1, js.p0))
+t2 = asyncio.create_task(task(2, js.p1))
+print("t1", t1.done(), t2.done())
+print("end")
+`);
+
+// Wait for p1 to fulfill so t2 can continue.
+await globalThis.p1;
+
+// Wait a little longer so t2 can complete.
+await new Promise((resolve, reject) => {
+    setTimeout(resolve, 10);
+});
+
+mp.runPython(`
+print("restart")
+print("t1", t1.done(), t2.done())
+`);
diff --git a/tests/ports/webassembly/asyncio_create_task.mjs.exp b/tests/ports/webassembly/asyncio_create_task.mjs.exp
new file mode 100644
index 0000000000..c1958bba59
--- /dev/null
+++ b/tests/ports/webassembly/asyncio_create_task.mjs.exp
@@ -0,0 +1,14 @@
+start
+t1 False False
+end
+task start 1
+task start 2
+task await 1 123
+task await 1 123
+task end 1
+setTimeout resolved
+task await 2 456
+task await 2 456
+task end 2
+restart
+t1 True True
diff --git a/tests/ports/webassembly/asyncio_sleep.mjs b/tests/ports/webassembly/asyncio_sleep.mjs
new file mode 100644
index 0000000000..74d22ee1f8
--- /dev/null
+++ b/tests/ports/webassembly/asyncio_sleep.mjs
@@ -0,0 +1,25 @@
+// Test asyncio.sleep(), both at the top level and within a task.
+
+const mp = await (await import(process.argv[2])).loadMicroPython();
+
+await mp.runPythonAsync(`
+import time
+import asyncio
+
+print("main start")
+t0 = time.time()
+await asyncio.sleep(0.25)
+dt = time.time() - t0
+print(0.2 <= dt <= 0.3)
+
+async def task():
+    print("task start")
+    t0 = time.time()
+    await asyncio.sleep(0.25)
+    dt = time.time() - t0
+    print(0.2 <= dt <= 0.3)
+    print("task end")
+
+asyncio.create_task(task())
+print("main end")
+`);
diff --git a/tests/ports/webassembly/asyncio_sleep.mjs.exp b/tests/ports/webassembly/asyncio_sleep.mjs.exp
new file mode 100644
index 0000000000..619ba175f6
--- /dev/null
+++ b/tests/ports/webassembly/asyncio_sleep.mjs.exp
@@ -0,0 +1,6 @@
+main start
+True
+main end
+task start
+True
+task end
diff --git a/tests/run-tests.py b/tests/run-tests.py
index 4f55cdd398..8acdcd2b36 100755
--- a/tests/run-tests.py
+++ b/tests/run-tests.py
@@ -681,6 +681,17 @@ def run_tests(pyb, tests, args, result_dir, num_threads=1):
         elif args.target == "webassembly":
             skip_tests.add("basics/string_format_modulo.py")  # can't print nulls to stdout
             skip_tests.add("basics/string_strip.py")  # can't print nulls to stdout
+            skip_tests.add("extmod/asyncio_basic2.py")
+            skip_tests.add("extmod/asyncio_cancel_self.py")
+            skip_tests.add("extmod/asyncio_current_task.py")
+            skip_tests.add("extmod/asyncio_exception.py")
+            skip_tests.add("extmod/asyncio_gather_finished_early.py")
+            skip_tests.add("extmod/asyncio_get_event_loop.py")
+            skip_tests.add("extmod/asyncio_heaplock.py")
+            skip_tests.add("extmod/asyncio_loop_stop.py")
+            skip_tests.add("extmod/asyncio_new_event_loop.py")
+            skip_tests.add("extmod/asyncio_threadsafeflag.py")
+            skip_tests.add("extmod/asyncio_wait_for_fwd.py")
             skip_tests.add("extmod/binascii_a2b_base64.py")
             skip_tests.add("extmod/re_stack_overflow.py")
             skip_tests.add("extmod/time_res.py")