diff --git a/extmod/btstack/btstack.mk b/extmod/btstack/btstack.mk
index 17bbb16f88..9e1857263b 100644
--- a/extmod/btstack/btstack.mk
+++ b/extmod/btstack/btstack.mk
@@ -30,7 +30,6 @@ INC += -I$(BTSTACK_DIR)/3rd-party/yxml
 SRC_BTSTACK = \
 	$(addprefix lib/btstack/src/, $(SRC_FILES)) \
 	$(addprefix lib/btstack/src/ble/, $(filter-out %_tlv.c, $(SRC_BLE_FILES))) \
-	lib/btstack/platform/embedded/btstack_run_loop_embedded.c
 
 ifeq ($(MICROPY_BLUETOOTH_BTSTACK_USB),1)
 ifeq ($(MICROPY_BLUETOOTH_BTSTACK_H4),1)
diff --git a/ports/stm32/mpbtstackport.c b/ports/stm32/mpbtstackport.c
index abe4f6d3e2..795534042e 100644
--- a/ports/stm32/mpbtstackport.c
+++ b/ports/stm32/mpbtstackport.c
@@ -3,7 +3,7 @@
  *
  * The MIT License (MIT)
  *
- * Copyright (c) 2020 Damien P. George
+ * Copyright (c) 2020-2021 Damien P. George
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -31,31 +31,79 @@
 #if MICROPY_PY_BLUETOOTH && MICROPY_BLUETOOTH_BTSTACK
 
 #include "lib/btstack/src/btstack.h"
-#include "lib/btstack/platform/embedded/btstack_run_loop_embedded.h"
-#include "lib/btstack/platform/embedded/hal_cpu.h"
-#include "lib/btstack/platform/embedded/hal_time_ms.h"
-
 #include "extmod/mpbthci.h"
 #include "extmod/btstack/btstack_hci_uart.h"
 #include "extmod/btstack/modbluetooth_btstack.h"
 #include "mpbthciport.h"
 
-// The IRQ functionality in btstack_run_loop_embedded.c is not used, so the
-// following three functions are empty.
+void mp_bluetooth_hci_poll_in_ms(uint32_t ms);
 
-void hal_cpu_disable_irqs(void) {
+static btstack_linked_list_t mp_btstack_runloop_timers;
+
+static void mp_btstack_runloop_init(void) {
+    mp_btstack_runloop_timers = NULL;
 }
 
-void hal_cpu_enable_irqs(void) {
+static void mp_btstack_runloop_set_timer(btstack_timer_source_t *tim, uint32_t timeout_ms) {
+    tim->timeout = mp_hal_ticks_ms() + timeout_ms + 1;
 }
 
-void hal_cpu_enable_irqs_and_sleep(void) {
+static void mp_btstack_runloop_add_timer(btstack_timer_source_t *tim) {
+    btstack_linked_item_t **node = &mp_btstack_runloop_timers;
+    for (; *node; node = &(*node)->next) {
+        btstack_timer_source_t *node_tim = (btstack_timer_source_t *)*node;
+        if (node_tim == tim) {
+            // Timer is already in the list, don't add it.
+            return;
+        }
+        int32_t delta = btstack_time_delta(tim->timeout, node_tim->timeout);
+        if (delta < 0) {
+            // Found sorted location in list.
+            break;
+        }
+    }
+
+    // Insert timer into list in sorted location.
+    tim->item.next = *node;
+    *node = &tim->item;
+
+    // Reschedule the HCI poll if this timer is at the head of the list.
+    if (mp_btstack_runloop_timers == &tim->item) {
+        int32_t delta_ms = btstack_time_delta(tim->timeout, mp_hal_ticks_ms());
+        mp_bluetooth_hci_poll_in_ms(delta_ms);
+    }
 }
 
-uint32_t hal_time_ms(void) {
+static bool mp_btstack_runloop_remove_timer(btstack_timer_source_t *tim) {
+    return btstack_linked_list_remove(&mp_btstack_runloop_timers, (btstack_linked_item_t *)tim);
+}
+
+static void mp_btstack_runloop_execute(void) {
+    // Should not be called.
+}
+
+static void mp_btstack_runloop_dump_timer(void) {
+    // Not implemented/needed.
+}
+
+static uint32_t mp_btstack_runloop_get_time_ms(void) {
     return mp_hal_ticks_ms();
 }
 
+static const btstack_run_loop_t mp_btstack_runloop_stm32 = {
+    &mp_btstack_runloop_init,
+    NULL, // add_data_source,
+    NULL, // remove_data_source,
+    NULL, // enable_data_source_callbacks,
+    NULL, // disable_data_source_callbacks,
+    &mp_btstack_runloop_set_timer,
+    &mp_btstack_runloop_add_timer,
+    &mp_btstack_runloop_remove_timer,
+    &mp_btstack_runloop_execute,
+    &mp_btstack_runloop_dump_timer,
+    &mp_btstack_runloop_get_time_ms,
+};
+
 STATIC const hci_transport_config_uart_t hci_transport_config_uart = {
     HCI_TRANSPORT_CONFIG_UART,
     MICROPY_HW_BLE_UART_BAUDRATE,
@@ -69,26 +117,32 @@ void mp_bluetooth_hci_poll(void) {
         return;
     }
 
-    // Process uart data.
+    // Process UART data.
     if (mp_bluetooth_btstack_state != MP_BLUETOOTH_BTSTACK_STATE_HALTING) {
         mp_bluetooth_btstack_hci_uart_process();
     }
 
-    // Call the BTstack run loop.
-    btstack_run_loop_embedded_execute_once();
-
-    // Call this function again in 128ms to check for new events.
-    // TODO: improve this by only calling back when needed.
-    mp_bluetooth_hci_poll_in_ms(128);
+    // Process any BTstack timers.
+    while (mp_btstack_runloop_timers != NULL) {
+        btstack_timer_source_t *tim = (btstack_timer_source_t *)mp_btstack_runloop_timers;
+        int32_t delta_ms = btstack_time_delta(tim->timeout, mp_hal_ticks_ms());
+        if (delta_ms > 0) {
+            // Timer has not expired yet, reschedule HCI poll for this timer.
+            mp_bluetooth_hci_poll_in_ms(delta_ms);
+            break;
+        }
+        btstack_linked_list_pop(&mp_btstack_runloop_timers);
+        tim->process(tim);
+    }
 }
 
 void mp_bluetooth_btstack_port_init(void) {
     static bool run_loop_init = false;
     if (!run_loop_init) {
         run_loop_init = true;
-        btstack_run_loop_init(btstack_run_loop_embedded_get_instance());
+        btstack_run_loop_init(&mp_btstack_runloop_stm32);
     } else {
-        btstack_run_loop_embedded_get_instance()->init();
+        mp_btstack_runloop_stm32.init();
     }
 
     // hci_dump_open(NULL, HCI_DUMP_STDOUT);
diff --git a/ports/unix/Makefile b/ports/unix/Makefile
index fe86018aa0..d97e4bc7e0 100644
--- a/ports/unix/Makefile
+++ b/ports/unix/Makefile
@@ -177,6 +177,7 @@ endif
 # BTstack is enabled.
 GIT_SUBMODULES += lib/btstack
 include $(TOP)/extmod/btstack/btstack.mk
+SRC_BTSTACK += lib/btstack/platform/embedded/btstack_run_loop_embedded.c
 
 else