diff --git a/extmod/nimble/modbluetooth_nimble.c b/extmod/nimble/modbluetooth_nimble.c
index 4222f58fa..9ca90b602 100644
--- a/extmod/nimble/modbluetooth_nimble.c
+++ b/extmod/nimble/modbluetooth_nimble.c
@@ -52,6 +52,9 @@
 
 STATIC uint8_t nimble_address_mode = BLE_OWN_ADDR_RANDOM;
 
+#define NIMBLE_STARTUP_TIMEOUT 2000
+STATIC struct ble_npl_sem startup_sem;
+
 // Any BLE_HS_xxx code not in this table will default to MP_EIO.
 STATIC int8_t ble_hs_err_to_errno_table[] = {
     [BLE_HS_EAGAIN] = MP_EAGAIN,
@@ -206,6 +209,8 @@ STATIC void sync_cb(void) {
     ble_svc_gap_device_name_set(MICROPY_PY_BLUETOOTH_DEFAULT_GAP_NAME);
 
     mp_bluetooth_nimble_ble_state = MP_BLUETOOTH_NIMBLE_BLE_STATE_ACTIVE;
+
+    ble_npl_sem_release(&startup_sem);
 }
 
 STATIC void gatts_register_cb(struct ble_gatt_register_ctxt *ctxt, void *arg) {
@@ -355,6 +360,8 @@ int mp_bluetooth_init(void) {
     ble_hs_cfg.gatts_register_cb = gatts_register_cb;
     ble_hs_cfg.store_status_cb = ble_store_util_status_rr;
 
+    ble_npl_sem_init(&startup_sem, 0);
+
     MP_STATE_PORT(bluetooth_nimble_root_pointers) = m_new0(mp_bluetooth_nimble_root_pointers_t, 1);
     mp_bluetooth_gatts_db_create(&MP_STATE_PORT(bluetooth_nimble_root_pointers)->gatts_db);
 
@@ -370,21 +377,28 @@ int mp_bluetooth_init(void) {
     // Initialise NimBLE memory and data structures.
     nimble_port_init();
 
-    // By default, just register the default gap/gatt service.
-    ble_svc_gap_init();
-    ble_svc_gatt_init();
-
     // Make sure that the HCI UART and event handling task is running.
     mp_bluetooth_nimble_port_start();
 
     // Static initialization is complete, can start processing events.
     mp_bluetooth_nimble_ble_state = MP_BLUETOOTH_NIMBLE_BLE_STATE_WAITING_FOR_SYNC;
 
-    // Wait for sync callback
-    while (mp_bluetooth_nimble_ble_state != MP_BLUETOOTH_NIMBLE_BLE_STATE_ACTIVE) {
-        MICROPY_EVENT_POLL_HOOK
+    ble_npl_sem_pend(&startup_sem, NIMBLE_STARTUP_TIMEOUT);
+
+    if (mp_bluetooth_nimble_ble_state != MP_BLUETOOTH_NIMBLE_BLE_STATE_ACTIVE) {
+        mp_bluetooth_deinit();
+        return MP_ETIMEDOUT;
     }
 
+    // By default, just register the default gap/gatt service.
+    ble_svc_gap_init();
+    ble_svc_gatt_init();
+    // The preceeding two calls allocate service definitions on the heap,
+    // then we must now call gatts_start to register those services
+    // and free the heap memory.
+    // Otherwise it will be realloc'ed on the next stack startup.
+    ble_gatts_start();
+
     DEBUG_printf("mp_bluetooth_init: ready\n");
 
     return 0;
diff --git a/extmod/nimble/nimble/nimble_npl_os.c b/extmod/nimble/nimble/nimble_npl_os.c
index 46f7a0b29..2ec012940 100644
--- a/extmod/nimble/nimble/nimble_npl_os.c
+++ b/extmod/nimble/nimble/nimble_npl_os.c
@@ -32,6 +32,7 @@
 #include "extmod/nimble/hal/hal_uart.h"
 
 #include "extmod/modbluetooth.h"
+#include "extmod/nimble/modbluetooth_nimble.h"
 
 #define DEBUG_OS_printf(...) // printf(__VA_ARGS__)
 #define DEBUG_MALLOC_printf(...) // printf(__VA_ARGS__)
@@ -180,7 +181,8 @@ struct ble_npl_eventq *global_eventq = NULL;
 
 void mp_bluetooth_nimble_os_eventq_run_all(void) {
     for (struct ble_npl_eventq *evq = global_eventq; evq != NULL; evq = evq->nextq) {
-        while (evq->head != NULL) {
+        int n = 0;
+        while (evq->head != NULL && mp_bluetooth_nimble_ble_state > MP_BLUETOOTH_NIMBLE_BLE_STATE_OFF) {
             struct ble_npl_event *ev = evq->head;
             evq->head = ev->next;
             if (ev->next) {
@@ -191,6 +193,13 @@ void mp_bluetooth_nimble_os_eventq_run_all(void) {
             DEBUG_EVENT_printf("event_run(%p)\n", ev);
             ev->fn(ev);
             DEBUG_EVENT_printf("event_run(%p) done\n", ev);
+
+            if (++n > 3) {
+                // Limit to running 3 tasks per queue.
+                // Some tasks (such as reset) can enqueue themselves
+                // making this an infinite loop (while in PENDSV).
+                break;
+            }
         }
     }
 }
@@ -348,11 +357,11 @@ ble_npl_error_t ble_npl_sem_pend(struct ble_npl_sem *sem, ble_npl_time_t timeout
         }
 
         if (sem->count == 0) {
-            printf("NimBLE: HCI ACK timeout\n");
+            DEBUG_SEM_printf("ble_npl_sem_pend: semaphore timeout\n");
             return BLE_NPL_TIMEOUT;
         }
 
-        DEBUG_SEM_printf("got response in %u ms\n", (int)(mp_hal_ticks_ms() - t0));
+        DEBUG_SEM_printf("ble_npl_sem_pend: acquired in %u ms\n", (int)(mp_hal_ticks_ms() - t0));
     }
     sem->count -= 1;
     return BLE_NPL_OK;
diff --git a/ports/unix/mpbthciport.c b/ports/unix/mpbthciport.c
index dbfb5e0d0..316a8831f 100644
--- a/ports/unix/mpbthciport.c
+++ b/ports/unix/mpbthciport.c
@@ -105,6 +105,10 @@ STATIC int configure_uart(void) {
     // Apply immediately.
     if (tcsetattr(uart_fd, TCSANOW, &toptions) < 0) {
         DEBUG_printf("Couldn't set term attributes");
+
+        close(uart_fd);
+        uart_fd = -1;
+
         return -1;
     }
 
@@ -149,6 +153,10 @@ int mp_bluetooth_hci_uart_init(uint32_t port, uint32_t baudrate) {
 int mp_bluetooth_hci_uart_deinit(void) {
     DEBUG_printf("mp_bluetooth_hci_uart_deinit\n");
 
+    if (uart_fd == -1) {
+        return 0;
+    }
+
     // Wait for the poll loop to terminate when the state is set to OFF.
     pthread_join(hci_poll_thread_id, NULL);
 
@@ -168,6 +176,10 @@ int mp_bluetooth_hci_uart_set_baudrate(uint32_t baudrate) {
 int mp_bluetooth_hci_uart_readchar(void) {
     // DEBUG_printf("mp_bluetooth_hci_uart_readchar\n");
 
+    if (uart_fd == -1) {
+        return -1;
+    }
+
     uint8_t c;
     ssize_t bytes_read = read(uart_fd, &c, 1);
 
@@ -184,6 +196,10 @@ int mp_bluetooth_hci_uart_readchar(void) {
 int mp_bluetooth_hci_uart_write(const uint8_t *buf, size_t len) {
     // DEBUG_printf("mp_bluetooth_hci_uart_write\n");
 
+    if (uart_fd == -1) {
+        return 0;
+    }
+
     #if DEBUG_HCI_DUMP
     printf("[% 8ld] TX: %02x", mp_hal_ticks_ms(), buf[0]);
     for (size_t i = 1; i < len; ++i) {