Run NimBLE stack on the mgos task

We still need another task to monitor the queue but processing happens
on the mgos task itself, so we don't have to do complex task switching
for callbacks later.

src/esp32/esp32_bt.c

@@ -24,6 +24,7 @@
 
 #include "common/mg_str.h"
 
+#include "mgos_freertos.h"
 #include "mgos_hal.h"
 #include "mgos_net.h"
 #include "mgos_sys_config.h"
@@ -36,6 +37,8 @@
 #include "services/gap/ble_svc_gap.h"
 
 uint8_t own_addr_type;
+static TaskHandle_t s_host_task_handle;
+static volatile bool s_mgos_handler_pending = false;
 
 void mgos_bt_addr_to_esp32(const struct mgos_bt_addr *in, ble_addr_t *out) {
   switch (in->type) {
@@ -184,19 +187,57 @@ static void esp32_bt_synced(void) {
   mgos_bt_gap_set_adv_enable(mgos_sys_config_get_bt_adv_enable());
 }
 
-static void ble_host_task(void *param) {
-  LOG(LL_DEBUG, ("BLE task %s", "running"));
-  nimble_port_run();
-  nimble_port_freertos_deinit();
-  LOG(LL_DEBUG, ("BLE task %s", "exiting"));
+// Handler callback that executes host events on the mgos task.
+// For efficiency, we process multiple events at a time.
+static void esp32_bt_mgos_handler(void *arg) {
+  int nevs = 1;
+  struct ble_npl_event *ev, **ep, *evs[20] = {arg};
+  struct ble_npl_eventq *q = nimble_port_get_dflt_eventq();
+  // Try to get more events from the queue.
+  for (ep = evs + 1; nevs < ARRAY_SIZE(evs); nevs++) {
+    ev = ble_npl_eventq_get(q, 0 /* no wait */);
+    if (ev == NULL) break;
+    *ep++ = ev;
+  }
+  // Release the other task.
+  s_mgos_handler_pending = false;
+  // Process the events.
+  for (ep = evs; nevs > 0; ep++, nevs--) {
+    ble_npl_event_run(*ep);
+  }
+}
+
+static void esp32_bt_host_task(void *param) {
+  if (param == NULL) {  // This is the dummy task.
+    nimble_port_freertos_deinit();
+    return;
+  }
+  struct ble_npl_event *ev;
+  struct ble_npl_eventq *q = nimble_port_get_dflt_eventq();
+  while (1) {
+    ev = ble_npl_eventq_get(q, BLE_NPL_TIME_FOREVER);
+    s_mgos_handler_pending = true;
+    while (!mgos_invoke_cb(esp32_bt_mgos_handler, ev, false /* from_isr */)) {
+    }
+    // Wait for the mgos task callback to run and process the event.
+    while (s_mgos_handler_pending) {
+      taskYIELD();
+    }
+  }
 }
 
 static void esp32_bt_start(void *arg) {
-  LOG(LL_DEBUG, ("BLE task %s", "starting"));
+  LOG(LL_DEBUG, ("BLE task %s %d", "starting", MGOS_TASK_PRIORITY));
   if (!esp32_bt_gatts_init()) {
     LOG(LL_ERROR, ("%s init failed", "GATTS"));
   }
-  nimble_port_freertos_init(ble_host_task);
+  // This creates the high-pri LL task and a host task.
+  // We don't use the latter because its priority is too high.
+  nimble_port_freertos_init(esp32_bt_host_task);
+  // Instead we create our own here with priority below the main mgos task.
+  xTaskCreatePinnedToCore(esp32_bt_host_task, "ble", 1024, (void *) 1,
+                          MGOS_TASK_PRIORITY - 1, &s_host_task_handle,
+                          NIMBLE_CORE);
   ble_hs_sched_start();
   (void) arg;
 }