drv/bluetooth_stm32_cc2640: Work around scanning stopping.

See pybricks/support#1096

lib/pbio/drv/bluetooth/bluetooth_stm32_cc2640.c

@@ -954,6 +954,20 @@ void pbdrv_bluetooth_stop_broadcasting(void) {
 static PT_THREAD(observe_task(struct pt *pt, pbio_task_t *task)) {
     PT_BEGIN(pt);
 
+    // HACK: Always stop observing first so that this task always does a clean
+    // restart of observing. This clears the size limited buffer of discovered
+    // devices. Should be replaced by a generalized scan process that only
+    // restarts scanning when needed. https://github.com/pybricks/support/issues/1096
+    if (is_observing) {
+        PT_WAIT_WHILE(pt, write_xfer_size);
+        GAP_DeviceDiscoveryCancel();
+        PT_WAIT_UNTIL(pt, hci_command_status);
+        if (read_buf[8] == bleSUCCESS) {
+            PT_WAIT_UNTIL(pt, device_discovery_done);
+        }
+        is_observing = false;
+    }
+
     if (!is_observing) {
         PT_WAIT_WHILE(pt, write_xfer_size);
         GAP_DeviceDiscoveryRequest(GAP_DEVICE_DISCOVERY_MODE_NONDISCOVERABLE, 0, GAP_FILTER_POLICY_SCAN_ANY_CONNECT_ANY);

pybricks/common/pb_type_ble.c

@@ -429,6 +429,22 @@ STATIC mp_obj_t pb_module_ble_observe(mp_obj_t self_in, mp_obj_t channel_in) {
 
     // Have not received data yet or timed out.
     if (ch_data.rssi == INT8_MIN) {
+
+        // HACK: Work around observing eventually stopping on the CC2640 due to
+        // full buffer of discovered devices. Needs to be fixed at the driver
+        // level with a scan process that restarts automatically.
+        // See https://github.com/pybricks/support/issues/1096
+        #if PBDRV_CONFIG_BLUETOOTH_STM32_CC2640
+        static uint32_t time_restart = 0;
+        uint32_t time_now = mp_hal_ticks_ms();
+        if (time_now - time_restart > OBSERVED_DATA_TIMEOUT_MS) {
+            pbio_task_t task;
+            pbdrv_bluetooth_start_observing(&task, handle_observe_event);
+            pb_module_tools_pbio_task_do_blocking(&task, -1);
+            time_restart = time_now;
+        }
+        #endif
+
         return mp_const_none;
     }