Why is the GPS operation always blocked

Question

One of my projects needs to use NB and GPS functions at the same time. When testing, I found that even though NB network is not transmitting data, after I start GPS, I often receive messages that the operation is blocked. Why is that?

This is my code:

static void set_gps_enable(const bool enable)
{
	u8_t tmpbuf[128] = {0};
	
	if(enable == gps_control_is_enabled())
	{
		return;
	}

	if(enable)
	{
		at_cmd_write("AT+CFUN?", tmpbuf, sizeof(tmpbuf), NULL);
		LOG_INF("modem status:%s", tmpbuf);
		if(strcmp(tmpbuf, "+CFUN: 1") != 0)
		{
			if(at_cmd_write("AT+CFUN=1", NULL, 0, NULL) != 0)
			{
				LOG_INF("Can't turn on modem!");
				EnterIdleScreen();
				return;
			}
		}
		
		LOG_INF("Starting GPS");
		gps_control_start(K_NO_WAIT);
		gps_is_on = true;
		gps_start_time = k_uptime_get();
	}
	else
	{
		LOG_INF("Stopping GPS");
		gps_control_stop(K_NO_WAIT);
		gps_is_on = false;
		gps_fix_time = 0;
		gps_local_time = 0;
	}
}

static void gps_handler(struct device *dev, struct gps_event *evt)
{
	u8_t tmpbuf[128] = {0};
	
	switch (evt->type)
	{
	case GPS_EVT_SEARCH_STARTED:
		LOG_INF("GPS_EVT_SEARCH_STARTED\n");
		gps_control_set_active(true);
		break;
		
	case GPS_EVT_SEARCH_STOPPED:
		LOG_INF("GPS_EVT_SEARCH_STOPPED\n");
		gps_control_set_active(false);
		break;
		
	case GPS_EVT_SEARCH_TIMEOUT:
		LOG_INF("GPS_EVT_SEARCH_TIMEOUT\n");
		gps_control_set_active(false);
		break;
		
	case GPS_EVT_PVT:
		/* Don't spam logs */
		LOG_INF("GPS_EVT_PVT");
		
		if(test_gps_flag)
		{
			u8_t i,tracked;
			u8_t strbuf[256] = {0};

			memset(gps_test_info, 0x00, sizeof(gps_test_info));
			
			for(i=0;i<GPS_PVT_MAX_SV_COUNT;i++)
			{
				u8_t buf[128] = {0};
				
				if((evt->pvt.sv[i].sv > 0) && (evt->pvt.sv[i].sv < 32))
				{
					tracked++;
			
					sprintf(buf, "%02d|%02d;", evt->pvt.sv[i].sv, evt->pvt.sv[i].cn0/10);
					strcat(strbuf, buf);
				}
			}

			sprintf(gps_test_info, "%d,", tracked);
			strcat(gps_test_info, strbuf);
			gps_test_update_flag = true;
			
			//LOG_INF("%s\n",gps_test_info);
			//UpdataTestGPSInfo();
			//TestGPSShowInfor();
		}
		else
		{
			sprintf(tmpbuf, "Longitude:%f, Latitude:%f, Altitude:%f, Speed:%f, Heading:%f", 
								evt->pvt.longitude, 
								evt->pvt.latitude,
								evt->pvt.altitude,
								evt->pvt.speed,
								evt->pvt.heading);
			LOG_INF("%s",tmpbuf);
			
			LOG_INF("Date:       %02u-%02u-%02u", evt->pvt.datetime.year,
						       					  evt->pvt.datetime.month,
						       					  evt->pvt.datetime.day);
			LOG_INF("Time (UTC): %02u:%02u:%02u\n", evt->pvt.datetime.hour,
						       					  evt->pvt.datetime.minute,
						      					  evt->pvt.datetime.seconds);
		}
		break;
	
	case GPS_EVT_PVT_FIX:
		LOG_INF("GPS_EVT_PVT_FIX");

		if(test_gps_flag)
		{
			u8_t i,tracked;
			u8_t strbuf[256] = {0};

			memset(gps_test_info, 0x00, sizeof(gps_test_info));
			
			for(i=0;i<GPS_PVT_MAX_SV_COUNT;i++)
			{
				u8_t buf[256] = {0};
				
				if((evt->pvt.sv[i].sv > 0) && (evt->pvt.sv[i].sv < 32))
				{
					tracked++;
			
					sprintf(buf, "%02d|%02d;", evt->pvt.sv[i].sv, evt->pvt.sv[i].cn0/10);
					strcat(strbuf, buf);
				}
			}

			sprintf(gps_test_info, "%d,", tracked);
			strcat(gps_test_info, strbuf);
			strcat(gps_test_info, "\n");
			sprintf(strbuf, "Longitude:%f, Latitude:%f\n", evt->pvt.longitude, evt->pvt.latitude);
			strcat(gps_test_info, strbuf);
			sprintf(strbuf, "fix time:%d", gps_local_time/1000);
			strcat(gps_test_info, strbuf);
			gps_test_update_flag = true;
			
			//LOG_INF("%s\n",gps_test_info);
			//UpdataTestGPSInfo();
			//TestGPSShowInfor();
		}		
		else
		{
			sprintf(tmpbuf, "Longitude:%f, Latitude:%f", evt->pvt.longitude, evt->pvt.latitude);
			LOG_INF("%s\n",tmpbuf);
		
			memcpy(&gps_pvt_data, &(evt->pvt), sizeof(evt->pvt));
		}
		break;
		
	case GPS_EVT_NMEA:
		/* Don't spam logs */
		LOG_INF("GPS_EVT_NMEA\n");
		break;
		
	case GPS_EVT_NMEA_FIX:
		LOG_INF("GPS_EVT_NMEA_FIX");

		if(gps_fix_time == 0)
		{
			gps_fix_time = k_uptime_get();
			gps_local_time = gps_fix_time-gps_start_time;
		}
		
		if(!test_gps_flag)
		{
			LOG_INF("Position fix with NMEA data, fix time:%d", gps_local_time);
			LOG_INF("NMEA:%s\n", evt->nmea.buf);
		
			APP_Ask_GPS_off();

			if(k_timer_remaining_get(&app_wait_gps_timer) > 0)
				k_timer_stop(&app_wait_gps_timer);

			k_timer_start(&app_send_gps_timer, K_MSEC(1000), NULL);
		}
		break;
		
	case GPS_EVT_OPERATION_BLOCKED:
		LOG_INF("GPS_EVT_OPERATION_BLOCKED\n");
		break;
		
	case GPS_EVT_OPERATION_UNBLOCKED:
		LOG_INF("GPS_EVT_OPERATION_UNBLOCKED\n");
		break;
		
	case GPS_EVT_AGPS_DATA_NEEDED:
		LOG_INF("GPS_EVT_AGPS_DATA_NEEDED\n");
		k_work_submit_to_queue(app_work_q,
				       &send_agps_request_work);
		break;
		
	case GPS_EVT_ERROR:
		LOG_INF("GPS_EVT_ERROR\n");
		break;
		
	default:
		break;
	}
}

void GPS_init(struct k_work_q *work_q)
{
	app_work_q = work_q;

	k_work_init(&send_agps_request_work, send_agps_request);

	gps_control_init(app_work_q, gps_handler);
}