My team has been struggling with a pretty strange issue while using the WinRT/C++ APIs for Windows to connect to both a MIDI port and receive BLE notifications through a proprietary service on the same device.
The WinRT/C++ library itself is really nice and provides easy and modern C++ interfaces to access the managed Windows runtime classes.
I've pushed a sample repo to Github where we've replicated the issue with a minimal example.
The repo's readme goes over the problem in detail, but I'll post the relevant bits here for completeness.
The sample program is performing roughly these steps:
Check for available MIDI devices using a DeviceWatcher.
Check for available Bluetooth LE devices using another instance of a DeviceWatcher.
Match discovered MIDI and BluetoothLE devices on their ContainerId property (see DeviceInfo for details). This is the method JUCE employs in the native WinRT code for their library, and works as expected.
Open the MIDI port and attach a handler to the MessageReceived event (see the code).
This causes the system to create a connection to the Bluetooth LE device. The program detects this state change, creates a BluetoothLEDevice, we perform GATT service discovery and attach a handler to the ValueChanged event for the characteristic we're interested in notifications from (see the code).
The program then counts how many MIDI messages are received on each port and how many BLE notifications are received from the corresponding device.
The behaviour we notice is that data from the most recently connected device streams just fine, while the throughput for the others is severly limited. We are at quite a standstill regarding this issue, and are not sure where the problem may lie.
We are at quite a standstill here. I'd be more willing to accept it if all the devices would exhibit this behaviour, but that's not the case. Is there any reason that creating both a MidiInPort and an BluetoothLEDevice from the same peripheral should cause this issue?
A BLE radio can only receive or send at any given time. And therefore only communicate with one device at any given time. It uses a scheduler to allocate radio time for every device when you have many devices. That way a second connection can "interrupt" a connection event from another device, decreasing the throughput for that device. See https://infocenter.nordicsemi.com/topic/sds_s132/SDS/s1xx/multilink_scheduling/central_connection_timing.html
Related
I want to build something with Raspberry Pi Zero and write in Go,
I never tried bluetooth before and my goal is;
Sending a dynamic packet which it will change every second, an iOS app will expand this message and with a button, client will send a message back without a connection.
Is Bluetooth Advertising what I am looking for and do you know any GoLang library for it? Where should I start?
There are quite a lot of parts to your question. If you want to be connection-less then the BLE roles are Broadcaster (beacon) and Observer (scanner). There are a number of "standard" beacon formats out there. They are summarized nicely on this cheat sheet
Of course you can create your own format as these are using either the Service Data or Manufacturing Data in a BLE advertisement.
On Linux (Raspberry Pi) the official Bluetooth stack is BlueZ which documents the API's available at: https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/doc
If you want to be connection-less then each device is going to have to change it's role regularly. This requires a bit of careful thought on how long each is listening and broadcasting as you don't want them always talking at the same time and listening at the same time.
You might find the following article of interest to get you started with BLE and Go Lang:
https://towardsdatascience.com/spelunking-bluetooth-le-with-go-c2cff65a7aca
I am building an Android App to control power outlets with a smartphone. The app features an Android Wear app so people can control their lights right from their wrist.
When the user wants to control a light I send a String action via the MessageApi from the smartwatch to the smartphone, which receives this action in a WearableListenerService and sends the appropriate network signal to the power outlet/gateway in an AsyncTask.
This works fine as long as the phone has not been in idle for too long. However if the phone is still on the table for too long and doze kicks in Wear actions do execute very slow or sometimes not at all. I guess this is in part intended behavior however it is not practical in my case as the user cant wait that long for his lights to turn on if he wants to enter a dark room.
I am aware that doze completely cuts the networking for everything except FCM/GCM if you are not on the doze whitelist. But even when my app is on this whitelist and the networking part works actions can take a long time to execute on the phone.
So my specific question is:
Whats the recommended way to handle this scenario, where an action from a wearable device needs to be done via network on the connected smartphone which is in doze mode?
Is there a way to exit doze for a quick amount of time to execute calculations triggered by the wearable companion app faster?
I know the AlarmManager has a new method that works even in doze mode, but will this fix the processing delay too? Firing an alarm after receiving a MessageEvent from MessagApi seems like a workaround to me.
Or maybe is an AsyncTask just the wrong way to handle background networking and thats where the delay comes from?
Actually, there are a few options that you can do to handle Doze's effects as given in Adapting your app to Doze. You may want to consider the following options:
If your app requires a persistent connection to the network to receive messages, you should use Google Cloud Messaging (GCM) if possible.
GCM is optimized to work with Doze and App Standby idle modes by means of high-priority GCM messages. GCM high-priority messages let you reliably wake your app to access the network, even if the user’s device is in Doze or the app is in App Standby mode.
To help with scheduling alarms, Android 6.0 (API level 23) introduces two new AlarmManager methods: setAndAllowWhileIdle() and setExactAndAllowWhileIdle(). With these methods, you can set alarms that will fire even if the device is in Doze.
However, please note that with these methods, neither setAndAllowWhileIdle() nor setExactAndAllowWhileIdle() can fire alarms more than once per 9 minutes, per app.
Please try going through Optimizing for Doze and App Standby for a more detailed information or discussion.
In addition to these given documentations, the same options in handling Doze were also given and discussed in Diving into Doze Mode for Developers which might also help.
I have been using Windows APIs for NFC communication. I am successful in getting and sending NFC messages from Windows PC, using a local console app. However, I want the communication to be done using a Windows service. Here is what I have:
A C# plugin (DLL), which makes the API calls.
C++/CLI Wrapper that allows unmanaged C++ code, to use the above plugin.
A C++ plugin, that the service will load (this is a requirement, it has to be a plugin)
If I load the C++ plugin into a local console app, and run, it can catch all NFC events (NFC device arrives in proximity, departs from proximity, can read and write to it). But, when I use the same plugin with a service, it is not able to catch those events. I can clearly hear the ping sound that comes when an NFC device comes close to Windows PC, however, none of the event handlers are called (For device arrival, device departure, read or write).
I also tried impersonation thinking that perhaps the context of who calls the method might result in blocking of the events. I could impersonate local user on the service, but the results were the same, no events could be identified.
Is there a reason why I cannot see any NFC events from a service, where as a local console app can get all of them? Again, I am able to hear the ping sound signifying that NFC device is close to Windows PC, but there is no handler getting called for it, suggesting there is blockage of something. Any ideas of what is going on?
Appreciate your time guys!
I'm planing to start some sms based application and currently in feasibility study part. In my application client have to sms their problem to the server and we have to analyse the problem and take reasonable action. Also We have to find the tentative location through which tower they have been connected. I have seen about silent sms feature but not understand. Is any body have experience on how to detect location of sms creator (not in android or iphone). Please help me on determining whether it is possible or not to find the location. If possible then how?
In short this is not possible.
an SMS message weather in PDU mode or text mode does not carry the information to match the source location to the message in any way shape or form.
With reference to the article you linked to in your opening post, I'm sorry to say that there's so much B$$l S$$t in that post that I can smell it from here.
In all the years Iv'e worked with GSM systems, both as a network maintenance engineer and later as a developer writing software to use these systems, not once have I heard of anything such as an 'LMU' or an 'E-OTD' in fact the only acronym that article really got correct was 'BTS' oh and the bit on passing the data over the signalling channel.
As for the silent SMS, well that part actually is true. The special type of SMS they refer to is actually called a Ping-SMS and it exists for exactly the same reason that a regular PING on a TCP/IP network exists, and that's to see if the remote system is alive and responding.
What it's NOT used for is the purpose outlined in the article, and that's for criminal gangs to send it to your phone and find out where you are.
For one, the ONLY people that can correctly send these messages are the telephone operator themselves. That's not to say that it's impossible to send one from a consumer device by directly programming a PDU if you have the necessary equipment and know how. You could for instance pull this stunt off using a normal GSM modem, a batch of AT commands and some serious bit twiddling.
However, since this message would by it's very nature have to go through your operators SMSC and most operators filter out anything from a subscriber connection that's not deemed regular consumer traffic, then there's a high chance this would fail.
You could if you had an account, also send this message using a web sms provider that allowed you to directly construct binary messages, but again they are likely to filter out anything not deemed consumer grade messages.
Finally, if you where to manage to send an SMS to a target device, the target device would not reply with anything anywhere near a chunk of location based info, cell tower, GPS or otherwise. The reason the SMS operators (and ultimately the law enforcement agencies know this info) is because EVERY handset that's attached to the GSM network MUST register itself in the operators MSC (Mobile switching centre), this registration (Known as ratching up) is required by the network so it can track what channels are in use by which device on which towers so that it knows where to send paging and signalling info.
Because of the way the PING SMS works it causes the destination device to re-register itself, usually forcing the MSC to do a location update on the handset which causes a re-registration.
Even then, all you get in the MSC is an identifier of the cell site the device is attached too, so unless you have a database in the organisation of all cell sites along with their exact lat/long co-ordinates, it's really not going to help you all that much.
As for the triangulation aspect, well for that to work you'd need to know at least 2 other transmitters that the device in question can see, and what's more you'd need that device to report that info back to someone inside the network.
Since typically it's only the Ril (Radio interface layer) on the device that actually keeps track of which transmitters it can see, and since the AT commands for many consumer grade GSM modems have the ability to query this information disabled, then it's often not easy to get that info without actually hacking the firmware in the device in question.
How does Google do it? well quite easy, they actually have commercial agreements with network providers that pass the details of registered towers to their back-end infrastructure, in the apps themselves, they have ways of getting the 'BSS List' and sending that list back to Google HQ, where it's cross referenced with the data from the network operator, and the info they have in their own very large transmitter database and finally all this is mashed together with some insane maths to get an approximate location.
Some GSM Modems and some Mobile phone handsets do have the required AT commands enabled to allow you to get this information easy, and if you can then match that information to your own database you can locate the handset your running from, but being able to send a special SMS to another device and get location info back is just a pipe dream nothing more, something like this is only going to work if your target device is already running some custom software that you can control, and if your device is running software that someone else is controlling, then you have bigger problems to worry about.
I'm writing a windows utility that communicates to a a USB Device. The driver is a custom driver, supplied by Analog Devices (the manufacturer of the controller chip used in the device).
I've adapted one of their example Windows apps for communcicating with the device. Communication is done via named pipes, and can be synchronous or asynchronous. The problem I've found during testing is that calls to the WriteFile api function can sometimes fail to return if the device is switched off during a write (the device has a hard power switch). The same thing is observed using async or sync calls - I see no timeout happening when using aysnc.
After this has happened, I need to restart my app, as the thread dealing with USB communications is hung.
Is there a way I can prevent the WriteFile from failing to return in this case?
Thanks
Tom Davies.
You can cancel IO operations using CancelSynchronousIo and CancelIoEx. You could do this if you detect that your comm thread is unexpectedly blocking during writes.
Possible deal breakers:
Available only in Windows Vista and newer
Driver has to support cancellation