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Re: [Discuss-gnuradio] GNU Radio on Android

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] GNU Radio on Android
Date: Mon, 23 Mar 2015 13:43:12 -0400

On Sun, Mar 22, 2015 at 6:29 PM, Vijay Galbaransingh <address@hidden> wrote:
Hi guys,

Still stuck, but some relevant details have changed that may help answer my
question. So I'm trying to implement a sink block for gnuradio-android that
takes integers on its input (not chars as I had erroneously written before)
and stores the last 'length' items in a LIFO buffer; the buffer's contents
are written to an Android TextView object every time the block's work
function is called. Following is the constructor I have written in order to
pass this block the JNIEnv and jobject variables it needs in order to access
the methods of my TextView instance:

    stream_to_tv_sink_impl::stream_to_tv_sink_impl(JNIEnv *env, jobject jtv,
int length)
      : gr::sync_block("stream_to_tv_sink",
              gr::io_signature::make(1, 1, sizeof(int),
              gr::io_signature::make(0, 0, 0)),
      d_buffer = new string[length];
      for(int i = 0; i < length; i++) {
        d_buffer[i] = "0";
      d_output = "Nothing yet...";
      jclass d_cls = env->GetObjectClass(jtv);
      jmethodID d_mid = env->GetMethodID(d_cls, "setText",

And here is my work function:

    stream_to_tv_sink_impl::work(int noutput_items,
                          gr_vector_const_void_star &input_items,
                          gr_vector_void_star &output_items)
        const int *in = (const int *) input_items[0];

        // Update LIFO
        for(int i = d_length - 1; i > 0; i--) {
            d_buffer[i] = d_buffer[i-1];
        d_buffer[0] = to_string(in[0]);

        // Construct output string, newest >> oldest (left to right)
        d_output = d_buffer[0];
        for(int i = 1; i < d_length; i++) {
        d_output += " " + d_buffer[i];

        // Display output string -- Invoke setText method
        d_env->CallVoidMethod(d_jtv, d_mid,
d_env->NewStringUTF(d_output.c_str())); // Might need to do this j times for
j < noutput_items

        // Tell runtime system how many output items we produced.
        return noutput_items;

Where I am stuck is I cannot figure out how to come up with the appropriate
makefile (using cmake or otherwise) to build this block into a prebuilt
static library so that I may use it in my Android flowgraph, as shown for
example in the instructions for building GNU Radio for Android and GRAnd at
https://gnuradio.org/redmine/projects/gnuradio/wiki/GRAndBuild. I don't have
much experience tinkering with cmake but I've been looking over the cmake
files in GRAnd and the android fork of gnuradio and I can't figure out how
to properly link to the JNI library to build this thing -- or if statically
linking to JNI types and methods in this manner is even possible. If it
isn't, I'm open to suggestions for alternative methods of displaying the
flowgraph's end results in my Android app; at the moment my flowgraph
terminates in a file sink, and the app reads/displays a few entries from the
file, but this not a good solution for when the flowgraph is running for
more than 10 or 15 seconds.

Any advice appreciated,

Hi Vijay,

So at this point I think you might be the person with the second most experience with GNU Radio on Android and therefore the second most qualified to answer the question :)

I'm sitting in Android sessions at ELC right now, though, so I can't go into details really here. All I'll say is to look closer at gr-grand. Specifically, look at the float_array block that I wrote. It uses jfloatArray and JNIEnv in creating this block, very much like how you want to handle your block. I might suggest adding your block (using gr_modtool add in your checkout of gr-grand) directly to gr-grand and try and build it there, since that CMake handles the necessary includes/libs/etc that you need to get the linking to work. That might at least get you to a buildable block for your purposes. It might then help you understand what you need to do with your own OOT projects CMake files.


-----Original Message-----
From: discuss-gnuradio-bounces+vijayg=address@hidden
[mailto:discuss-gnuradio-bounces+vijayg=address@hidden] On Behalf Of Vijay
Sent: March-21-15 00:51
To: 'Tom Rondeau'
Cc: 'GNURadio Discussion List'
Subject: Re: [Discuss-gnuradio] GNU Radio on Android

Hi guys,

I am attempting to write an OOT module to be implemented on Android and am
finding myself out of my depth here.

As a first step I was able to make and execute my flowgraph on my android
device following the instructions on the wiki, using a file sink to store my
end result (demodulated string.)

Now I would like to create my own sink which takes char inputs and updates a
TextView object as they are ‘spat out’ by the flowgraph. I followed the
general instructions on the wiki for coding an OOT module/object, so
gr_modtool generated all the boiler plate code and I have modified it

Where I am hitting an issue is that I must pass JNIEnv* and jobject
arguments to my make (hence impl) functions in order to interact with the
TextView object in my work function… but when I try to build the module I
get the following error for example: “error: 'JNIEnv' has not been declared”,
and similarly for all the jobject, jclass, and jmethodID occurrences. It
would seem make doesn’t know how to find the JNI libraries (and I’m guessing
volk is missing too,) and I’m unsure how to tell it where to look. Any
thoughts? Or is there a smarter / less roundabout way altogether to display
my flowgraph output in my Android activity?


From: address@hidden [mailto:address@hidden] On Behalf Of Tom
Sent: March-19-15 07:36
To: Vijay Galbaransingh
Cc: GNURadio Discussion List
Subject: Re: [Discuss-gnuradio] GNU Radio on Android

On Thu, Mar 19, 2015 at 3:28 AM, Vijay Galbaransingh <address@hidden> wrote:

As you expected, disabling buffering on the file sink did not have any
effect. I have fixed the issue though by making two changes to
1) change scale_factor to 32768 (1/2^14 doesn't make sense, it causes
clipping because the volk conversion method divides by scale_factor.)
2) change buffer size (d_size) to 8k (2k was too small, tested 32/44.1/48kHz
on Nexus 4 and Nexus 7 2012 version.) Without this change the recorded audio
will be very choppy (dropped samples?)


Ah, ok, that makes sense. I think I was just playing around with those
parameters and must have checked them in at that state.

I'll make those updates to the repo.


From: address@hidden [mailto:address@hidden] On Behalf Of Tom
Sent: March-18-15 07:11
To: Vijay Galbaransingh
Cc: GNURadio Discussion List
Subject: Re: [Discuss-gnuradio] GNU Radio on Android

On Wed, Mar 18, 2015 at 1:46 AM, Vijay Galbaransingh <address@hidden> wrote:

What kind of sample rate / setup are you using for your opensl_source? I've
set up a flowgraph that is just an opensl_source (sampling at 48kHz)
connected to a file sink, and when I play back the file through GRC on my
desktop my audio is coming out pretty garbled, as if samples are being
dropped. I've also tried a couple other sampling rates (44.1kHz, 32kHz,
16kHz to name a few.) I'm using a Nexus 4 running Android 5.0.1. Pasted
below is some of my code.


Flowgraph code:
Java_com_example_grrecordmic_GrRecordMic_InitFlowgraph(JNIEnv* env, jobject
thiz, jstring jsinkfilename)
    int rate = 48000;
    const char *sinkfilename = env->GetStringUTFChars(jsinkfilename, 0);

    global_tb = gr::make_top_block("Record_Mic");

    gr::grand::opensl_source::sptr micSource =
    gr::blocks::file_sink::sptr fileSink =
gr::blocks::file_sink::make(sizeof(float), sinkfilename, false);

    global_tb->connect(micSource, 0, fileSink, 0);

    env->ReleaseStringUTFChars(jsinkfilename, sinkfilename);

I believe that I used either 32k and/or 44.1k. I was using a Nexus 7,
though, and the codec might play a significant role with this between the
two devices.

Perhaps try setting the file sink to unbuffered mode?


Frankly, I feel like this is unlikely to help, but it'll be interesting to
know what happens.


From: address@hidden [mailto:address@hidden] On Behalf Of Tom
Sent: March-17-15 07:37
To: Vijay Galbaransingh
Cc: GNURadio Discussion List
Subject: Re: [Discuss-gnuradio] GNU Radio on Android

On Tue, Mar 17, 2015 at 12:10 AM, Vijay Galbaransingh <address@hidden> wrote:
Thanks Tom, that sorted it out. My audio output is a bit choppy but no
matter – time to move on to some more complex flowgraphs in my Android app.

Thanks again,

Yes, the skipping in the audio output is a known bug, and  apparently known
to be difficult in Android. It's going to take some kind of double buffering
to fix it at this level. I did not experience any problems with the audio
source, though; I just saved it to a file, brought it back to my computer,
and played it there and it sounded fine.


From: address@hidden [mailto:address@hidden] On Behalf Of Tom
Sent: March-16-15 06:37
To: Vijay Galbaransingh
Cc: GNURadio Discussion List
Subject: Re: [Discuss-gnuradio] GNU Radio on Android

On Mon, Mar 16, 2015 at 3:28 AM, Vijay Galbaransingh <address@hidden> wrote:
Hi Tom,

I have been following your notes on the wiki in an attempt to build a test
app (a dial tone flowgraph.) I'm hitting a snag on the ndk-build step
though -- when I use your example Android.mk listing, the linker isn't
finding any of the static libraries we built (gnuradio, grand, boost, fftw.)
Instead I'm getting a pile of undefined reference errors.

I tried editing the example Android.mk file by adding the following before
the shared library build:

include $(CLEAR_VARS)
LOCAL_MODULE := grand_static_lib #for example
LOCAL_SRC_FILES := /opt/grandroid/lib/libgnuradio-grand.a

However I quickly realised that while there are only a few gnuradio
libraries to add this way, there are a ton of boost libraries... Is there a
smarter way to add all the prebuilt .a libraries at once? Or am I headed in
the wrong direction entirely?

Any tips appreciated,

Yep, you have to add all of the libraries into the Android.mk file. I've
updated the wiki:


You can go there and simply download GrAndroid.mk that does all of this for
you and include it in your Android.mk file. Just follow the instructions.

Hope that helps,


From: address@hidden [mailto:address@hidden] On Behalf Of Tom
Sent: March-13-15 14:41
To: Vijay Galbaransingh
Cc: GNURadio Discussion List
Subject: Re: [Discuss-gnuradio] GNU Radio on Android
On Fri, Mar 13, 2015 at 5:04 PM, Vijay Galbaransingh <address@hidden> wrote:

Has a patched version of GNU Radio which runs on Android been released?

I'm working on a project where I'm transmitting information over audio
from a desktop system to an Android device, and since setting up the
transmitter end with GNU Radio was such a snap I would love to leverage
the GNU Radio system to build the receiver as well.


Just yesterday, in fact:


I'll try to release some of my apps soon. One of them captures from the
audio device, even. It's not too hard since there's the gr-grand opensl
audio source block to talk to the audio system.


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