Vala DataInputStream.read_int32 in accelerometer message

[RANJAN]

On Sun, Oct 11, 2009 at 1:38 AM, MicVM <ssj2micvm at gmail.com> wrote:

>
> I am trying to build a vala library to access the accelerometers of the
> freerunner. I am using vala just to give it a try but I am experiencing
> strange problems and wanted to ask if some of you can give me some hints.
> When i read from the input interface of an accelerometer i get the
> following
> bytestream:
>
> b 3 d1 4a 42 ea d 0 0 0 0 0 0 0 0 0
> 1b 3 d1 4a 79 f e 0 3 0 1 0 6c 0 0 0
> 1b 3 d1 4a d7 f e 0 3 0 2 0 26 4 0 0
>
> that looks quite good to me. However, when I try to read the values in the
> message as integers i have a problem when reding the "value" field, i.e.
> the
> last 32 bit signed integer of the message. I get strange values around +300
> instead of +1062 for the Z value as in the last line of the above example.
> Also for X and Y the values are wrong. I read the stream with the following
> code snippet in vala (using GIO libs):
>
> var data_stream=new DataInputStream(file_stream);
> data_stream.set_byte_order(DataStreamByteOrder.LITTLE_ENDIAN);
>
> //Skip time field, 8 bytes
> data_stream.skip(8,null);
>
> //Read eventtype
> eventtype=data_stream.read_uint16(null);
> while(eventtype!=0)
> {
>        if((eventtype==3)||(eventtype==2))
>        {
>                code=data_stream.read_uint16(null);
>                if(code==0)
>                {
>                        x_value=data_stream.read_int32(null);
>
>                }
>                if(code==1)
>                {
>                        y_value=data_stream.read_int32(null);
>                }
>                if(code==2)
>                {
>                        z_value=data_stream.read_int32(null);
>                }
>
> ....
>
> I think somewhere I am doing a major mistake because the decoding of the
> int32 is a basic functionality that does not work in my case. The funny
> thing is that decoding of uint16 is done correctly such that eventtype and
> code are read correctly. Any help is appreciate :)
> --
> View this message in context:
> http://n2.nabble.com/Vala-DataInputStream-read-int32-in-accelerometer-message-tp3801000p3801000.html
> Sent from the Openmoko Devel mailing list archive at Nabble.com.
>
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What is the maximum frequency at which you are able to read the
accelerometer values?
Are you able to sample the values properly?
Are the reading in X and Y changing smoothly?

Here is a test that I conducted:
http://www.youtube.com/watch?v=Bdads8XAYcE&feature=fvsr

Sriranjan
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