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IQMath sin table has 512 values or 1024 values??

Prakash Kumar Thulasi Kumar
Expert 2015 points

Hi Guys,

I am using TMS32F28027 MCU. I wrote a simple code to test the sin table and then printed its values to a text file using Breakpoint method. Actually I am calling till 512, but the text file has 1024 values. I have attached the text file with this post.

My questions:

Array size of sin table, is it 512 or 1024?

Even if it has 1024 values, why is it saving all 1024 values to the text file? Because I am calling till 512 only(pls see CODE below).

The first three values stored in the text file are always garbage value(pls see text file), how to overcome this?

CODE:

void main(void)
{
   int  y = 0;   _iq x = _IQ(0);
    for(y = 0; y<512; y++){
        x = _IQ30toIQ(IQsinTable[y]);
    }
}

Fullscreen data.txt Download 
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  • 0
    TI__Guru**** 171094 points
    Prakash,

    The file format you are saving is a .dat file format, where the first line shows a few details about the file itself. To learn about what these numbers mean, open CCS help and search for "data file formats".

    From that point and on, each value is duplicated. I don't exactly know what is the size of the type _iq (16 or 32 bits), but to me this indicates the values on the sin table are 16 bits but your code is duplicating these values when storing them to a 32-bit variable. Or perhaps the values are full 32-bits but the code is corrupting them.

    To validate this code, try to save the data directly from the sin table address using the Memory save option and compare the two.

    Hope this helps,
    Rafael
  • 0 in reply to desouza
    Expert 2015 points
    Hi desouza,

    Thanks for your reply. _iq is of type long. Global IQ is 15 and the IQsinTable returns IQ30 values. This duplication effect occurs only when writing the values of IQsinTable to a txt file.
    x = _IQ30toIQ(IQsinTable[y]);
    Instead of &x, I gave IQsinTable in the start address field, but all the values are 0. Any other suggestions?