LAUNCHXL-F28027F: Interpreting how a long format value appears as floating point (Q-Value(24))

asha singh1

Part Number: LAUNCHXL-F28027F
Other Parts Discussed in Thread: TMS320F28027F

Hi,

I have LaunchPad XL Tms320F28027F plus Boostxl-Drv8305.

Running system via the ccsv7 debugger and observing live data thru the "Expressions" window.
I wanted to understand the value "qMotorVars.IqRef_A" which is long in the code but in the Expressions widow shows "0.0 (Q-Value(24))"
I am printing the qMotorVars.IqRef_A via terraterm and see the values in decimal as 529253, 201553, 448743, 529253, 410453
How does this convert to a floating point like 0.00211xxxxxx etc ??

I have gone thru the "C28x IQmath Library" as well as processors.wiki.ti.com/.../IQmath_Library_for_C28x
But I am not clear how "529253" can be converted to a floating point number.

I am attaching the "Expressions" window output.LongFormatToQValue(24).docx

Any help/suggestion would be very much appreciated.
Thank you,
Asha

over 8 years ago

0 Yanming Luo over 8 years ago

TI__Guru** 115420 points

It's not a real float, it's IQmath uses the internal hardware of the C28x in the most efficient way to operate with 32bit fixed-point numbers. If the project used IQ24 format, it's equal to 529253/2^24, it's a long value, not a float vlaue, just display as float in watch window which don't take any more cycles. More detail information, you can refer to IQmath library user guide.

0 asha singh1 over 8 years ago in reply to Yanming Luo

Expert 1030 points

Thank you,
This is the answer I was looking for,
Thanks,
Asha

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LAUNCHXL-F28027F: Interpreting how a long format value appears as floating point (Q-Value(24))