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TI DSP's Q float system

R

Robert

Jan 1, 1970
0
Hi all,

I am new to TI DSP. And I am using 320C55X series. I found their float
system use something like Q13.3, 13 bits integer and 3 bits fraction.

I search in TI's document(instruction set) and did not find any thing
about it.

Is there any instruction related to it and is it just software
implemented?

Any suggestions will be appreciated!
Best regards,
Davy
 
T

Tim Wescott

Jan 1, 1970
0
Robert said:
Hi all,

I am new to TI DSP. And I am using 320C55X series. I found their float
system use something like Q13.3, 13 bits integer and 3 bits fraction.

I search in TI's document(instruction set) and did not find any thing
about it.

Is there any instruction related to it and is it just software
implemented?

Any suggestions will be appreciated!
Best regards,
Davy
1. It's not floating point, it's fixed.

2. This would be a good question for comp.dsp.

3. It's mostly implemented as a convention, although there's a C
library that supports it. In assembly you get to set the radix any darn
way you want. The MAC instruction has a built-in shift, but I don't
know if it's used for these operations (that's tool chain specific).

4. If you can't find stuff in TI's DSP documentation join the club.
It's usually there, but sometimes it seems like it'd be quicker to build
your own chip starting from sand than to find it in their documentation.
 
S

steve

Jan 1, 1970
0
I think you are referring to TI's fixed point math library

http://focus.ti.com/docs/toolsw/folders/print/sprc087.html

is sort of a bridge between writing pure fixed point code with all the
headaches and using a pure software floating point library (slow but
easy to write).

Its about 4-5 times slower then pure fixed point (if I remember
correctly), but much faster then floating point emulation (20-100
slower then fixed point depending on the algorithm your implementing).
It still requires to figure out what the dynamic range is for your
signals and choose an appropriate "Q" factor.

Just my opinion but for me, its the worse of both worlds, slow and
still have to worry about dynamic ranges, but others think is the best
of both worlds, fast and little scaling worries.
 
R

Robert

Jan 1, 1970
0
Hi Steve,

I just want to use the image lib provide by TI C55x. And it use "Q", as
you said it is a math lib, I see.

Thanks!
Davy
 
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