/ bias on
Have a look at the TS101S or TS201S (ADI's TigerSharcs). These have a
dual floating point core that can also run fixed (32,16,8) in parallel
instead of floats, i.e. you get both. TS101s are at 300 MHz, and TS201S
are 500-600 MHz (but very new).
/ bias off
Nick ELLIOTT wrote:
>
> My application is going to need a bit of fixed point, a bit of floating
> point calculations.
> Any advice as to whether a 720MHz fixed point processor (TI C64x) executing
> floating point libraries, can compete with a 225MHz floating point processor
> (TI C67x) ?
>
> Regards
> Nick
Reply by Tim Olson●June 30, 20032003-06-30
| --
| "Jerry Avins" <jya@ieee.org> wrote in message
| news:3EFA72BA.97D6C72@ieee.org...
| > Nick ELLIOTT wrote:
| > >
| > > My application is going to need a bit of fixed point, a bit of floating
| > > point calculations.
| > > Any advice as to whether a 720MHz fixed point processor (TI C64x)
| executing
| > > floating point libraries, can compete with a 225MHz floating point
| processor
| > > (TI C67x) ?
| > >
| > > Regards
| > > Nick
| >
| > That has to depend on how bib that "bit" of fp is compared to the FP.
"Nick ELLIOTT" <elliotts-in-nz@xtra.co.nz> replied:
| say 50:50
It probably won't perform anywhere near what you need, then. Software
FP requires breaking up the data into components (sign, exponent,
significand), significand alignment, operation, renormalization, and
repacking the components. For FP addition (the hardest), it is probably
50 cycles or so. To get a very rough idea we can use Amdahl's law:
sw fp performance = 1/(1/2 + 20/2) = ~9%
So with a 50:50 mix of FP and integer, a 720MHz software-only solution
is only going to perform about like a 65MHz hardware FP solution.
--
-- Tim Olson
Reply by Nick ELLIOTT●June 30, 20032003-06-30
say 50:50
--
"Jerry Avins" <jya@ieee.org> wrote in message
news:3EFA72BA.97D6C72@ieee.org...
> Nick ELLIOTT wrote:
> >
> > My application is going to need a bit of fixed point, a bit of floating
> > point calculations.
> > Any advice as to whether a 720MHz fixed point processor (TI C64x)
executing
> > floating point libraries, can compete with a 225MHz floating point
processor
> > (TI C67x) ?
> >
> > Regards
> > Nick
>
> That has to depend on how bib that "bit" of fp is compared to the FP.
>
> Jerry
> --
> Engineering is the art of making what you want from things you can get.
> �����������������������������������������������������������������������
Reply by Keith Larson●June 26, 20032003-06-26
Hi Nick
If you are doing floating point for setting up coefficients, FP
emulation is not that big of a pain. On the other hand, if FP is needed
within the main DSP loop (each data sample)... ouch!
This results from the fact that to do the FP emulation (on a fix pt
machine) the exponent and mantissa math operations are performed
seperately, typicaly on structures that are kept in memory and or
registers (if you have a gazillion of them to burn). Also, since the
ADDF and MPYF operations are now seperate entities, there is no such
thing as a MPF||ADDF parallel 'MAC' operation. A multitude of ouches!
Incidentally, this is also true when you are trying to do 32 bit math on
a 16 bit processor. Here you will find the overhead to be large for a
dual MAC architecture since the setup and register usage can be large
not to mention the deep pipelines. These types of architectures are
really suited for chunking through vast arrays of data that are setup in
advance.
Finally, since (most) Floating Point CPU's also have fixed point
capability, it is much easier to go in the other direction as needed.
The downside is that processors like the one I support (the VC33) want
to only work with 32 bit data. 16 bit (and shorter) data is not an
automatic type.
The bottom line is that you need to wade through the BS and pick the
processor that best fits the job and these days more importantly,
budget. And dont be fooled into thinking budget is simply the cost of
the DSP!
Best regards,
Keith Larson
============================
Nick ELLIOTT wrote:
> My application is going to need a bit of fixed point, a bit of floating
> point calculations.
> Any advice as to whether a 720MHz fixed point processor (TI C64x) executing
> floating point libraries, can compete with a 225MHz floating point processor
> (TI C67x) ?
>
> Regards
> Nick
+------------------------------------------+
|Keith Larson |
|Member Group Technical Staff |
|Texas Instruments Incorporated |
| |
| 281-274-3288 |
| k-larson2@ti.com |
|------------------------------------------+
| TMS320C3x/C4x/VC33 Applications |
| |
| TMS320VC33 |
| The lowest cost and lowest power |
| floating point DSP on the planet! |
| 500uw/Mflop |
+------------------------------------------+
Reply by Jerry Avins●June 26, 20032003-06-26
Nick ELLIOTT wrote:
>
> My application is going to need a bit of fixed point, a bit of floating
> point calculations.
> Any advice as to whether a 720MHz fixed point processor (TI C64x) executing
> floating point libraries, can compete with a 225MHz floating point processor
> (TI C67x) ?
>
> Regards
> Nick
That has to depend on how big that "bit" of fp is compared to the FP.
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Leon Heller●June 26, 20032003-06-26
"Nick ELLIOTT" <elliotts-in-nz@xtra.co.nz> wrote in message
news:gLrKa.50775$JA5.897875@news.xtra.co.nz...
> My application is going to need a bit of fixed point, a bit of floating
> point calculations.
> Any advice as to whether a 720MHz fixed point processor (TI C64x)
executing
> floating point libraries, can compete with a 225MHz floating point
processor
> (TI C67x) ?
You can take the floating-point calculations you require and
compile/assemble them for both processors. Simulating the resultant code for
both DSPs should give you an accurate comparison. I've done this sort of
thing for ADI DSPs, when I had two alternative FP techniques.
Leon
--
Leon Heller, G1HSM
leon_heller@hotmail.com
http://www.geocities.com/leon_heller
Reply by Jerry Avins●June 26, 20032003-06-26
Nick ELLIOTT wrote:
>
> My application is going to need a bit of fixed point, a bit of floating
> point calculations.
> Any advice as to whether a 720MHz fixed point processor (TI C64x) executing
> floating point libraries, can compete with a 225MHz floating point processor
> (TI C67x) ?
>
> Regards
> Nick
That has to depend on how bib that "bit" of fp is compared to the FP.
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Nick ELLIOTT●June 25, 20032003-06-25
My application is going to need a bit of fixed point, a bit of floating
point calculations.
Any advice as to whether a 720MHz fixed point processor (TI C64x) executing
floating point libraries, can compete with a 225MHz floating point processor
(TI C67x) ?
Regards
Nick