Driver to drive?

[Joerg]

Jamie wrote:

Nico Coesel wrote:

josephkk <joseph_barrett@sbcglobal.net> wrote:


On Sun, 03 Mar 2013 19:51:06 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:


Joerg wrote:


Jamie wrote:
=20

Joerg wrote:



Spehro Pefhany wrote:


Oh yeah, we had a bunch that came in kits best suited for starter
electronic people from a particular source that were packaging them.
.
Also, back then surplus centers were very popular and you could find
these chips there and more than likely they were seconds but they
made their way out there in equipment where they didn't belong..

These days things are laser trimmed and that isn't such an issue any=20
more.

With today's methods of fabbing chips, I would bet a chip like that=20
could be reproduce with a much better yield and precision.

Jamie

They were sweet chips for their time, but now they are up against DDS
chips with 14+ bit dacs for not all that much. They can't compete, =
except
in the hobbyist market which way too small.


Well, FM and sweep seems to be a problem

i have a DDS function generator that does all of that and it
does not have any problems?

So do I and it dopesn't have modulation problems. But these are too big
even if I'd remove the enclosure and power supply.

I think you'll find if you don't have a latency problem with the
serial link to the chip, you should be able to do all the FMing you
want..

The problem with the uC on these little boards is not the serial link.
Well, at least not if 100Hz sweeps suffice. The problem is that they are
too small to calculate the numbers on the fly and usually have to little
flash left to store them in a LUT. Plus that would be a major
time-consuming hack.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Nico Coesel]

"Michael A. Terrell" <mike.terrell@earthlink.net> wrote:

John Larkin wrote:

I think ADI has a DDS chip that sweeps.

Why is it that ADI is the only outfit that makes DDS chips? I asked
one of their guys, and he didn't know.

We mostly do DDS in FPGAs.

Here is a link to the demo software for the AD8950 that does sweep.
ftp://ftp.analog.com/pub/www/techSupport/designTools/evaluationBoards/downloads/AD9850_51_V2.41_Win2KXP.exe

I doubt that he can download it and get it to run, like so much other
software. I had it installed on another computer and it works. You can
use the parallel port to connect the demo board to the PC and see that
it works.

They have sample code for the 8051 processor

If its software then it is not a real sweep but a stepped sweep. If
you use that to test a resonator or a notch filter you might be in for
a nasty surprise.

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico@nctdevpuntnl (punt=.)
--------------------------------------------------------------

 

[Michael A. Terrell]

Nico Coesel wrote:

"Michael A. Terrell" ?mike.terrell@earthlink.net? wrote:

?
?John Larkin wrote:
??
?? I think ADI has a DDS chip that sweeps.
??
?? Why is it that ADI is the only outfit that makes DDS chips? I asked
?? one of their guys, and he didn't know.
??
?? We mostly do DDS in FPGAs.
?
? Here is a link to the demo software for the AD8950 that does sweep.
??ftp://ftp.analog.com/pub/www/techSupport/designTools/evaluationBoards/downloads/AD9850_51_V2.41_Win2KXP.exe?
?
? I doubt that he can download it and get it to run, like so much other
?software. I had it installed on another computer and it works. You can
?use the parallel port to connect the demo board to the PC and see that
?it works.
?
? They have sample code for the 8051 processor

If its software then it is not a real sweep but a stepped sweep. If
you use that to test a resonator or a notch filter you might be in for
a nasty surprise.

That depends on the step size. Do you think modern network analyzers
are all analog?

 

[Nico Coesel]

"Michael A. Terrell" <mike.terrell@earthlink.net> wrote:

Nico Coesel wrote:

"Michael A. Terrell" ?mike.terrell@earthlink.net? wrote:

?
?John Larkin wrote:
??
?? I think ADI has a DDS chip that sweeps.
??
?? Why is it that ADI is the only outfit that makes DDS chips? I asked
?? one of their guys, and he didn't know.
??
?? We mostly do DDS in FPGAs.
?
? Here is a link to the demo software for the AD8950 that does sweep.
??ftp://ftp.analog.com/pub/www/techSupport/designTools/evaluationBoards/downloads/AD9850_51_V2.41_Win2KXP.exe?
?
? I doubt that he can download it and get it to run, like so much other
?software. I had it installed on another computer and it works. You can
?use the parallel port to connect the demo board to the PC and see that
?it works.
?
? They have sample code for the 8051 processor

If its software then it is not a real sweep but a stepped sweep. If
you use that to test a resonator or a notch filter you might be in for
a nasty surprise.


That depends on the step size. Do you think modern network analyzers
are all analog?

No, but they won't use a dead slow 8051 either Probably some FPGA
or ASIC.

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico@nctdevpuntnl (punt=.)
--------------------------------------------------------------

 

On Thu, 07 Mar 2013 00:43:13 GMT, nico@puntnl.niks (Nico Coesel)
wrote:

"Michael A. Terrell" <mike.terrell@earthlink.net> wrote:


Nico Coesel wrote:

"Michael A. Terrell" ?mike.terrell@earthlink.net? wrote:

?
?John Larkin wrote:
??
?? I think ADI has a DDS chip that sweeps.
??
?? Why is it that ADI is the only outfit that makes DDS chips? I asked
?? one of their guys, and he didn't know.
??
?? We mostly do DDS in FPGAs.
?
? Here is a link to the demo software for the AD8950 that does sweep.
??ftp://ftp.analog.com/pub/www/techSupport/designTools/evaluationBoards/downloads/AD9850_51_V2.41_Win2KXP.exe?
?
? I doubt that he can download it and get it to run, like so much other
?software. I had it installed on another computer and it works. You can
?use the parallel port to connect the demo board to the PC and see that
?it works.
?
? They have sample code for the 8051 processor

If its software then it is not a real sweep but a stepped sweep. If
you use that to test a resonator or a notch filter you might be in for
a nasty surprise.


That depends on the step size. Do you think modern network analyzers
are all analog?

No, but they won't use a dead slow 8051 either Probably some FPGA
or ASIC.

You mean an 8051 doesn't have infinite MIPS? Really? You do know that
an FPGA won't be perfect either?

 

[Michael A. Terrell]

Nico Coesel wrote:

"Michael A. Terrell" ?mike.terrell@earthlink.net? wrote:

?
?Nico Coesel wrote:
??
?? "Michael A. Terrell" ?mike.terrell@earthlink.net? wrote:
??
?? ?
?? ?John Larkin wrote:
?? ??
?? ?? I think ADI has a DDS chip that sweeps.
?? ??
?? ?? Why is it that ADI is the only outfit that makes DDS chips? I asked
?? ?? one of their guys, and he didn't know.
?? ??
?? ?? We mostly do DDS in FPGAs.
?? ?
?? ? Here is a link to the demo software for the AD8950 that does sweep.
?? ??ftp://ftp.analog.com/pub/www/techSupport/designTools/evaluationBoards/downloads/AD9850_51_V2.41_Win2KXP.exe?
?? ?
?? ? I doubt that he can download it and get it to run, like so much other
?? ?software. I had it installed on another computer and it works. You can
?? ?use the parallel port to connect the demo board to the PC and see that
?? ?it works.
?? ?
?? ? They have sample code for the 8051 processor
??
?? If its software then it is not a real sweep but a stepped sweep. If
?? you use that to test a resonator or a notch filter you might be in for
?? a nasty surprise.
?
?
? That depends on the step size. Do you think modern network analyzers
?are all analog?

No, but they won't use a dead slow 8051 either Probably some FPGA
or ASIC.

No specification was given for a sweep time, was it?

 

[josephkk]

On Mon, 4 Mar 2013 05:04:52 -0800 (PST), "langwadt@fonz.dk"
<langwadt@fonz.dk> wrote:

On Mar 4, 1:05 pm, n...@puntnl.niks (Nico Coesel) wrote:
John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Sun, 03 Mar 2013 22:35:28 GMT, n...@puntnl.niks (Nico Coesel) wrote:

John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

On Sun, 03 Mar 2013 20:38:07 GMT, n...@puntnl.niks (Nico Coesel) wrote:

Spehro Pefhany <speffS...@interlogDOTyou.knowwhat> wrote:

On Sun, 03 Mar 2013 18:49:31 GMT, the renowned n...@puntnl.niks (Nico
Coesel) wrote:

John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

On Sun, 03 Mar 2013 09:48:31 -0800, Joerg <inva...@invalid.invalid> wrote:

Just use
floating point. The chip is probably fast enough to emulate. After all
its one sin() and some additions to get the output. Some fast float to
integer conversion magic and its all done.

LPC43xx should be fast enough- it's got hardware floating point.

Floats don't help implementing the DDS core; they actually make it harder.

How come? IMHO generating a sine wave is a matter of output=sin(angle)
* amplitude. Angle is incremented by a step which depends on the
sample rate and frequency. From memory: Say your samplerate is 10kHz
and your output frequency is 105.3Hz then the size of each increment
is (2pi / 10kHz) * 105.3Hz radians. That is very easy to program.
Ofcourse it will need some tweaks to make it fast but the basics are
simple.

DDS uses a long (typically around 48 bits) integer phase accumulator which
conveniently overflows every 2pi radians with no additional code. The top N bits
(say, 10 or 12) are mapped through a sine table and drives the DAC. It's very
simple, just a few lines of code. You'd need double floats, overflow tests, some
sort of sine algorithm, and a float-to-fix conversion for the DAC. That would
require hardware floats, and probably woundn't work as well as the integer
version.

If you assume emulated floating point is infinitely slow but usually
it isn't. I have used emulated floating point in a signal processing
application on ARM before and I know it does have its advantages.


using the usual fixed point phase accumulator and then doing sin()
in float makes sense

but doing the phase accumutation in floats I'm not so sure about,
forever doing an accumulation modulo 2*pi sounds iffy

with fixed point it is exact since 2^n is defined to be 2*pi

BAMS. It has been around for over 50 years. (Fraction portion) MSB is
180 degrees and so forth. It is not all that well known though.

?-)

 

[josephkk]

On Mon, 04 Mar 2013 16:42:08 -0500, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

On Mon, 04 Mar 2013 06:54:32 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

I made some crude measurements on a 120MHz STM32F2, emulated floating
point and gcc:

Double Precision:
0.415us / 49.852 cycles /multiply
0.378us / 45.403 cycles /add
2.414us / 289.702 cycles /divide

Single Precision:
0.194us / 23.350 cycles /multiply
0.250us / 30.052 cycles /add
0.610us / 73.202 cycles / divide

Pretty respectable I thought.

Yes, but not transcendental calcs.

As compared to 1 cycle for add/sub/shift/mul on an ARM.

STM32F2 is an ARM Cortex M3.

There's no reason to use any floats in a DDS sinewave generator.

No, but it might make calculating the frequencies during a sweep a bit
easier.

I can even do that in fixed point. Select a reference frequency, say 100
Hz, then scale for frequency at beginning of sweep, and sweep step size
(may be negative for some cases), then each time you update the phase
register calculate the new value by adding step to current phase/step
value. loop until at stop frequency, reset phase step value to start and
go again.

If everything is fast enough you can even do high futility FM stereo
modulation at MHz carrier frequencies with an MP3 source. But at more
than 8 bits to the DAC you are looking at 200 MB/s, enough to choke a
single PCIe lane.

I'd be interested in how long a sin(x) or tan(x) (probably about the
same) takes for non-trivial angles. Or ln(x)/exp(x).

 

[Michael A. Terrell]

josephkk wrote:

On Mon, 04 Mar 2013 16:42:08 -0500, Spehro Pefhany
?speffSNIP@interlogDOTyou.knowwhat? wrote:

?On Mon, 04 Mar 2013 06:54:32 -0800, John Larkin
??jjlarkin@highNOTlandTHIStechnologyPART.com? wrote:
?
???I made some crude measurements on a 120MHz STM32F2, emulated floating
???point and gcc:
???
??? Double Precision:
??? 0.415us / 49.852 cycles /multiply
??? 0.378us / 45.403 cycles /add
??? 2.414us / 289.702 cycles /divide
???
??? Single Precision:
??? 0.194us / 23.350 cycles /multiply
??? 0.250us / 30.052 cycles /add
??? 0.610us / 73.202 cycles / divide
???
???Pretty respectable I thought.
?
?Yes, but not transcendental calcs.
?
??As compared to 1 cycle for add/sub/shift/mul on an ARM.
?
?STM32F2 is an ARM Cortex M3.
?
??There's no reason to use any floats in a DDS sinewave generator.
?
?No, but it might make calculating the frequencies during a sweep a bit
?easier.

I can even do that in fixed point. Select a reference frequency, say 100
Hz, then scale for frequency at beginning of sweep, and sweep step size
(may be negative for some cases), then each time you update the phase
register calculate the new value by adding step to current phase/step
value. loop until at stop frequency, reset phase step value to start and
go again.

If everything is fast enough you can even do high futility FM stereo
modulation at MHz carrier frequencies with an MP3 source. But at more
than 8 bits to the DAC you are looking at 200 MB/s, enough to choke a
single PCIe lane.
?
?I'd be interested in how long a sin(x) or tan(x) (probably about the
?same) takes for non-trivial angles. Or ln(x)/exp(x).

ADI has an ap note on generating FM Stereo via DDS, along with some
code. I saw it about a year ago.

 

[josephkk]

On Wed, 06 Mar 2013 14:48:39 -0800, Joerg <invalid@invalid.invalid> wrote:

i have a DDS function generator that does all of that and it
does not have any problems?


So do I and it dopesn't have modulation problems. But these are too big
even if I'd remove the enclosure and power supply.


I think you'll find if you don't have a latency problem with the
serial link to the chip, you should be able to do all the FMing you
want..


The problem with the uC on these little boards is not the serial link.
Well, at least not if 100Hz sweeps suffice. The problem is that they are
too small to calculate the numbers on the fly and usually have to little
flash left to store them in a LUT. Plus that would be a major
time-consuming hack.

If i could get you to stop and listen i could show you haw to do the
operating side in very little code space, no lookup table, fixed point
math without divides. The user interface or system interface is another
matter though.

?-)

 

[josephkk]

On Wed, 06 Mar 2013 07:24:48 -0800, Joerg <invalid@invalid.invalid> wrote:

josephkk wrote:
On Sat, 02 Mar 2013 12:37:10 -0800, Joerg <invalid@invalid.invalid> wrote:

Hi Folks,

Long story short, none of the DDS modules I've found so far has the
ability to be sweeped or FM-modulated. This one has a signal input
terminal block "SIN" but I received a response from the manufacturer
that it connects to nowhere, it has no function:

http://imall.iteadstudio.com/tools-and-equipment/im120723003.html

What I need in my case is DC-100Hz of sweep or FM bandwidth. Operating
frequency under 10kHz and sweep range up to 2kHz. Of course I can whip
up an analog solution but it won't be as precise and most of all not
really programmable.

Is there anything better? Cost is not a big issue but should be somewhat
small and a display would be nice.

So use the Armstrong method.


What, erythropoietin? Some kind of growth hormone?

See:

http://en.wikipedia.org/wiki/Edwin_Howard_Armstrong

http://en.wikipedia.org/wiki/Armstrong_phase_modulator

 

[Joerg]

josephkk wrote:

On Wed, 06 Mar 2013 14:48:39 -0800, Joerg <invalid@invalid.invalid> wrote:

i have a DDS function generator that does all of that and it
does not have any problems?

So do I and it dopesn't have modulation problems. But these are too big
even if I'd remove the enclosure and power supply.


I think you'll find if you don't have a latency problem with the
serial link to the chip, you should be able to do all the FMing you
want..

The problem with the uC on these little boards is not the serial link.
Well, at least not if 100Hz sweeps suffice. The problem is that they are
too small to calculate the numbers on the fly and usually have to little
flash left to store them in a LUT. Plus that would be a major
time-consuming hack.

If i could get you to stop and listen i could show you haw to do the
operating side in very little code space, no lookup table, fixed point
math without divides. The user interface or system interface is another
matter though.

I am sure it can be done somehow. But it's not a slam dunk because the
little uC in there is already running an LCD and other things. One could
do some interrupt shuffling and all that. But ... I've now resorted to
the old analog method. It's my home turf and there's just too many other
tasks at hand to let one like this balloon into its own sizeable project.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

josephkk wrote:

On Wed, 06 Mar 2013 07:24:48 -0800, Joerg <invalid@invalid.invalid> wrote:

josephkk wrote:
On Sat, 02 Mar 2013 12:37:10 -0800, Joerg <invalid@invalid.invalid> wrote:

Hi Folks,

Long story short, none of the DDS modules I've found so far has the
ability to be sweeped or FM-modulated. This one has a signal input
terminal block "SIN" but I received a response from the manufacturer
that it connects to nowhere, it has no function:

http://imall.iteadstudio.com/tools-and-equipment/im120723003.html

What I need in my case is DC-100Hz of sweep or FM bandwidth. Operating
frequency under 10kHz and sweep range up to 2kHz. Of course I can whip
up an analog solution but it won't be as precise and most of all not
really programmable.

Is there anything better? Cost is not a big issue but should be somewhat
small and a display would be nice.
So use the Armstrong method.

What, erythropoietin? Some kind of growth hormone?



See:

http://en.wikipedia.org/wiki/Edwin_Howard_Armstrong

http://en.wikipedia.org/wiki/Armstrong_phase_modulator

The way he died was very sad, I did not know that. Thanks for sharing.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Nico Coesel]

josephkk <joseph_barrett@sbcglobal.net> wrote:

On Mon, 04 Mar 2013 16:42:08 -0500, Spehro Pefhany
speffSNIP@interlogDOTyou.knowwhat> wrote:

On Mon, 04 Mar 2013 06:54:32 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

I made some crude measurements on a 120MHz STM32F2, emulated floating
point and gcc:

Double Precision:
0.415us / 49.852 cycles /multiply
0.378us / 45.403 cycles /add
2.414us / 289.702 cycles /divide

Single Precision:
0.194us / 23.350 cycles /multiply
0.250us / 30.052 cycles /add
0.610us / 73.202 cycles / divide

Pretty respectable I thought.

Yes, but not transcendental calcs.=20

As compared to 1 cycle for add/sub/shift/mul on an ARM.

STM32F2 is an ARM Cortex M3.=20

There's no reason to use any floats in a DDS sinewave generator.

No, but it might make calculating the frequencies during a sweep a bit
easier.=20

I can even do that in fixed point. Select a reference frequency, say 100
Hz, then scale for frequency at beginning of sweep, and sweep step size

Ofcourse but with floating point its a total no brainer so faster to
develop. In the end floating point is automatic fixed point without
having to think about where to put the decimal point for maximum
accuracy.

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico@nctdevpuntnl (punt=.)
--------------------------------------------------------------

 

[Jasen Betts]

On 2013-03-06, Nico Coesel <nico@puntnl.niks> wrote:

"Michael A. Terrell" <mike.terrell@earthlink.net> wrote:


John Larkin wrote:

I think ADI has a DDS chip that sweeps.

Why is it that ADI is the only outfit that makes DDS chips? I asked
one of their guys, and he didn't know.

We mostly do DDS in FPGAs.

Here is a link to the demo software for the AD8950 that does sweep.
ftp://ftp.analog.com/pub/www/techSupport/designTools/evaluationBoards/downloads/AD9850_51_V2.41_Win2KXP.exe

I doubt that he can download it and get it to run, like so much other
software. I had it installed on another computer and it works. You can
use the parallel port to connect the demo board to the PC and see that
it works.

They have sample code for the 8051 processor

If its software then it is not a real sweep but a stepped sweep. If
you use that to test a resonator or a notch filter you might be in for
a nasty surprise.

Not if the software runs fast enough and is done right.

You can microstep a DDS's frequency by jittering the phase accumulator
step size.

--
⚂⚃ 100% natural

--- news://freenews.netfront.net/ - complaints: news@netfront.net ---

 

[Nico Coesel]

Jasen Betts <jasen@xnet.co.nz> wrote:

On 2013-03-06, Nico Coesel <nico@puntnl.niks> wrote:
"Michael A. Terrell" <mike.terrell@earthlink.net> wrote:


John Larkin wrote:

I think ADI has a DDS chip that sweeps.

Why is it that ADI is the only outfit that makes DDS chips? I asked
one of their guys, and he didn't know.

We mostly do DDS in FPGAs.

Here is a link to the demo software for the AD8950 that does sweep.
ftp://ftp.analog.com/pub/www/techSupport/designTools/evaluationBoards/downloads/AD9850_51_V2.41_Win2KXP.exe

I doubt that he can download it and get it to run, like so much other
software. I had it installed on another computer and it works. You can
use the parallel port to connect the demo board to the PC and see that
it works.

They have sample code for the 8051 processor

If its software then it is not a real sweep but a stepped sweep. If
you use that to test a resonator or a notch filter you might be in for
a nasty surprise.


Not if the software runs fast enough and is done right.

Fast enough and done right usually don't go well with an 8051. In an
ideal sweep (or FM modulation) you'd have to recalculate the step size
for every sample.

You can microstep a DDS's frequency by jittering the phase accumulator
step size.

Somehow I have a feeling that will look funny on a spectrum analyzer.
My guess is that you'll see two distinct peaks instead of an
intermediate frequency.

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico@nctdevpuntnl (punt=.)
--------------------------------------------------------------

 

[nuny@bid.nes]

On Mar 8, 1:37 pm, Double-A <double...@hush.com> wrote:

"Phys.org) —In the strange world of quantum mechanics, the vacuum
state (sometimes referred to as the quantum vacuum, simply as the
vacuum) is a quantum system's lowest possible energy state. While not
containing physical particles, neither is it an empty void: Rather,
the quantum vacuum contains fluctuating electromagnetic waves and so-
called virtual particles, the latter being known to transition into
and out of existence. In addition, the vacuum state has zero-point
energy – the lowest quantized energy level of a quantum mechanical
system – that manifests itself as the static Casimir effect, an
attractive interaction between the opposite walls of an
electromagnetic cavity. Recently, scientists at Aalto University in
Finland and VTT Technical Research Centre of Finland demonstrated the
dynamical Casimir effect using a Josephson metamaterial embedded in a
microwave cavity. They showed that under certain conditions, real
photons are generated in pairs, and concluded that their creation was
consistent with quantum field theory predictions."

http://phys.org/news/2013-03-nihilo-dynamical-casimir-effect-metamate...

Is this not a parametric amplifier?


Mark L. Fergerson

 

[George Herold]

On Mar 7, 9:26 pm, josephkk <joseph_barr...@sbcglobal.net> wrote:

On Wed, 06 Mar 2013 07:24:48 -0800, Joerg <inva...@invalid.invalid> wrote:
josephkk wrote:
On Sat, 02 Mar 2013 12:37:10 -0800, Joerg <inva...@invalid.invalid> wrote:

Hi Folks,

Long story short, none of the DDS modules I've found so far has the
ability to be sweeped or FM-modulated. This one has a signal input
terminal block "SIN" but I received a response from the manufacturer
that it connects to nowhere, it has no function:

http://imall.iteadstudio.com/tools-and-equipment/im120723003.html

What I need in my case is DC-100Hz of sweep or FM bandwidth. Operating
frequency under 10kHz and sweep range up to 2kHz. Of course I can whip
up an analog solution but it won't be as precise and most of all not
really programmable.

Is there anything better? Cost is not a big issue but should be somewhat
small and a display would be nice.

So use the Armstrong method.

What, erythropoietin? Some kind of growth hormone?



See:

http://en.wikipedia.org/wiki/Edwin_Howard_Armstrong


http://en.wikipedia.org/wiki/Armstrong_phase_modulator

Cool, I've seen this phasor diagram that shows FM is just 90 deg phase
shifted AM. (but only at low amplitude) I never knew how to make it
work, 'in practice'.

George H.

- Hide quoted text -

- Show quoted text -

 

[josephkk]

On Fri, 08 Mar 2013 20:50:25 GMT, nico@puntnl.niks (Nico Coesel) wrote:

josephkk <joseph_barrett@sbcglobal.net> wrote:

On Mon, 04 Mar 2013 16:42:08 -0500, Spehro Pefhany
speffSNIP@interlogDOTyou.knowwhat> wrote:

On Mon, 04 Mar 2013 06:54:32 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

I made some crude measurements on a 120MHz STM32F2, emulated floating
point and gcc:

Double Precision:
0.415us / 49.852 cycles /multiply
0.378us / 45.403 cycles /add
2.414us / 289.702 cycles /divide

Single Precision:
0.194us / 23.350 cycles /multiply
0.250us / 30.052 cycles /add
0.610us / 73.202 cycles / divide

Pretty respectable I thought.

Yes, but not transcendental calcs.=20

As compared to 1 cycle for add/sub/shift/mul on an ARM.

STM32F2 is an ARM Cortex M3.=20

There's no reason to use any floats in a DDS sinewave generator.

No, but it might make calculating the frequencies during a sweep a bit
easier.=20

I can even do that in fixed point. Select a reference frequency, say 100
Hz, then scale for frequency at beginning of sweep, and sweep step size

Ofcourse but with floating point its a total no brainer so faster to
develop. In the end floating point is automatic fixed point without
having to think about where to put the decimal point for maximum
accuracy.

I understand where you are coming from. But the nature of this
application, as stated, is inherently fixed point with an obvious radix
placement. Why put up with FP overhead when you don't need to.

Different viewpoint for this case.

?-)

 

[Jasen Betts]

On 2013-03-08, Nico Coesel <nico@puntnl.niks> wrote:

Jasen Betts <jasen@xnet.co.nz> wrote:

On 2013-03-06, Nico Coesel <nico@puntnl.niks> wrote:

If its software then it is not a real sweep but a stepped sweep. If
you use that to test a resonator or a notch filter you might be in for
a nasty surprise.


Not if the software runs fast enough and is done right.

Fast enough and done right usually don't go well with an 8051. In an
ideal sweep (or FM modulation) you'd have to recalculate the step size
for every sample.

I understand that 8051 is the uC that everone that everyone loves to
hate, but the claim depends on the frequency you're running it all at.

You can microstep a DDS's frequency by jittering the phase accumulator
step size.

Somehow I have a feeling that will look funny on a spectrum analyzer.
My guess is that you'll see two distinct peaks instead of an
intermediate frequency.

You have to do it between each sample. It's the same effect you'd get
by adding more bits to the phase accumulator, but not widening eange
of phase bits used for output.

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