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I think that you can get a minimal OS to run its tasks always quicker than a certain length of time and be able to count on your task to run at some frequency. Maybe that can be tuned with a tunable OS?

Also, I've programmed and run a whole lot to run on single-tasking (sometimes with TSR's) DOS and there's a lot to be said about your program having the system to itself. Like being able to run a business on 10 Mz and slower 8080 to 8088 CPU's, or 16 Mz 80286 with terminals... at all.
DOS is an OS.

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DOS is an OS.
DOS is a "program loader."
Not that that's a bad thing, nor does it disqualify it from being an "operating system."
If RPi is toggling a pin at 21MHz, that's without the linux operating system being involved.
Talking to IO in fast system is always slower than the internal cycle time.  Switching a pin at (relatively) high power at the edge of your circuitry and with a potentially significant load capacitance is "difficult."
(You also don't want to look too closely at how slow that RAM memory access is, on cache misses.)

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IIRC it takes an 8080 2 to 4 cycles to do most anything and way more to do some things.

On a 6502 the same happens in 1 cycle. ... or 2.


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DOS is an OS.
DOS is a "program loader."
Not that that's a bad thing, nor does it disqualify it from being an "operating system."
If RPi is toggling a pin at 21MHz, that's without the linux operating system being involved.
Talking to IO in fast system is always slower than the internal cycle time.  Switching a pin at (relatively) high power at the edge of your circuitry and with a potentially significant load capacitance is "difficult."
(You also don't want to look too closely at how slow that RAM memory access is, on cache misses.)

OK, that is something I suspected and hoped was not true, but thanks for the information.  On the Atmel chips you can get a square wave at clock divided by four, 21Mhz on a 700Mhz system is clock divided by thirty three.  I was hoping that the Raspberry Pi was a cheap and simple route to working with higher throughput chips, like high-speed ADCs with parallel interfaces (e.g. 8 bit 100Msps), but I can see that was a pipe dream.  smiley-sad  I'd rather write code than figure out how to get a FPGA to work.
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Vexatious Sampler

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high-speed ADCs with parallel interfaces
You might be able to connect those via the memory interface, or via some sort of DMA scheme.  But you probably can't get 100MHz; that's only 10ns for each byte, which is down near the propagation delay for individual logic-gate chips...
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What you do with the data is going to make a difference. Hope it's not high-res face or voice recognition.

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What you do with the data is going to make a difference. Hope it's not high-res face or voice recognition.

Nah, I had some dumbass idea to make a simple oscilloscope out of it.   Just something to look at dv/dt.

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high-speed ADCs with parallel interfaces
You might be able to connect those via the memory interface, or via some sort of DMA scheme.  But you probably can't get 100MHz; that's only 10ns for each byte, which is down near the propagation delay for individual logic-gate chips...

In the end if I can't get a microcontroller that can keep up I am thinking of a pure logic solution that just plows it into static RAM once the trigger voltage is hit, maybe with a CPLD or an FPGA, and then have the microcontroller read it out of memory and analyze it.  I have to figure all that out, it is outside of my skill level right now but probably not for very long.
« Last Edit: October 03, 2012, 11:26:55 pm by JoeN » Logged

Vexatious Sampler

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Are you making square waves or reading waveforms?


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Are you making square waves or reading waveforms?

You talkin' to ME?  smiley  I will assume so...

I would be reading, not writing, if I was looking to pull data off an ADC.  I was just using the data the guy posted about square waves being the likely upper limit for reading bits off the GPIO pins as well as writing to them.  I am not sure if that is true, but I am going with that for the time being.  My Raspberry Pi arrived from Newark today so I will have to get an image ready for it and see what it can really do.
« Last Edit: October 04, 2012, 01:10:35 pm by JoeN » Logged

Vexatious Sampler

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It may be possible to read at 100MHz for long enough to take a useful sample, but getting a 100MHz ADC working well will be a challenge I think, you won't be able to play with is on a breadboard at that speed.

I played with a similar idea a while back, I eventually decided to use hardware for the sampling into external RAM and a fast uC for triggering etc.

That said some processors have a camera interface (I think that's what it's called), most notably the PICs. AFAIK this is designed to read a parallel port directly and DMA the results into memory. That may be a good option.

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Rob Gray aka the GRAYnomad www.robgray.com

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today i get my 68332 cpu
Isn't that a bit old?  Shouldn't you be looking at ColdFire microcontrollers instead?  (ok, I haven't checked whether there's a Coldfire+TPU version.  There ought to be; 68332 is getting ancient!)

I have a 68331 development board around somewhere.  It's left over from an actual 68331 development project that I was pretty deeply involved in (the cisco-500 Terminal Server!)
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I bought 3 HC-SR04 Ultrasonic range finders from AZtronics for$5 each!!!

They are really accurate, easy to use, but you can see the side lobes coming into play.

I figured for $5 a piece I'd give them a try.

Because the output is digital there is a lot of "information" that you'll miss, such as the "quality" of the echo.

The way I'd normally do it gives me an idea of what the echo came from, just like watching an old school "fish finder" on a boat.

The other surprise I got was my free sample from Coridium!
One of these!

http://www.coridium.us/prod-specs1.html

I was thinking of making a shield for it!

Overkill?

Hell yeah!

a 50Mhz ARM sitting on an Arduino seems like a good idea!  smiley-cool
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Being as the LPC1114 is the only DIP ARM around I'd say it will be a popular chip. You can get in a TSSOP as well and that will fit inside the DIP footprint IIRC. So you could make a board that allowed for PHT and SMD, one for hobbyists/protoyping and the other for production.

Coridium have loaded a BASIC interpreter, maybe Picaxe had better look out. I'd post about this on their forum but they are very touchy about posts regarding other products and they get summarily deleted.
 
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Rob Gray aka the GRAYnomad www.robgray.com

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It's not a Basic interpreter!

The HackaDay article was really misleading, it runs compiled code.

HackaDay seem to be going down hill at a rate of knots!

The "just plug an FTDI cable in and pretend it's 1986" was a crock.

In the comments section the bloke from Coridium address's a few of the claims the writer made.

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Yes I see, it's a compiler.

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Rob
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