Which is the best microcomputer if its most important feature is...

A C166 can work that. You must life with it's pipeline.

Perhaps others too.

What do you want? Just a programmable delay line, 16-bits width?

- Henry

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"Don Lancaster" schrieb im Newsbeitrag news: snipped-for-privacy@mid.individual.net...

ADSP-218x. 0-cycle do loop iteration with two-cycle startup (CNTR= and the do, itself), single cycle access to two separate memory spaces while doing an ALU operation at the same time, fast cycle times are easy (I currently use 25ns cycles, but can be clocked faster), boots out of 8-bit eprom.

Of course, context is everything and I'm pretty sure this has to go with your PWM controller replacement idea (magic stuff.) If you are looking for in-line code to insert that is simply a 1-8191 cycle delay loop, then the ADSP-218x won't get you there. 3-8191, would be easy though:

cntr= ar; do x until ce; x: nop;

However, because of instruction packing, it's likely you could embed the loop start up elsewhere saving a cycle, so 2-8192. Close. If you further were to pack one of the instructions that followed the loop into the nop there, it could appear to be a 1-8191 cycle loop then to the application (assuming you don't mind executing that instruction a few times over and over.)

It can do a 16-bit indexed read from data space, a 16-bit indexed read from code space, and an ALU OP in a single cycle, though. Might be handy for your ap.

It's not cheap and the darned thing takes external support you probably won't want to add.

The dsPIC, I read, includes a 0-overhead do loop, as well. It's more of your usual microcontroller thing with some nice DSP-like stuff, such as these do loop things. Have you looked at it for your needs?

Jon

Do it in a programmable logic device. Ask on comp.arch.fpga for advice on which device.

Give more details ....

-- Bill Sloman, Nijmegen (but in Sydney at the moment).

On Sat, 09 Dec 2006 16:47:29 -0700, Don Lancaster Gave us:

Use the cell processor. Superscaler... no problem.

That pretty much sums it up.

But you have great heaping bunches of delays, some very short, some very long that need accessed without "pinch points" caused by overhead.

With a PIC, you have to split a 12-bit delay value into two parts - a calculated one and a table lookup one.

I do have a 0-255 cycle delay with only 6 cycles of total overhead on the PIC. By a calculated jump into a whole page of RETLW's. But pinch points and programming complexity make zeroing out more than the first

36 harmonics or so of a sinewave tricky. Especially for very low amplitudes.

More at

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I agree with Bill. Using a relatively small (read: cheap) CPLD or FPGA, you can have about 1000 times more flexibility in creating custom timers than you'll ever get with a microcontroller, with the residual error in your harmonics being due to the fundamental clock frequency you choose and the phase noise of the oscillator.

Without any indication of how long your "cycles" are supposed to be, it is impossible to answer your question. For example, if your cycles are 1 us, then pretty much any micro running at 50 MHz would be fine. But if you want your cycles at 50 ns, or perhaps variable, it's a lot harder.

You can come a long way with double-buffered pwm signals (so that you can seemlessly move from one pulse to the next), which are available on many micros. You could still have issues when you have two small pulses after each other.

Someone else mentioned programable logic - that is likely to be the most flexible and reliable method, especially at higher speeds.

Another idea would be using DMA (if you are looking for small micros, try an msp430f16x, or a small ColdFire for higher speed, power and flexibility). If you can arrange for DMA to update a double-buffered pwm unit, you will get jitter-free and almost cpu-free updates. I don't have all the details in my head, but I would expect that with a ColdFire MCF5213, you'd be able to do this on four indpendant channels at once, with a resolution of 25 ns or 50 ns.

I cannot answer here without more details. As others suggest, going the FGPA/CPLD way is maybe simpler.

- Henry

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"D> > A C166 can work that. You must life with it's pipeline.

amplitudes.

amplitudes.

If the machine cycles are very short does it still have to be only 3 ?

Im using one of the dspic30f series and they run 30mips, (upto 120mhz internaly generated clock from pll, max 40mhz extrnl clock src) It has 16/32 bit timers, pwm (motor control) outputs with upto 60mhz edge granularity.

ive not used any of the other high performance mcu's but there are many, some even have an integral cpld !

For sine conversion I found a very simple algorithm with just 1 multiplication (square). not sure about the level of harmonics however, but is fine for motor control. its probably mostly within 255 bits of resolution. you can probably add more terms to get closer aproximation.

Colin =^.^=

dont know what difference a MAC makes, but its just this

sin = 3/4-x^2 +x where 0-90' coresponds to x -.5 to +.5

I found it on a newsgroup somewhere, under crude sine approximation. there were other variations with different optimisations for error.

Colin =^.^=

Hey, what's that about? I use a LUT.. is there a better way if you have a MAC?

Best regards, Spehro Pefhany

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Without a MAC (or at least a hardware multiplier), the speed probably won't be there for practical applications.

Thanks, I thought it might be more of an incremental calculation.

Best regards, Spehro Pefhany

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"Spehro Pefhany" schrieb im Newsbeitrag news: snipped-for-privacy@4ax.com...

You can use the Bresenham for circles too! All left is shifting values.

- Henry

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oh that sort of MAC, yes no hardware multiply is a real limitation. single cycle 16 bit multiply is good, wouldnt like to be without it, well maybe my central heating controller doesnt realy need it ....

Colin =^.^=

This sort of thing is very dependent on exactly what you are trying to do, and how you are trying to do it. For example, in my 3-phase motor control firmware from a few years ago I had to write some fairly tight assembly to get the calculations done fast enough for to generate good sine waves at a few hundred Hz. It's easier nowadays, but the minimum one cycle delay request sounds like you're going to have problems unless you change your overall approach. Perhaps, if you can guarantee that the time between transitions is high enough you could use interrupts and more than one 16-bit timer, plus some simple logic off-chip (like an ex-or gate).

In general, if you're doing delays using firmware to get the outputs to do what you want, rather than hardware, you're probably doing something wrong, except perhaps in the very simplest of applications.

Best regards, Spehro Pefhany

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Maybe I'm missing something; doesn't this just mean you want an integrated

16-bit counter/timer? Something like MC68HC908QY4 has two such counters. No real point in doing something in software if your micro has such a peripheral mapped to its I/O pins...