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| Using ESP32 and Neo-7N for precise frequency measurement |
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| ogden:
--- Quote from: mark03 on September 15, 2018, 12:24:49 am ---What's the motivation for direct clocking from XO? --- End quote --- PLLs of stm32 have inherent phase noise, but ADC clock phase noise creates ADC aperture jitter. --- Quote ---Is jitter that much of an issue at these sample rates? --- End quote --- Depends on what for you is issue. 300ps jitter (PLL spec of most most stm32's) means that 11-bit ENOB is not good anymore for input signals above ~200KHz (!) frequency. Most 1MSPS applications will be fine, but even stm32f1xx interleaved mode become kinda useless, not to mention 5MSPS ADCs' of higher-end chips and their interleaved modes. https://www.maximintegrated.com/en/design/tools/calculators/general-engineering/jitter.cfm |
| ogden:
--- Quote from: tggzzz on September 14, 2018, 09:32:51 pm ---Whats the time resolution with which you can know when inputs occurred? --- End quote --- High resolution timer: 217ps As stm32 have ARM core, you can get answers to other questions yourself. --- Quote ---I very much doubt it gets anywhere vaguely close to the xCORE processors! --- End quote --- So what? It does not automagically mean that at every timing application you shall throw xCORE! :palm: Please don't even try to start stm32 vs xCORE flames. It is obvious that xCORE is faster :-DD At least you said so. What about availability, chip & devtools & debug interface price, learning curve, community support? |
| mark03:
--- Quote from: ogden on September 15, 2018, 04:33:50 am --- --- Quote ---Is jitter that much of an issue at these sample rates? --- End quote --- Depends on what for you is issue. 300ps jitter (PLL spec of most most stm32's) means that 11-bit ENOB is not good anymore for input signals above ~200KHz (!) frequency. Most 1MSPS applications will be fine, but even stm32f1xx interleaved mode become kinda useless, not to mention 5MSPS ADCs' of higher-end chips and their interleaved modes. https://www.maximintegrated.com/en/design/tools/calculators/general-engineering/jitter.cfm --- End quote --- Hmmm. STM32L4 claims one order of magnitude better than that (about 30 ps). Maybe the older lines are worse? In any case, I've always thought the high sample rates were primarily there so you can throw away samples in exchange for more bits. Hence the usefulness of the built-in CIC. I guess there are applications where you can actually process 1 MSPS data directly, but they must be rather limited? |
| tggzzz:
--- Quote from: ogden on September 15, 2018, 04:51:55 am --- --- Quote from: tggzzz on September 14, 2018, 09:32:51 pm ---Whats the time resolution with which you can know when inputs occurred? --- End quote --- High resolution timer: 217ps --- End quote --- I suspect that figure conceals important practical limitations. Can you "schedule", say, 10 different outputs to change at 217ps intervals, or "measure" that 10 different inputs changed at 217ps intervals? For obvious reasons you can't have software involved in that, it has to be done by a separate hardware in each i/o pin/port. The xCORE devices have such hardware, so you can schedule/measure any/all i/o at 4ns intervals. --- Quote ---As stm32 have ARM core, you can get answers to other questions yourself. --- Quote ---I very much doubt it gets anywhere vaguely close to the xCORE processors! --- End quote --- So what? It does not automagically mean that at every timing application you shall throw xCORE! :palm: --- End quote --- Please don't invent strawman arguments. --- Quote ---Please don't even try to start stm32 vs xCORE flames. It is obvious that xCORE is faster :-DD At least you said so. What about availability, chip & devtools & debug interface price, learning curve, community support? --- End quote --- The company, XMOS, has been shipping processors for at least 10 years, and continues to gather more investment from a wide range of well-known companies. It is based on sound software concepts from the 70s (now being incorporated into languages like Rust and Go), processors/languages from the 80s, and modern semiconductor capabilities. An excellent long-term pedigree. Buy it at DigiKey, as per previous URL. Dev tools are free, excellent, based on eclipse, and extend eclipse's standard functionality to exploit the hardware+software ecosystem's unique advantages. I've seen many "new revolutionary" ics/software/etc over the decades; almost all fail to live up to expectations! I first used xCORE/xC to "kick the tyres" and see if it lived up to its promises - it did far exceeded my expectations. It was extraordinarily easy to get programs that just worked as expected. In particular the peripheral i/o is remarkably simple because the hardware and software are co-designed by people With A Clue. As for an RTOS? Who needs one - those functions are done in hardware. As for community support. Yes it exists - but I haven't needed to use it because I didn't encounter any unexpected behaviour! And that's remarkable. Basically, it just worked as stated on the tin. |
| iMo:
fyi: STM32F334 only - "high res timers" - 217ps resolution available for all operating modes, variable duty cycle, variable frequency, transition mode,… Those high res timers are used for fine adjustments of pwm in critical applications. It does not relate to the "precise freq measurments".. Otherwise the PLL's of all MCUs are a crap, so I would not use them for something called "precise frequency measurement".. ;) |
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