nRF52 direct access to EasyDMA

RE: nRF52 direct access to EasyDMA

Shlomo Zippel — Thu, 12 Nov 2015 14:17:49 GMT

Ah, that makes sense. Now I'm looking at the correct docs and I see "Decoder with EasyDMA" which is exactly what I need! infocenter.nordicsemi.com/.../Chunk1670748135.html

RE: nRF52 direct access to EasyDMA

RK — Thu, 12 Nov 2015 14:09:14 GMT

No the PWM LIBRARY which you reference has nothing to do with the PWM PERIPHERAL on the nRF52. The library uses timers and PPIs, the peripheral is a standalone hardware peripheral. That's why I couldn't find the limitation in the manual, there isn't one listed. There's a few vague mentions of PWM minimum period but it's not specified. I think it may be quite possible to run at the speed you like and generate the kind of waveform you're looking for ... IF the PWM peripheral works on whatever version of the chip you have.

RE: nRF52 direct access to EasyDMA

RK — Thu, 12 Nov 2015 14:02:31 GMT

Yes you can have from-memory waveforms, you can even change the top counter limit to change the frequency as you go although you wouldn't need to. That documentation is very dense however and since the preview chip didn't have PWM working, I've not looked at it in detail. 5us is quite long isn't it, that's 320 clock cycles, or 80 16MHz cycles if you're thinking in terms of that peripheral clock. I'd have though easyDMA would be able to load and update the registers faster than that. You want 1.25us however and that really is quite short.

If I had a chip with working PWM, I'd be tempted to try it and see how fast I could make it go reliably.

RE: nRF52 direct access to EasyDMA

RK — Thu, 12 Nov 2015 13:43:57 GMT

yah I just found 0.6.3 and have replaced my tatty 0.6 PDF version, newer version seems a bit more complete too.

RE: nRF52 direct access to EasyDMA

Shlomo Zippel — Thu, 12 Nov 2015 13:41:17 GMT

infocenter.nordicsemi.com/index.jsp

RE: nRF52 direct access to EasyDMA

Shlomo Zippel — Thu, 12 Nov 2015 13:41:04 GMT

I didn't realize PWM can generate a from-memory waveform, I thought it only has a period and duty cycle and is timer driven. How would I generate a waveform from EasyDMA memory? That would be amazing! :)

RE: nRF52 direct access to EasyDMA

RK — Thu, 12 Nov 2015 13:40:34 GMT

you must have a more up-to-date manual than I do as mine doesn't have the 200kHz, '200 kHz' or the word glitches in it anywhere. Let me go hunt for a newer one.

RE: nRF52 direct access to EasyDMA

Shlomo Zippel — Thu, 12 Nov 2015 13:38:20 GMT

From PWM docs: "PWM frequency is limited to 200 kHz (5 microseconds period). Exceeding this value might introduce glitches in the output signal."

RE: nRF52 direct access to EasyDMA

RK — Thu, 12 Nov 2015 13:23:34 GMT

Yes if you use EasyDMA via any hardware peripheral you are limited to the speeds it supports and the output formats it's designed to produce.

Does the PWM module really only support up to 200kHz for from-memory waveforms? I haven't read the whole thing, I've started a few times and decided to get back to it when I really need it as it's rather dense. Certainly you can run it much faster, but I haven't seen the limitations on arbitrary waveforms.

RE: nRF52 direct access to EasyDMA

Shlomo Zippel — Thu, 12 Nov 2015 13:09:47 GMT

Yes, I meant hardware peripherals. So if I use EasyDMA via SPIM I am limited to the frequencies that SPI supports, right?

RE: nRF52 direct access to EasyDMA

RK — Thu, 12 Nov 2015 13:07:57 GMT

There are no underlying EasyDMA registers, there are various peripherals which use EasyDMA and you access EasyDMA via their registers for that peripheral instance. By 'higher level libraries' did you actually mean 'hardware peripherals', because they're rather different concepts?

No you cannot use EasyDMA outside of a hardware peripheral.

RE: nRF52 direct access to EasyDMA

Shlomo Zippel — Thu, 12 Nov 2015 13:04:07 GMT

Can you please point me to the right location in the docs or register name? All I can find are specific uses of it for SPI / UART etc but not the underlying EasyDMA registers

RE: nRF52 direct access to EasyDMA

RK — Thu, 12 Nov 2015 13:00:10 GMT

Of course you can - it's all documented in the manual - you just set up the registers and let it roll.

Note that EasyDMA has quite a few anomalies on the preview chips, so ensure you're using hardware resources which are actually working.