Outputting a PWM signal and it's inverse thru gpio pins

[refer_pin]

Hello,

I have two questions:

How do I access the gpio pins of nrf52840 dk? what example program from nrf5 sdk can I use as example?

Is there a simpler example program to output a pwm signal of example like 400kHz and it's inverse in the pins?I'm looking at the PWM driver example of nrf5 sdk and it's a really big leap for someone like me who's use to programming via Arduino IDE

[Karl Ylvisaker]

Hello,

How do I access the gpio pins of nrf52840 dk? what example program from nrf5 sdk can I use as example?

The description of the application above sounds very similar to the functionality demonstrated in our PWM Library example from the SDK. I highly recommend checking out this example, to see how you may go about setting up two inverted PWM's using the PWM library provided in the SDK.

pwm signal of example like 400kHz

Unfortunately, the pwm library instances are limited to 200 kHz. If you need 400 kHz, you will need to make use of the PWM peripheral. You could see how this can be used in the PWM driver example - however, this example might seem a little intense for someone who's most used to Arduino development. The example contains multiple demons, which in turn makes it seem daunting to familiarize with.

To make things easier, you could instead have a look at the project I have included below, which is made for the nRF52840 DK. This project is the same as the one referenced by my colleague Torbjørn in this ticket. It showcases a much simpler approach to setting up the PWM peripheral, with a much less complex output. Once you get the hang of this example and how it works, you can begin looking at modifying it for your application needs.
Mind you that this example uses the legacy nrf_drv driver, but in never SDK's this is using the nrfx driver behind the scenes through forwarding macros.
2627.pwm_driver_simple.zip
You should have a look at the nrfx_pwm API Reference when you start modifying the example.

I'm looking at the PWM driver example of nrf5 sdk and it's a really big leap for someone like me who's use to programming via Arduino IDE

No worries at all - we've all been new to this at some point! :) 
Please do not hesitate to ask, if you should encounter any issues or questions.

Best regards,
Karl

[refer_pin]

Karl Ylvisaker said:

You could see how this can be used in the PWM driver example

Oh so I should use the pwm driver example rather than the pwm library when going to output 400kHz?

Karl Ylvisaker said:

The example contains multiple demons, which in turn makes it seem daunting to familiarize with

By any chance you can provide me some resource I could read on or guidance so I could learn to handle these demons? I'm really new in this embedded programming stuff

Karl Ylvisaker said:

This project is the same as the one referenced by my colleague Torbjørn in this ticket

Are you referring to the zip file you attached?

[refer_pin]

Karl Ylvisaker said:

How do I access the gpio pins of nrf52840 dk?

 I meant was how do I access for example pin P0.06 on the board? I tried looking at the pwm_library example and all I can recognized being programmed are BSP_LED_0 and BSP_LED_1?

[refer_pin]

Karl Ylvisaker said:

In your case, you will rather need to use the PWM peripheral - which gives you much more options to configure the waveform generation.

Sure, I'll study pwm_driver example for outputting 400kHz

Karl Ylvisaker said:

Before looking at the PWM driver demos I would recommend that you read through the PWM peripheral documentation

Yes, I think I'm somehow in a way grasping how pwm is generated here but like a really vague understanding to begin with

Karl Ylvisaker said:

Is there anything else in particular you would like know more about when it comes to embedded programming?

I think from my part I understand the C programming part. What comes confusing for me are the terminologies behind the explanation. It's honestly my first time dealing with terms such as prescalers, registers, and countertops and while I think I can grasp it, I would somehow slip as I read further along the document. This is something I am not good at right now and I was wondering if you could provide guidance on what possible resource I can look up to better understand these terminologies or what topic/subject are they tackled in.

Karl Ylvisaker said:

one of the best examples to start looking at when you come directly from Arduino is probably the TIMER peripheral example.

Yup, I think it's a really simple program to start studying to get familiar with. I'm a bit confuse where I can read up on "_WFI()" and "NRF_SUCCESS"? It's my first time seeing them in C

[Karl Ylvisaker]

Thank you for your patience.

refer_pin said:

I meant was how do I access for example pin P0.06 on the board?

You may access P0.06 with the NRF_GPIO_PIN_MAP(0,6) function call.
Please also know that P0.06 is usually used for the UART TX PIN in all the SDK examples.

To see how this is all done in the nRF52840 DK file, you oculd take a look at the pca10056.h file located in SDK\components\boards\pca10056.h

Best regards,
Karl

[Karl Ylvisaker]

refer_pin said:

Yes, I think I'm somehow in a way grasping how pwm is generated here but like a really vague understanding to begin with

Great! It might seem like a ton of things to familiarize with, but it gets easier fast.

refer_pin said:

This is something I am not good at right now and I was wondering if you could provide guidance on what possible resource I can look up to better understand these terminologies or what topic/subject are they tackled in.

For figuring out the meaning of specific words being used, like prescaler, I think the best way to go about it is to google it as you encounter them. I do not know of a single source that covers these from start to finish, but I also think that would be a very tiresome way of learning their meaning.
Instead, I recommend that you google each of them as they are encountered, and make a small note to yourself about their meaning.
Registers for example is a central topic in embedded programming, which basically boils down to literal transistor states.

I highly recommend reading an introduction to embedded programming to better grasp the concepts of registers and register manipulation.

refer_pin said:

Yup, I think it's a really simple program to start studying to get familiar with. I'm a bit confuse where I can read up on "_WFI()" and "NRF_SUCCESS"? It's my first time seeing them in C

_WFI (wait for event) is a CPU function that places the CPU in a low-power POWER ON mode. The CPU will thus use less power while nothing is happening, but as soon as something happens ( an event is generated ) it will be ready to go. You will see that in most of the examples from the SDK the main loop of the program primarily does one thing - such as calling the idle_state_handler function - which essentially is to go into this low-power POWER ON mode. This is one of the main differences between Arduino programming and embedded C programming - while the program in Arduino often is based on a sequential execution of the loop function, the embedded C programs are rather based on an interrupt-event system. In short, this means that the main loop is just going to sleep ( and has the lowest priority ), and instead being interrupted from doing so whenever something needs to be done.

Lastly, NRF_SUCCESS is one of the error codes we use in the SDK, to signal that a function call was successful. This is also likely a new element when coming from Arduino development, but different driver functions might fail for different reasons, and when that happens there needs to be a proper error handling in place for the particular failure.
You will learn more about this as you go, but make sure that you have defined DEBUG in your preprocessor defines, like shown in the included image, to have a detailed error message be printed to your logger output whenever such an error is encountered.

It is therefore also essential that you pass every returned error code to an APP_ERROR_CHECK in order to verify whether the function call was successful.

This all might be a lot to take in right now, but please do not hesitate to ask if anything should be unclear - then I will try to answer as best I can.

Hope the above explanations makes things at least somewhat clearer! :) 

Best regards,
Karl

[refer_pin]

Karl Ylvisaker said:

Please also know that P0.06 is usually used for the UART TX PIN in all the SDK examples.

Hello, 

So what pins should I use for PWM output? I'm actually planning to push my code to an Adafruit nRF52840 Feather Board. I dont know if my process of coding the nRF52840 dk first then transferring the code to a Adafruit nRF52840 Feather Board is correct but that's my intial plan. Basing from the feather board schematics, my other pin options in the nRF52840 dk that's used in the feather board are 0.07, 0.08, 0.26, 0.27,1.08 and 1.09. From my pin options, what pins are suitable for producing a PWM of 400kHz? 

[Karl Ylvisaker]

Hello,

refer_pin said:

So what pins should I use for PWM output?

Please choose pints according to the Pin Assignment section of the nRF52840 Product Specification.
The important part here is to check that you are not sending a high frequency signal on pins that are located close to the radio peripheral.

Furthermore, you should also always check the Connector Interface diagram of the nRF52840 DK specification, since this will tell you which pins the DK is already using for different functionality.
If you should need any of these pins you will have to follow the Solder Bridge documentation in order to make them available ( and thus disconnect the current functionality ).

refer_pin said:

I'm actually planning to push my code to an Adafruit nRF52840 Feather Board.

I have never worked with this Adafruit module myself, but the nRF52840 SoC will still be the same - so you will just need to make sure that your program matches the pinout indicated on their board schematics. I.e if they expect UART TX to be on pin 0.06 then you should make sure this is the case in your program as well, etc.

refer_pin said:

what pins are suitable for producing a PWM of 400kHz? 

Please see the Pin assignment referenced above to determine this.
Please do not hesitate to let me know if anything should be unclear.

Best regards,
Karl

[refer_pin]

Karl Ylvisaker said:

Please see the Pin assignment referenced above to determine this.

So I looked into the Pin Assignment and Connector Interface link you sent me which is a good addition of documents to look into going forward, thanks for this. The pin that I believe would be possible to output the 400kHz PWM are P0.26 and P0.27, can you tell me if my analysis is correct or otherwise?

[Karl Ylvisaker]

refer_pin said:

So I looked into the Pin Assignment and Connector Interface link you sent me which is a good addition of documents to look into going forward, thanks for this.

I am happy to hear that you found these documents useful!
Whenever you need more pins in the future, this is exactly how you should go about choosing them.

refer_pin said:

The pin that I believe would be possible to output the 400kHz PWM are P0.26 and P0.27, can you tell me if my analysis is correct or otherwise?

Yes, your analysis here is correct - you may very well use P0.26 & P0.27 for your 400 kHz outputs, no problem.
Keep in mind that I have not checked whether P0.26 and P0.27 are already used for anything on the Feather Board you intend to use later. You should also check this, to see if these pins will be available to you when you change module as well.

Best regards,
Karl