nRF52840 - giving userdefined function at PPI task end

[Aliasgar Surti]

Hello,

We were just wondering if it is possible to give user-defined function at the PPI TEP instead of starting timer or generating some GPIOTE task.

Is it possible to configure a PPI channel where there is a GPIOTE event and as per the occurrence of that event, some userdefined function executes?

nrf_drv_ppi_channel_assign(m_ppi_channel1,
                           gpiote_event_addr,
                           &user_defined_function);

I tried above way, it compiled but the function is not getting executed on GPIOTE event.

I can't use the timer interrupt for this as the frequency of GPIOTE event is really high (around 3MHz). And I want to capture 8-bit parallel port data in 'user_defined_function'

So, Can I make above logic work anyhow? Is it possible in PPI? Any suggestions how can I achieve this one?

Thanks in advance.

[Edvin]

Hello,

Sorry, the previous reply was from a spam-bot. I reported it, and the reply was deleted, along with your answer to it. 

You can try to use EGU (event generator unit) to trigger a SW interrupt event from the PPI. To get some help to set it up, check out this ticket, and let me know if you are stuck somewhere.

[Aliasgar Surti]

Okay, understood the concept of EGU.

But didn't get how to make it functional.

Can you please provide a demo code for that? or any further reference regarding that will be useful.

Thanks.

[Edvin]

can you try to trigger the PPI event less often, i.e. have an input pulse with a lower frequency to see if this is actually the issue? (you can use a timer to generate a pulse on one of the GPIOs that you input to your PPI pin)

[Aliasgar Surti]

I don't think that is the issue, this is because when I remove the input pulse from the GPIO then also the counter keeps on increment.

I tried with timer of 10ms. Then also, when first event occurs at PPI event end, the execution of SWI1_EGU1_IRQHandler() starts endlessly. If I remove the input pulse at runtime (by removing input from GPIO pin) then also the counter keeps on increment.

[Edvin]

Is it possible to reproduce this on a DK? If so, would it be possible to send a project that can reproduce this, so that I can test it and see what's going on?

Best regards,

Edvin

[Aliasgar Surti]

Yes, it is possible to reproduce on DK. Timer interrupt toggles pin 0.05 on DK and EGU is triggered by the event on pin 0.02

Attached is the project.

Thanks.

nrf52-ble-image-transfer-demo.zip

[Edvin]

Hello,

Sorry. I should have noticed.

In your egu event handler you should use:

NRF_EGU1->EVENTS_TRIGGERED[0] = 0;

not

NRF_EGU1->TASKS_TRIGGER[0] = 0;

I also see that something triggered NRF_EGU1->EVENTS_TRIGGERED[1]. Not sure exactly what that is. I didn't get the time to look properly at it, but maybe you figure it out before tomorrow (Not sure where you are situated). 

So I added:

NRF_EGU1->EVENTS_TRIGGERED[0] = 0;
NRF_EGU1->EVENTS_TRIGGERED[1] = 0;

And then it stopped calling the EGU event handler. Maybe some other library is using EGU1, and you can try another EGU (to prevent EVENTS_TRIGGERED[1] from triggereng the event handler.

Best regards,

Edvin

[Aliasgar Surti]

Hello,

Thanks for your suggestion. Now there is no unnecessary interrupts when the pulse is removed from the GPIO.

As we have a very narrow timeline for capturing the image, we want to calculate the machine cycle of the subroutine and total available machine cycles for the controller. Is there any document/reference from where we can get this information?

Also, we are capturing parallel port data. Is there any better way for storing the image on device? I have gone through the demo of flash data storage. Will it be appropriate to use flash storage considering very tight timeline (high rate of input data)?

Can we write subroutine for EGU in assembly? Will it reduce number of machine cycles it takes to execute the subroutine?

Thanks.