Does Zephyr support PPI/SPIM communication?

[Wael]

Hello All,

 

I hope all is well. I have now been using Nordic ICs for close to 10 years and have become familiar with SDK5 and developed multiple applications using it. I am currently in the process of trying to learn the new Zephyr SDK for our new design and have made some nice progress. Where I am currently stuck is I need to use PPI to communicate with external peripherals and I am not sure which path I should go down on. From what I have been reading, it seems to me that in order to use PPI with SPIM, one must use the nrfx driver instead of the Zephyr. Here are few questions and concerns that I have:

 

1. Is there a way to implement PPI/SPIM using the Zephyr SDK?
2. If one must use the nrfx driver, what are the long-term repercussions? For example, I have read that if you one uses the nrfx driver, the power management unit(PMU) system will not know anything about the SPI instance and functions; and hence, it can not optimize power for it. If that is the case, doesn’t this almost render the use of PPI inadequate?
3. I don't see any flags like NRFX_SPIM_FLAG_HOLD_XFER, and/or  NRFX_SPIM_FLAG_TX_POSTINC for PPI implementation. 
4. Is there an example for the nRF52833 that shows how to implement PPI using Zephyr driver. there really needs to be more examples and documentations on this subject. any links and/or examples would be greatly appreciated.   

 

I have already coded my peripheral SPI communications using the Zephyr driver and now may have to restart from the beginning if PPI is not supported in the Zephyr SDK. These are some of the questions and concerns that I have. As always, your help is greatly appreciated and I look forward to all your responses.

 

Regards,

[Edvin]

You may want to have a look at this guide:

 nRF Connect SDK Tutorial - Part 2 | NCS v1.2.0 

Search for "I2C_NRFX" in that guide. Obviously, it uses I2C instead of SPI, but the method is the same.

BR,

Edvin

[Wael]

hi Edvin,

thanks for taking the time to answer my questions. it seems that the Zephyr CONFIG_GPIO=n needs to be set. if so, does this mean all my GPIO pins need to be configured in the nrfx driver and not in the proj.conf? 

Thanks

[Edvin]

Wael said:

it seems that the Zephyr CONFIG_GPIO=n

That sounds strange. What did you base that conclusion on?

BR,

Edvin

[Wael]

hi Edvin,

in this example, 

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/zephyr/samples/boards/nrf/nrfx/README.html

it states "Zephyr GPIO driver is disabled to prevent it from registering its own handler for the GPIOTE interrupt"

I am assuming this will create conflicting GPIOTE interrupts based on the above statement.

Regards,

[Edvin]

Ah, I see. That makes sense.

I believe it means that all (pure) gpio pins needs to be controlled through the nrfx driver. I believe (but I am not 100% sure) that you can still use other peripherals through standard zephyr configuration, but not the GPIO module.

NB: It is also possible to do this very much bare metal in NCS by using the registers. I did a hands-on task at one point, which you can have a look at if you like:

https://github.com/edvinand/ppi_pwm_hands_on/blob/main/src/suggested_solution_main.c

Best regards,

Edvin

Best regards,

Edvin