SDConnect on nRF5340 : using UARTE with unknown rx length

[BrianW]

I am struggling with the same requirement as this ticket :  RE: NRFX UART RX CONTINUOUS RECEIVE where RX LEN is unknown 

ie receive from a UARTE without knowing in advance how many rx bytes to expect. This is typical for exchanging AT type commands on a UART with another system...the receiver doesn't know how long the command being sent is going to be. In my previous nRF51/nRF52 projects, I just use UART ISR to get each byte, add to my fifo buffer, and detect LF/CR to know when I got a complete line...but this was before SDKConnect and not using UARTE.

Some questions:

 - Using an nRF5340, its seems my only option is to use SDKConnect with Zephyr, yes? No more SoftDevice builds?

- do I understand correctly that the nrf5340 does NOT support basic UART, only UARTE? Only EasyDMA operation is possible (in the same way it doesn't seem to support TWI, only TWIM)

- I have multiple UARTs to service - but if as per the final reply in the ticket above I have to use 2 timers per channel (one to count bytes received, one to do the 'idle line' timeout) it seems I won't have enough timers?

what is the correct way to handle a UART on the nrf5340 for this use case?

Thanks

Brian

btw, I did look at the tutorials, but they are very basic (and use the zephyr driver which uses the same timer mechanism) so weren't much help... But if there is a good sample that is useable for a real application Id be very happy...

[Vidar Berg]

Hello,

Using an nRF5340, its seems my only option is to use SDKConnect with Zephyr, yes? No more SoftDevice builds?

This is correct. Instead of using the Softdevice which implements the Bluetooth host and Bluetooth controller, we now have a Softdevice controller which typically reside on the network core, and the Zephyr host on the application. Communication between host and controller is through the standard HCI interface. You can read more about the architecture here: https://docs.nordicsemi.com/bundle/ncs-latest/page/nrf/device_guides/nrf53/features_nrf53.html#protocols_and_use_cases_for_the_nrf5340_dk

- do I understand correctly that the nrf5340 does NOT support basic UART, only UARTE? Only EasyDMA operation is possible (in the same way it doesn't seem to support TWI, only TWIM)

Yes, the nRF5340 does not include the legacy serial peripherals without easyDMA.

- I have multiple UARTs to service - but if as per the final reply in the ticket above I have to use 2 timers per channel (one to count bytes received, one to do the 'idle line' timeout) it seems I won't have enough timers?

The idle timeout timer is a Zephyr timer instance which runs off the system clock (RTC) . Byte counting with a TIMERs and PPI is optional, and is enabled through these Kconfig symbols: https://github.com/nrfconnect/sdk-zephyr/blob/35aedfa532875b79524a00267cdaaa17ca3049f5/drivers/serial/Kconfig.nrfx#L82 

Best regards,

Vidar

 https://docs.nordicsemi.com/bundle/ncs-latest/page/zephyr/hardware/peripherals/uart.html 

[BrianW]

Thanks for the info.

Looking then at the Zephyr system uart driver implementation  (as per the link):

- can I use it in  'interrupt driven API' mode on an nRF5340?

- is there a code example/sample of an application that uses this mode?

- in this mode, how many UART devices can I open like this simultaneously? (ie does each instance use a resource like a TIMER/PPI to do its byte counting?)

- how (non)efficient is this mode compared to 'asynchronous API' mode? (in terms of CPU overhead at a specific baud rate when the data is arriving at that rate (ie no idle periods)

thanks

Brian