Configuring multiple UARTs on nRF5340DK (plus other serial interfaces)

[Sydney]

I'm using the nRF5340 (currently nRF5340DK with custom hardware following shortly) and NCS 1.6.0. I'm working on a project that needs at least two UARTs and one SPI master interface, but I haven't been able to find an example to base this on and I can't seem to find the right combination of settings. It looks like there may also be considerations like shared resources between UART/SPI/TWI that must be configured correctly. I've also noticed the comment in v1.6.0/nrf/samples/CMakeLists.txt that says we can’t use UART1 because it’s used by the TF-M secure application. We can move debug logging from UART0 to RTT if needed to free up the UART0 resource. Is there an example that I've overlooked that clearly shows how to configure this? Or can someone explain what needs to be done? Configuring serial interfaces should be relatively straightforward but we just can't seem to get it right and I'm having a hard time tracking down what exactly is misconfigured.

If it matters, we may also need a separate configuration with one UART, one SPI master, and one TWI master. I'm hoping/assuming that will be straightforward once we see how to implement 2xUART and 1xSPI master but if there are any other tricky settings to know about if we need to replace one UART with a TWI master, I'd be interested in hearing about those settings.

Thanks.

[Øyvind]

Hello, 

My apologies for the late reply. What version of the nRF5340DK are you working on?

 

I haven't been able to find an example to base this on and I can't seem to find the right combination of settings.

 No, there is unfortunately not many samples on peripherals available in NCS/nrf repo. There are some in the Zephyr repo, however, they might not be tested with the nRF5340DK.

If you are new to the nRF5340 and NCS, please have a look at the nRF Connect SDK tutorial, it's currently a little outdated, but it gives an overview. 

 There have been similar questions on DevZone. Have a look at this answer from my colleague Didrik. There are some samples available in this link, however, not sure what the current status is

It looks like there may also be considerations like shared resources between UART/SPI/TWI that must be configured correctly.

 Yes, please see the App Core Peripheral Instantiation chapter in the nRF5340 Product Specification.

 

I've also noticed the comment in v1.6.0/nrf/samples/CMakeLists.txt that says we can’t use UART1 because it’s used by the TF-M secure application.

 Have you read the documentation on TF-M in our NCS documentation?  By default, our samples use Secure Partition Manager (SPM).

 

 

we may also need a separate configuration with one UART, one SPI master, and one TWI master

 Not sure what you mean. All configurations are done in the .dts and .overlay files e.g. nRF5340DK DTS files found in the Zephyr board folder. Read more about these in the Devicetree guide.

Kind regards,
Øyvind

[Sydney]

Sorry, I'm not sure how to reply in line without the nested quotes becoming a mess, so I'll try to make it clear what I'm responding to.

• I'm using nRF5340DK 0.11.0 according to the sticker on the top of the board.
• I think I had seen that thread you linked about UARTs on the nRF9160, but the nRF9160DK dts file already has two UARTs in it so it's easy to use both, but the nRF5340DK dts file only has one UART. >>> Actually while writing this I checked again, and it looks like a "arduino_serial: &uart1" was added to nrf5340_cpuapp_common.dts when I updated from NCS 1.5.1 to 1.6.0. So maybe that was part of my issue. But still generally what I don't have a clear answer on is what exactly do I need to put in an overlay file (and/or other settings files) to allow me to use a UART or other peripheral that is not defined in the dts files for the DK?
• Regarding TF-M, I thought I read that TF-M was the default as of NCS 1.6.0 but I might've misunderstood.
• Regarding my comment about needing a second configuration that uses TWI instead of a second UART, I just meant that we're working on two variations of this board and one might have UART, SPI, and TWI instead of UART, UART, and SPI, and I wondered if there were any other issues to consider with that second configuration.

I've read through tutorials and blogs and documentation and watched videos on the Nordic Youtube channel and I understand conceptually what I'm supposed to do with dts files and overlays, but I still seem to be missing something. Are there corresponding changes I need to make to my prj.conf that I'm overlooking for example? I appreciate your detailed response and I apologize if my frustration comes through, but as a long time user of nRF52 and nRF5 SDK, the difficulty with something as simple as enabling a peripheral in this new SDK is discouraging.

[Carl Richard]

Hello, Sydney!

It's regrettable to hear about your experiences with our SDK. I definitely agree that the documentation and samples on using peripherals is lackluster and I can assure you that work is being done to improved this. That will likely take some time, however, so I will give you a brief overview of how you can enable and use peripherals in NCS:

1. Enable the peripheral drivers in the project configuration. To ensure that the drivers for UART and SPI are enabled you can add the following KConfig options to the prj.conf:

#Enable UART driver
CONFIG_UART=y

#Enable SPIM driver
CONFIG_SPI=y
CONFIG_NRX_SPIM0=y 

Notes:
- I'm using SPIM0 here, but you can of course enable any of the other SPIM instances. Make sure to account for that in the steps below as well. 

2. Configure the hardware peripherals. This is done by using a device tree overlay for your given board. In your case you should add a file to your project called "nrf5340dk_nrf5340_cpuapp.overlay", which should contain some something like this:

&spi0 {
  status = "okay";
  label = "SPI_0"; 
};

&uart0 {
    status = "disabled";
};

&uart1 {
    compatible = "nordic,nrf-uarte";
    status = "okay";
    label = "UART_1";
    current-speed = < 115200 >;
    tx-pin = < 14 >;
    rx-pin = < 16 >;
    rts-pin = < 13 >;
    cts-pin = < 15 >;
};

&uart2 {
    compatible = "nordic,nrf-uarte";
    status = "okay";
    label = "UART_1";
    current-speed = < 115200 >;
    tx-pin = < 9 >;
    rx-pin = < 10 >;
    rts-pin = < 11 >;
    cts-pin = < 12 >;
};

Notes:
- The different configuration options for the peripherals can be found in the DTS Bindings documentation. In your case nordic,nrf-spi and nordic,nrf-uarte are the relevant bindings.
- Notice that UART0 is explicitly disabled here to ensure that SPI0 can be used. The same method applies for other instances of hardware peripherals as well.
- The configuration above uses arbitrary pins. You can choose pins on the DK freely as long as they are available. Information on this can be found in the nRF5340 DK documentation.

3. Bind and use the peripherals in the application. This is done using the Devicetree API and the respective peripheral's driver. For your reference that's SPI and UART. The binding operation would look something like this:

const struct device *spi_dev;
const struct device *uart1_dev;
const struct device *uart2_dev;
int error;

spi_dev = device_get_binding("SPI_0");
if (!spi_dev) {
    printk("Binding failed.");
    return;
}

uart1_dev = device_get_binding("UART_1");
if (!uart1_dev) {
    printk("Binding failed.");
    return;
}

uart2_dev = device_get_binding("UART_2");
if (!uart2_dev) {
    printk("Binding failed.");
    return;
}

Notes: 
- There are several examples demonstrating the binding process and usage of peripherals. I suggest having a look at our LPUART sample and some of the driver samples in Zephyr.

I hope this gives you some clarity on how to enable and use peripherals in NCS. As you suggested yourself using RTT for logging will free up one of the UARTs to do this add the following options to the project configuration:

# Config logger
CONFIG_LOG=y
CONFIG_USE_SEGGER_RTT=y
CONFIG_LOG_BACKEND_RTT=y
CONFIG_LOG_BACKEND_UART=n

Please reach out if you face any issues.

Best regards,
Carl Richard