Higher baud rate support on nrf5340

[Mohammed Ubaid]

Hi,

Just wanted to know if nrf5340dk supports for UART baud rates until 512kbps.?
And specific baud rates configuration like 122800.?

If yes, is it simply configured as in below.? or takes different configuration.?

#include <zephyr/kernel.h>
#include <zephyr/drivers/uart.h>

const struct device *uart_dev;

void main(void)
{
    uart_dev = device_get_binding("UART_0");
    if (!uart_dev) {
        printk("UART device not found!\n");
        return;
    }

    struct uart_config cfg = {
        .baudrate = 122800,
        .parity = UART_CFG_PARITY_NONE,
        .stop_bits = UART_CFG_STOP_BITS_1,
        .data_bits = UART_CFG_DATA_BITS_8,
        .flow_ctrl = UART_CFG_FLOW_CTRL_NONE,
    };

    if (uart_configure(uart_dev, &cfg) != 0) {
        printk("Failed to configure UART\n");
    } else {
        printk("UART configured to 122800 baud rate\n");
    }
}

[Kenneth]

Hi,

The baudrates that have been tested and qualified are listed here:
https://docs.nordicsemi.com/bundle/ps_nrf5340/page/uarte.html#ariaid-title53 

Make sure to start the external crystal oscillator for the HFCLK before using the uart, else the tolerance will also depend on the accuracy of the internal oscillator, which can be several % as indicated in this table:
https://docs.nordicsemi.com/bundle/ps_nrf5340/page/chapters/clock/doc/clock.html#ariaid-title67 

For baudrates not listed you will have to test them yourself to find if the accuracy fit your requirements.

Kenneth

[Mohammed Ubaid]

Hi Kenneth ,

Kenneth said:

The baudrates that have been tested and qualified are listed here:
https://docs.nordicsemi.com/bundle/ps_nrf5340/page/uarte.html#ariaid-title53 

Make sure to start the external crystal oscillator for the HFCLK before using the uart, else the tolerance will also depend on the accuracy of the internal oscillator, which can be several % as indicated in this table:
https://docs.nordicsemi.com/bundle/ps_nrf5340/page/chapters/clock/doc/clock.html#ariaid-title67 

For baudrates not listed you will have to test them yourself to find if the accuracy fit your requirements.

Thanks for the info.

Can you kindly confirm if setting of custom baud rate is as in code below or requires any additional configurations.?

#include <zephyr/kernel.h>
#include <zephyr/drivers/uart.h>

const struct device *uart_dev;

void main(void)
{
    uart_dev = device_get_binding("UART_0");
    if (!uart_dev) {
        printk("UART device not found!\n");
        return;
    }

    struct uart_config cfg = {
        .baudrate = 122800,
        .parity = UART_CFG_PARITY_NONE,
        .stop_bits = UART_CFG_STOP_BITS_1,
        .data_bits = UART_CFG_DATA_BITS_8,
        .flow_ctrl = UART_CFG_FLOW_CTRL_NONE,
    };

    if (uart_configure(uart_dev, &cfg) != 0) {
        printk("Failed to configure UART\n");
    } else {
        printk("UART configured to 122800 baud rate\n");
    }
}

[Kenneth]

Hi,

Conceptually this looks good, but the baud rate you are using is as mentioned not tested, so you will need to check how close you get to the desired baud rate. Also, looking at the code I can't seem to see that you are actually starting the high frequency clock, so you need to do this if you want to make decent measurements.

Kenneth

[Mohammed Ubaid]

Ah, got it
So i need to start HFCLK first and then configure my UART.

Thanks Kenneth .

Kenneth said:

I can't seem to see that you are actually starting the high frequency clock,

Can you point me to any code sample or snippet wherein HFCLK is enabled for UART port.?

[Kenneth]

Mohammed Ubaid said:

So i need to start HFCLK first and then configure my UART.

Each time you want to send or receive UART data you need to start the HFCLK yes, you can stop it when there is no data ro send or receive. 

Mohammed Ubaid said:

Can you point me to any code sample or snippet wherein HFCLK is enabled for UART port.?

To start the HFCLK you can for instance check out clock_init() in nrf\samples\peripheral\radio_test\.

Kenneth

[Mohammed Ubaid]

Kenneth said:

To start the HFCLK you can for instance check out clock_init() in nrf\samples\peripheral\radio_test\.

Is starting of HFCLK is sufficient.? Is there a need to route UART source as HFCLK or it is handled internally.?

[Kenneth]

Mohammed Ubaid said:

Is starting of HFCLK is sufficient.?

Yes.

Kenneth