CPU Frequency Scaling Issue on Raspberry Pi 4B with Zephyr RTOS

[LLLJYAA]

Hi everyone,

I'm working on a project with Zephyr RTOS on a Raspberry Pi 4B. I noticed that the CPU frequency is reported as 600 MHz instead of the expected 1.5 GHz. Here are some details:

Device: Raspberry Pi 4B
Expected CPU Frequency: 1.5 GHz
Observed CPU Frequency: 600 MHz
I’ve written a simple application to measure the CPU frequency using cycle counters. Here’s the code snippet I’m using:

#include <zephyr/kernel.h>
#include <zephyr/sys/printk.h>
#include <zephyr/device.h>
#include <stdint.h>
#include <zephyr/sys_clock.h>

// Call sequence:
	1. Enable CPU counter:
	enable_cycle_counter_el0()
	2. Get CPU counter:
	uint64_t u64Time = get_cpu_cnt();
*/

void main(void)
{
    printk("Enabling cycle counter\n");
    enable_cycle_counter_el0();

    while (1) {
        uint64_t start_cnt = get_cpu_cnt();
        
        delay_us(1000000);

        uint64_t end_cnt = get_cpu_cnt();

        printk("Start count: %llu\n", start_cnt);
        printk("End count: %llu\n", end_cnt);
        printk("Elapsed cycles: %llu\n", end_cnt - start_cnt);
    }
}

From my understanding, Zephyr RTOS does not have built-in support for CPU frequency scaling governors. However, I’m looking for confirmation on this and any possible solutions or workarounds to ensure the CPU runs at the expected 1.5 GHz frequency.

Questions:
Is it true that Zephyr RTOS itself does not support CPU frequency scaling governors?
What are the recommended steps to ensure the Raspberry Pi 4B operates at its maximum CPU frequency when running Zephyr RTOS?
Are there any specific configurations or patches available for Zephyr RTOS that can help manage CPU frequency scaling on Raspberry Pi 4B?
Any help or guidance would be greatly appreciated.

Thank you!

[LLLJYAA]

add a line "arm_freq_min=1500" in conf.txt