hello_48MHz.c

/**
 * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

#include <stdio.h>
#include "pico/stdlib.h"
#include "hardware/pll.h"
#include "hardware/clocks.h"
#include "hardware/structs/pll.h"
#include "hardware/structs/clocks.h"

void measure_freqs(void) {
    uint f_pll_sys = frequency_count_khz(CLOCKS_FC0_SRC_VALUE_PLL_SYS_CLKSRC_PRIMARY);
    uint f_pll_usb = frequency_count_khz(CLOCKS_FC0_SRC_VALUE_PLL_USB_CLKSRC_PRIMARY);
    uint f_rosc = frequency_count_khz(CLOCKS_FC0_SRC_VALUE_ROSC_CLKSRC);
    uint f_clk_sys = frequency_count_khz(CLOCKS_FC0_SRC_VALUE_CLK_SYS);
    uint f_clk_peri = frequency_count_khz(CLOCKS_FC0_SRC_VALUE_CLK_PERI);
    uint f_clk_usb = frequency_count_khz(CLOCKS_FC0_SRC_VALUE_CLK_USB);
    uint f_clk_adc = frequency_count_khz(CLOCKS_FC0_SRC_VALUE_CLK_ADC);
#ifdef CLOCKS_FC0_SRC_VALUE_CLK_RTC
    uint f_clk_rtc = frequency_count_khz(CLOCKS_FC0_SRC_VALUE_CLK_RTC);
#endif

    printf("pll_sys  = %dkHz\n", f_pll_sys);
    printf("pll_usb  = %dkHz\n", f_pll_usb);
    printf("rosc     = %dkHz\n", f_rosc);
    printf("clk_sys  = %dkHz\n", f_clk_sys);
    printf("clk_peri = %dkHz\n", f_clk_peri);
    printf("clk_usb  = %dkHz\n", f_clk_usb);
    printf("clk_adc  = %dkHz\n", f_clk_adc);
#ifdef CLOCKS_FC0_SRC_VALUE_CLK_RTC
    printf("clk_rtc  = %dkHz\n", f_clk_rtc);
#endif

    // Can't measure clk_ref / xosc as it is the ref
}

int main() {
    stdio_init_all();

    printf("Hello, world!\n");

    measure_freqs();

    // Change clk_sys to be 48MHz. The simplest way is to take this from PLL_USB
    // which has a source frequency of 48MHz
    clock_configure(clk_sys,
                    CLOCKS_CLK_SYS_CTRL_SRC_VALUE_CLKSRC_CLK_SYS_AUX,
                    CLOCKS_CLK_SYS_CTRL_AUXSRC_VALUE_CLKSRC_PLL_USB,
                    48 * MHZ,
                    48 * MHZ);

    // Turn off PLL sys for good measure
    pll_deinit(pll_sys);

    // CLK peri is clocked from clk_sys so need to change clk_peri's freq
    clock_configure(clk_peri,
                    0,
                    CLOCKS_CLK_PERI_CTRL_AUXSRC_VALUE_CLK_SYS,
                    48 * MHZ,
                    48 * MHZ);

    // Re init uart now that clk_peri has changed
    stdio_init_all();

    measure_freqs();
    printf("Hello, 48MHz");

    return 0;
}