src/rp2_common/pico_runtime_init/runtime_init_clocks.c

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

#include "pico/runtime_init.h"
#if !PICO_RUNTIME_NO_INIT_CLOCKS

#include "hardware/clocks.h"
#include "hardware/pll.h"
#include "hardware/ticks.h"
#include "hardware/xosc.h"
#if PICO_RP2040
#include "hardware/regs/rtc.h"
#endif

#if PICO_RP2040
// The RTC clock frequency is 48MHz divided by power of 2 (to ensure an integer
// division ratio will be used in the clocks block).  A divisor of 1024 generates
// an RTC clock tick of 46875Hz.  This frequency is relatively close to the
// customary 32 or 32.768kHz 'slow clock' crystals and provides good timing resolution.
#define RTC_CLOCK_FREQ_HZ       (USB_CLK_HZ / 1024)
#endif

static void start_all_ticks(void) {
    uint32_t cycles = clock_get_hz(clk_ref) / MHZ;
    // Note RP2040 has a single tick generator in the watchdog which serves
    // watchdog, system timer and M0+ SysTick; The tick generator is clocked from clk_ref
    // but is now adapted by the hardware_ticks library for compatibility with RP2350
    // npte: hardware_ticks library now provides an adapter for RP2040

    for (int i = 0; i < (int)TICK_COUNT; ++i) {
        tick_start((tick_gen_num_t)i, cycles);
    }
}

void __weak runtime_init_clocks(void) {
    // Note: These need setting *before* the ticks are started
    if (running_on_fpga()) {
        for (uint i = 0; i < CLK_COUNT; i++) {
            clock_set_reported_hz(i, 48 * MHZ);
        }
        // clk_ref is 12MHz in both RP2040 and RP2350 FPGA
        clock_set_reported_hz(clk_ref, 12 * MHZ);
        // RP2040 has an extra clock, the rtc
#if HAS_RP2040_RTC
        clock_set_reported_hz(clk_rtc, RTC_CLOCK_FREQ_HZ);
#endif
    } else {
        // Disable resus that may be enabled from previous software
        clocks_hw->resus.ctrl = 0;

        // Enable the xosc
        xosc_init();

        // Before we touch PLLs, switch sys and ref cleanly away from their aux sources.
        hw_clear_bits(&clocks_hw->clk[clk_sys].ctrl, CLOCKS_CLK_SYS_CTRL_SRC_BITS);
        while (clocks_hw->clk[clk_sys].selected != 0x1)
            tight_loop_contents();
        hw_clear_bits(&clocks_hw->clk[clk_ref].ctrl, CLOCKS_CLK_REF_CTRL_SRC_BITS);
        while (clocks_hw->clk[clk_ref].selected != 0x1)
            tight_loop_contents();

        /// \tag::pll_init[]
        pll_init(pll_sys, PLL_SYS_REFDIV, PLL_SYS_VCO_FREQ_HZ, PLL_SYS_POSTDIV1, PLL_SYS_POSTDIV2);
        pll_init(pll_usb, PLL_USB_REFDIV, PLL_USB_VCO_FREQ_HZ, PLL_USB_POSTDIV1, PLL_USB_POSTDIV2);
        /// \end::pll_init[]

        // Configure clocks

        // RP2040 CLK_REF = XOSC (usually) 12MHz / 1 = 12MHz
        // RP2350 CLK_REF = XOSC (XOSC_MHZ) / N (1,2,4) = 12MHz

        // clk_ref aux select is 0 because:
        //
        // - RP2040: no aux mux on clk_ref, so this field is don't-care.
        //
        // - RP2350: there is an aux mux, but we are selecting one of the
        //   non-aux inputs to the glitchless mux, so the aux select doesn't
        //   matter. The value of 0 here happens to be the sys PLL.

        clock_configure_undivided(clk_ref,
                        CLOCKS_CLK_REF_CTRL_SRC_VALUE_XOSC_CLKSRC,
                        0,
                        XOSC_HZ);

        /// \tag::configure_clk_sys[]
        // CLK SYS = PLL SYS (usually) 125MHz / 1 = 125MHz
        clock_configure_undivided(clk_sys,
                        CLOCKS_CLK_SYS_CTRL_SRC_VALUE_CLKSRC_CLK_SYS_AUX,
                        CLOCKS_CLK_SYS_CTRL_AUXSRC_VALUE_CLKSRC_PLL_SYS,
                        SYS_CLK_HZ);
        /// \end::configure_clk_sys[]

        // CLK USB = PLL USB 48MHz / 1 = 48MHz
        clock_configure_undivided(clk_usb,
                        0, // No GLMUX
                        CLOCKS_CLK_USB_CTRL_AUXSRC_VALUE_CLKSRC_PLL_USB,
                        USB_CLK_HZ);

        // CLK ADC = PLL USB 48MHZ / 1 = 48MHz
        clock_configure_undivided(clk_adc,
                        0, // No GLMUX
                        CLOCKS_CLK_ADC_CTRL_AUXSRC_VALUE_CLKSRC_PLL_USB,
                        USB_CLK_HZ);

#if HAS_RP2040_RTC
        // CLK RTC = PLL USB 48MHz / 1024 = 46875Hz
#if (USB_CLK_HZ % RTC_CLOCK_FREQ_HZ == 0)
        // this doesn't pull in 64 bit arithmetic
        clock_configure_int_divider(clk_rtc,
                        0, // No GLMUX
                        CLOCKS_CLK_RTC_CTRL_AUXSRC_VALUE_CLKSRC_PLL_USB,
                        USB_CLK_HZ,
                        USB_CLK_HZ / RTC_CLOCK_FREQ_HZ);

#else
        clock_configure(clk_rtc,
                        0, // No GLMUX
                        CLOCKS_CLK_RTC_CTRL_AUXSRC_VALUE_CLKSRC_PLL_USB,
                        USB_CLK_HZ,
                        RTC_CLOCK_FREQ_HZ);

#endif
#endif

        // CLK PERI = clk_sys. Used as reference clock for UART and SPI serial.
        clock_configure_undivided(clk_peri,
                        0,
                        CLOCKS_CLK_PERI_CTRL_AUXSRC_VALUE_CLK_SYS,
                        SYS_CLK_HZ);

#if HAS_HSTX
        // CLK_HSTX = clk_sys. Transmit bit clock for the HSTX peripheral.
        clock_configure_undivided(clk_hstx,
                        0,
                        CLOCKS_CLK_HSTX_CTRL_AUXSRC_VALUE_CLK_SYS,
                        SYS_CLK_HZ);
#endif
    }

    // Finally, all clocks are configured so start the ticks
    // The ticks use clk_ref so now that is configured we can start them
    start_all_ticks();
}

#endif