esp-idf/components/bootloader_support/src/bootloader_clock.c

// Copyright 2017 Espressif Systems (Shanghai) PTE LTD
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "rom/uart.h"
#include "rom/rtc.h"
#include "soc/soc.h"
#include "soc/rtc.h"
#include "soc/dport_reg.h"
#include "soc/efuse_reg.h"
#include "soc/rtc_cntl_reg.h"

void bootloader_clock_configure()
{
    // ROM bootloader may have put a lot of text into UART0 FIFO.
    // Wait for it to be printed.
    // This is not needed on power on reset, when ROM bootloader is running at
    // 40 MHz. But in case of TG WDT reset, CPU may still be running at >80 MHZ,
    // and will be done with the bootloader much earlier than UART FIFO is empty.
    uart_tx_wait_idle(0);

    /* Set CPU to 80MHz. Keep other clocks unmodified. */
    int cpu_freq_mhz = 80;

    /* On ESP32 rev 0, switching to 80MHz if clock was previously set to
     * 240 MHz may cause the chip to lock up (see section 3.5 of the errata
     * document). For rev. 0, switch to 240 instead if it was chosen in
     * menuconfig.
     */
    uint32_t chip_ver_reg = REG_READ(EFUSE_BLK0_RDATA3_REG);
    if ((chip_ver_reg & EFUSE_RD_CHIP_VER_REV1_M) == 0 &&
            CONFIG_ESP32_DEFAULT_CPU_FREQ_MHZ == 240) {
        cpu_freq_mhz = 240;
    }

    rtc_clk_config_t clk_cfg = RTC_CLK_CONFIG_DEFAULT();
    clk_cfg.xtal_freq = CONFIG_ESP32_XTAL_FREQ;
    clk_cfg.cpu_freq_mhz = cpu_freq_mhz;
    clk_cfg.slow_freq = rtc_clk_slow_freq_get();
    clk_cfg.fast_freq = rtc_clk_fast_freq_get();
    rtc_clk_init(clk_cfg);
    /* As a slight optimization, if 32k XTAL was enabled in sdkconfig, we enable
     * it here. Usually it needs some time to start up, so we amortize at least
     * part of the start up time by enabling 32k XTAL early.
     * App startup code will wait until the oscillator has started up.
     */
#ifdef CONFIG_ESP32_RTC_CLOCK_SOURCE_EXTERNAL_CRYSTAL
    if (!rtc_clk_32k_enabled()) {
        rtc_clk_32k_bootstrap(CONFIG_ESP32_RTC_XTAL_BOOTSTRAP_CYCLES);
    }
#endif
}