Internal and Unstable APIs

This section is listing some APIs that are internal or likely to be changed or removed in the next releases of ESP-IDF.

API Reference

Header File


void esp_rom_software_reset_system(void)

Software Reset digital core include RTC.

It is not recommended to use this function in esp-idf, use esp_restart() instead.

void esp_rom_software_reset_cpu(int cpu_no)

Software Reset cpu core.

It is not recommended to use this function in esp-idf, use esp_restart() instead.


cpu_no -- : The CPU to reset, 0 for PRO CPU, 1 for APP CPU.

int esp_rom_printf(const char *fmt, ...)

Print formated string to console device.


float and long long data are not supported!

  • fmt -- Format string

  • ... -- Additional arguments, depending on the format string


int: Total number of characters written on success; A negative number on failure.

void esp_rom_delay_us(uint32_t us)

Pauses execution for us microseconds.


us -- Number of microseconds to pause

void esp_rom_install_channel_putc(int channel, void (*putc)(char c))

esp_rom_printf can print message to different channels simultaneously. This function can help install the low level putc function for esp_rom_printf.

  • channel -- Channel number (startting from 1)

  • putc -- Function pointer to the putc implementation. Set NULL can disconnect esp_rom_printf with putc.

void esp_rom_install_uart_printf(void)

Install UART1 as the default console channel, equivalent to esp_rom_install_channel_putc(1, esp_rom_uart_putc)

soc_reset_reason_t esp_rom_get_reset_reason(int cpu_no)

Get reset reason of CPU.


cpu_no -- CPU number


Reset reason code (see in soc/reset_reasons.h)

void esp_rom_route_intr_matrix(int cpu_core, uint32_t periph_intr_id, uint32_t cpu_intr_num)

Route peripheral interrupt sources to CPU's interrupt port by matrix.

Usually there're 4 steps to use an interrupt:

  1. Route peripheral interrupt source to CPU. e.g. esp_rom_route_intr_matrix(0, ETS_WIFI_MAC_INTR_SOURCE, ETS_WMAC_INUM)

  2. Set interrupt handler for CPU

  3. Enable CPU interrupt

  4. Enable peripheral interrupt

  • cpu_core -- The CPU number, which the peripheral interrupt will inform to

  • periph_intr_id -- The peripheral interrupt source number

  • cpu_intr_num -- The CPU (external) interrupt number. On targets that use CLIC as their interrupt controller, this number represents the external interrupt number. For example, passing cpu_intr_num = i to this function would in fact bind peripheral source to CPU interrupt CLIC_EXT_INTR_NUM_OFFSET + i.

uint32_t esp_rom_get_cpu_ticks_per_us(void)

Get the real CPU ticks per us.


CPU ticks per us

void esp_rom_set_cpu_ticks_per_us(uint32_t ticks_per_us)

Set the real CPU tick rate.


Call this function when CPU frequency is changed, otherwise the esp_rom_delay_us can be inaccurate.


ticks_per_us -- CPU ticks per us