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


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)