Is ESP32 Big Endian or Little Endian?

This post is originally published on yoursunny.com blog https://yoursunny.com/t/2021/ESP32-endian/

I'm programming network protocols on the Espressif ESP32 microcontroller, and I want to know: is ESP32 big endian or little endian?
Unfortunately, search results have only videos and forum posts and PDF; the answer, if present, is buried deep in pages and pages of discussions and irrelevant content.
So I quickly wrote a little program to determine the endianness of ESP32.

The Straight Answer: ESP32 is Little Endian

I have determined that: the Tensilica Xtensa LX6 microprocessor in ESP32 is little endian.

ESP32 is little endian.
Many other processors are little endian, too:

• Intel and AMD x86 and x86_64 processors are little endian.
• Raspberry Pi and Beaglebone Black are little endian, although the underlying ARM processor may operate as big endian.
• ESP8266 is little endian. It has Tensilica Xtensa L106 microprocessor, similar to the ESP32
• nRF52 series is little endian. This includes the Adafruit Bluefruit nRF52832.

Arduino Sketch to Determine Endianness

I used this Arduino program to determine the endianness of ESP32 CPU:

void setup() {
  Serial.begin(115200);
  Serial.println();

  uint32_t x = 0x12345678;
  const uint8_t* p = reinterpret_cast<const uint8_t*>(&x);
  Serial.printf("%02X%02X%02X%02X\n", p[0], p[1], p[2], p[3]);
}

void loop() {
}

The program should print 12345678 on a big endian machine, or 78563412 on a little endian machine.
ESP32 prints:

78563412

So ESP32 is little endian.