Face and PacketHandler in NDNph

Face is an overloaded term in Named Data Networking (NDN). My last article explained what is a face in NDN forwarders and NDN libraries, and then described the endpoint design in my NDNts library. This time, I'll introduce a unique face API design in my NDNph library.

NDNph is a C++ header-only library that enables low level application development. It supports multiple platforms, but is primarily designed for microcontrollers with limited hardware resources. In particular, RAM capacity is very limited, with typical values ranging from 50KB (ESP8266) to 320KB (ESP32). This necessitates a different API design for the face.

Overhead of a Traditional Face

Traditionally, a face in NDN libraries has the following features:

  • send and receive NDN network layer packets
  • match incoming Data against outgoing Interests
  • keep track of Interest timeouts
  • dispatch incoming Interests to producer callback functions

Is ESP32 Big Endian or Little 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.

Introducing NDNph and New Version of esp8266ndn

NDNph is my latest Named Data Networking (NDN) client library. This article gives an overview of this library.

History and Motivation

In 2016, I started esp8266ndn. It contains a copy of ndn-cpp-lite, UCLA REMAP's C++ library that does not use dynamic memory allocations. I then added integrations with ESP8266's network stack and crypto functions, making esp8266ndn the first NDN library that works on the ESP8266 microcontroller. Using this library, I built several projects, including a wearable jewelry and a call button. University of Memphis also deployed several sensor nodes using esp8266ndn.

Over the years, esp8266ndn gained many new features, and widened platform support to include ESP32 and nRF52. However, using ndn-cpp-lite as the core is becoming problematic:

  • New protocol features show up slowly, because ndn-cpp-lite author would not add a feature until ndn-cxx has it, and design discussions for ndn-cxx sometimes take several years.
  • There is no generic TLV encoder/decoder, making it difficult to support TLV structures in application layer.
  • ndn-cpp-lite is bloated with obsolete features, due to their backwards compatibility guarantees. Consequently, binary code size is unnecessarily large.
  • Although I can add patches to ndn-cpp-lite during importing into esp8266ndn, it has been difficult to test these patches. This isn't ndn-cpp-lite's fault, but is still an issue.

Loud Pumpkin with Circuit Playground

It's October. Pumpkins are filling the grocery stores. This means one thing: Halloween is coming!

I'm told that I'm supposed to wear a costume on Halloween. However, I'm too broke to buy an outfit for just one day, so I'm going to wear a colorful circuit board instead. This year, I'm going to become a pumpkin. Well, sorta.

The board is an Adafruit Circuit Playground Express. It packs 10 NeoPixel LEDs that can display any color, four sensors, and a few buttons. My code uses the microphone sensor to measure how loud is the environment. Based on measured sound pressure, it then lights up a number of NeoPixels to #ff7619 the "pumpkin color".

#include <Adafruit_CircuitPlayground.h>

void setup() {

void loop() {
  float sp = CircuitPlayground.mic.soundPressureLevel(100);
  int peak = map(sp, 56, 90, 0, 9);

  for (int i = 0; i <= peak; ++i) {
    CircuitPlayground.strip.setPixelColor(i, 0xff7619);

How to Print uint64_t in Arduino

The Arduino programming language looks like C++, but it is weird in its own way: there's no C++ standard library. In C++, you can print a variable to the debug console with std::cerr << x;. In Arduino, you have to write a function call: Serial.print(x);. I love that the Streaming library brings back the familiar syntax Serial << x; through some template and macro magic. But when it comes to a uint64_t variable, nothing works!

error: call of overloaded 'print(uint64_t&)' is ambiguous

note: candidates are:
note: size_t Print::print(const __FlashStringHelper*) <near match>
note:   no known conversion for argument 1 from 'uint64_t {aka long long unsigned int}' to 'const __FlashStringHelper*'
note: size_t Print::print(const String&) <near match>
note:   no known conversion for argument 1 from 'uint64_t {aka long long unsigned int}' to 'const String&'

The cause of this error is: Arduino does not know how to print a uint64_t!

How Arduino Prints Stuff

Arduino contains a subset of C++ standard library, plus some additional headers known as the "Arduino Core". Each microcontroller has its own Arduino Core: AVR, SAMD, ESP8266, ESP32. They follow roughly the same API, one of which is the Print class that knows how to print stuff.