Laboratory guide for IoT AIH students on ESP32 programming, using VREL distance labs and two types of ESP32 modules:

• ESP32 WROVER DEVKIT module - that includes (among others) dot-matrix LCD TFT display
• TTGO T5 v 2.2 module - that contains a 2.9 Waveshare e-paper, two-colour display

You can access the distant laboratory (VREL) interface here: http://distance.roboticlab.eu/.
You need to register an account (unless you have one, already). A short video presenting the account creation process and first steps is here: https://youtu.be/0R6oUWkBrpQ

You will use laboratory nodes #25 and #20:

• TTGO with e-Paper module is VREL node #25
• WROVER DEVKIT with LCD TFT module is VREL node #20

Below we present hardware details on the two modules:

This board is double-sided, on one side you will find an LCD screen (so-called back) on the other side (front) there are GPIOs connectors you connect sensors and actuators to, TF (microSD) card slot with SPI reader and an RGB LED diode (among others).
Please note you can directly observe only the back side of the module via VREL node's camera.

ESP32 provides a number of GPIOs to the developers, but some of them are hard-bound to their features as connected on the development board.

Following list present GPIOs used with the integrated hardware:

The built-in display is ILI9341 TFT display, 320×240 pixels (240×320 actually), RGB, 262k colours. Although it is possible to program it raw, we will use a ready software library to control it. This TFT display uses 16-bit per pixel memory organisation, frequently referenced as 565 (RGB, R-5-bits, G-6-bits, B-5-bits).

Correct configuration is necessary to build and deploy your code.
For ESP32 WROVER DEVKIT, a good starting point is the following content for platformio.ini file:

[env:d1_mini]
platform = espressif32
board = esp-wrover-kit
framework = arduino
upload_port = /dev/ttyUSB1
lib_deps = 
	adafruit/Adafruit-GFX-Library
	Wire
 	espressif/WROVER_KIT_LCD

Write Hello World on the LCD screen.
Using LCD display and a camera, you can observe it through, are your only interface to the devkit. Get familiar with handling LCD screen and give it a short practice, as present below.

Type textual “Hello World” on the screen. You're welcome to decorate it, change colours, size, orientation, etc.

To use LCD you must include libraries. Beginning of your .cpp source code file should then look more-less following way:

...
#include <Arduino.h>
#include <SPI.h>
#include <Adafruit_GFX.h>
#include <Adafruit_I2CDevice.h>
#include <WROVER_KIT_LCD.h>
...

Then define a controller class that manages your LCD:

...
WROVER_KIT_LCD tft;
...

Some useful functions to handle LCD operations are presented below (but not limited to):

...
  tft.fillScreen(WROVER_BLACK); //Clear screen
  tft.setCursor(0, 0); //Set upper left corner
  tft.setTextColor(WROVER_WHITE);  //Set text colour
  tft.setTextSize(1); //Set font size
  tft.println("Hello World!"); // Print the text
...

TTGO (aka LILYGO) ESP32 module with integrated e-Paper 2.9-inch display is a robust solution for e-Paper development. Here you will learn basics on handling the e-Paper (e-Ink). The display is two coloured (black/white) with 296×128 pixels resolution. The display is connected and operated via SPI bus
The TTGO T5 module also contains a speaker (buzzer), SPI TF card reader, and a limited GPIO. It is advertised as an electronic badge.

ESP32 provides a number of GPIOs to the developers, but some of them are hard-bound to their features as connected on the development board.

The e-Paper (e-Ink) display is a bi-coloured, 296×128 pixels with SPI interface module, manufactured by Waveshare. It has an integrated SPI controller ³⁾.
There are various software libraries able to handle e-Paper displays but the most advanced one at the moment is GxEPD library that includes device drivers for the majority of manufactured displays Github GxEPD library. The exact model (as to be included in the code is GDEH029A1 https://github.com/lewisxhe/GxEPD/tree/master/src/GxGDEH029A1.

Correct configuration is necessary to build and deploy your code.
For ESP32 TTGO T5 v2.2, a good starting point is the following content for platformio.ini file:

[env:d1_mini]
platform = espressif32
board = esp-wrover-kit
framework = arduino
lib_deps = 
	adafruit/Adafruit-GFX-Library
	Wire
	zinggjm/GxEPD

Write Hello World on the e-Paper screen.
Using e-Paper display and a camera, you can observe it through, are your only interface to the TTGO. Get familiar with handling e-Paper and give it a short practice, as present below.

Type textual “Hello World” on the screen. You're welcome to decorate it, change the size, orientation, experiment with bitmap displaying, partial updates and so on.

To use e-Paper you must include libraries. Beginning of your .cpp source code file should then look more-less following way:

...
#include <Arduino.h>
#include <GxEPD.h>
#include <Adafruit_I2CDevice.h>
#include "SPI.h"
#include <GxIO/GxIO_SPI/GxIO_SPI.h>
#include <GxIO/GxIO.h>
 
//TTGO e-Ink T5 EP32 v 2.2. board specific:
#include <GxGDEH029A1/GxGDEH029A1.h> // 2.9" b/w
#define ELINK_BUSY 4
#define ELINK_RESET 12
#define ELINK_DC 19
#define ELINK_SS 5
 
#define SPI_MOSI 23
#define SPI_MISO 2
#define SPI_CLK 18
...

Note, by the e-Paper related display drivers there is also a font definition library should be included:

...
#include <Fonts/FreeSans9pt7b.h>
...

and then define this font as a default one to use code below:

...
#define DEFALUT_FONT FreeSans9pt7b
...

Then define a controller class that manages your e-Ink display:

...
GxIO_Class io(SPI, ELINK_SS, ELINK_DC, ELINK_RESET);
GxEPD_Class display(io, ELINK_RESET, ELINK_BUSY);
...

Some useful functions to handle e-Paper operations are presented below (but not limited to):

...
  SPI.begin(SPI_CLK, SPI_MISO, SPI_MOSI, -1); 
  display.init();
  display.setRotation(1);
  display.eraseDisplay();
  display.setTextColor(GxEPD_BLACK);
  display.setFont(&DEFALUT_FONT);
  display.setTextSize(0);
 
  display.fillScreen(GxEPD_WHITE);
  display.setCursor(20,20);
  display.println("Hello world");
  display.update();
...

Note, for ease, there are predefined values that present black and white colour display: GxEPD_WHITE and GxEPD_BLACK.

  display.setRotation(1);

PWM is frequently used to control analogue-style, efficient voltage on the GPIO pin. Instead of using resistance driver, PWM uses pulses to change effective power, delivered to the actuator. It applies to motors, but also to LEDs, bulbs, heaters and indirectly to the servos (but that works actually another way, see lectures).
Classical analogWrite method as known from Arduino (Uno, Mega) and ESP8266 does not work here.
ESP32 has sixteen (0 to 15) PWM channels (controllers) that can be freely bound to any of the regular GPIOs.
ESP32 can use various “resolutions” of the PWM: from 8 bit (0..255) to 15bit (0..32767) while regular Arduino uses only 8 bit one.

To use PWM in ESP32 one must perform the following steps:

• Configure GPIO pin as OUTPUT
• Initiate PWM controller with fixing PWM frequency and resolution
• Bind controller to the GPIO pin
• Write to the controller (not to the PIN!) providing duty cycle related to the resolution selected above - every call persistently sets PWM duty cycle until there is the next call to the function setting duty cycle.

In general, you will program using the Arduino framework, remotely via a web interface with the use of the VREL system. Note, your only output is to use the web camera, so results are to be presented this way.
You will also use FreeRTOS functions to handle multicore parallel programming to perform tasks, as presented during the lecture.

Evaluate single-core performance for integer computation. Perform two experiments: with task bound to the APP core and separately to the PRO core. Observe if there is a difference in measurements. Propose an algorithm that is able to generate a complexity of integer computation observable and measurable. Perform at least 10 measurements for each experiment. Consider using parts of code for Dhrystone benchmark https://en.wikipedia.org/wiki/Dhrystone.

Evaluate multi-core performance for integer computation. Perform single-core computation, running at least 4 times (any even number works here) your algorithm. Then execute in parallel (2×2). Observe if there is a difference in measurements. Propose an algorithm that is able to generate a complexity of integer computation observable and measurable. Perform at least 20 measurements for each experiment (10 serial + 10 parallel). Consider using parts of code for Dhrystone benchmark https://en.wikipedia.org/wiki/Dhrystone.

Evaluate single-core performance for floating-point computation. Perform two experiments: with task bound to the APP core and separately to the PRO core. Observe if there is a difference in measurements. Propose an algorithm that is able to generate a complex-enough floating points computation that is observable and measurable. Perform at least 10 measurements for each experiment. Consider using FP parts of code for Whetstone benchmark https://en.wikipedia.org/wiki/Whetstone_(benchmark).

Evaluate multi-core performance for floating-point computation. Perform single-core computation, running at least 4 times (any even number works here) your algorithm. Then execute in parallel (i.e. 2×2). Propose an algorithm that is able to generate a complex-enough floating point computation that is observable and measurable. Perform at least 20 measurements for each experiment (10 serial + 10 parallel). Consider using FP parts of code for Whetstone benchmark https://en.wikipedia.org/wiki/Whetstone_(benchmark).

Include algorithm definition and measurements, along with statistical analysis of the results (at least average and standard deviation) and a summary.

1. ESP32 WROVER kit starting page
2. Hardware definition (pinouts, gpios, etc.)
3. ESP-WROVER-KIT V4.1 schematic
4. https://www.instructables.com/id/Arduino-37-in-1-Sensors-Kit-Explained/Sensor kit
5. https://github.com/LilyGO/TTGO-Electronic-Badge
6. https://github.com/lewisxhe/TTGO-EPaper-Series
7. https://www.waveshare.com/wiki/2.9inch_e-Paper_Module
8. https://github.com/lewisxhe/GxEPD
9. On-line bitmap (image) to memory content (cpp) converter