Embedded Programming

This week, I learned embedded programming.wow ! it felt like deciphering an ancient script, with everything being new acquaintances. After going through a lot of materials, I finally gained some understanding of the programming architecture. In the end, I achieved a little interaction and communication, and it feels really rewarding!

1.1 Assignments of the Week

• Group assignment:

Browse through the datasheet for your microcontroller

Compare the performance and development workflows for other architectures

• Individual assignment:

Write a program for a microcontroller development board to interact (with local input &/or output devices) and communicate (with remote wired or wireless devices)

1.2 Group Work

We tried to use Arduino Uno, Mirco-Bit...... Here is the documentation.

1.3 Individual Work

The individual assignment requires using microcontroller development boards to write programs for interact and communicate.It's really fascinating!

1.3.1 interact (with local input &/or output devices)

• (1) Microbit



I want to create a 123 numbers melody using the three digital pins and the 5x5 LED matrix on microbit. The desired outcome is that when I touch a pin, the corresponding number LED should light up. Let's work on this together!

1.Open the web version of MakeCode, and a delightful and charming interface will appear. Begin a new project.



2.Basic—On start—Show string"Hello!"

3.Input—On pin(Pin)pressed,when a pin is touched and released again(while also touching the GND pin).

4.Basic—show leds,click on the block to set the LED positions.



5.This is the complete code block. You can test it online in the web browser. It works perfectly and achieves the desired effect!



6.Click on download and select your connected device.



Look!

• (2) Seeed XIAO RP2040

Utilizing the pre-mill PCB board, create an input-output interactive device with the buttons(GPIO Pin 27) and three small LEDs(GPIO Pin 27/0/1). The basic idea is to press the button (high-level signal), and three small LEDs sequentially light up at a speed of 0.5 seconds, then return to the low-level signal.



Configure button and LED pins based on the pin diagram above. Set the button as input and the LED as output. Use IF statements to control the states of high and low levels.

Coding-Wire Sample code:

int button = 27; // button link D1 int led1 = 26; // the frist light link D0 int led2 = 0; // the seconed light link D6 int led3 = 1; // the third light link D7 void setup() { pinMode(button, INPUT); pinMode(led1, OUTPUT); pinMode(led2, OUTPUT); pinMode(led3, OUTPUT); } void loop() { int state = digitalRead(button); if (state == HIGH) { digitalWrite(led1, HIGH); delay(500); digitalWrite(led2, HIGH); delay(500); digitalWrite(led3, HIGH); delay(500); } else{ digitalWrite(led1, LOW); digitalWrite(led2, LOW); digitalWrite(led3, LOW); } }









Look!

1.3.2 Serial Communication

• (1) Seeed XIAO RP2040 (Board and computer communication)

I did inter-board communication for the first time, so I first learned about serial communication between boards and computers. In the Arduino IDE, I connected the Seeed XIAO RP2040 development board and implemented two simple communications.

1.Through the serial port, it sends the string "Hi! Juliet" once per second. When you connect Arduino to the computer and open the Serial Monitor in the Arduino IDE, you can see the "Hi! Juliet" string scrolling automatically every second.

viod setup() Serial.begin(9600); viod loop(){ println("Hi!Juliet"); delay(1000); }










2.In the advanced version below, send data to Arduino through the Serial Monitor, and you should see the same data being sent back in the monitor. This type of program is very useful for debugging serial communication (testing if serial communication is working properly).

viod setup() Serial.begin(9600); viod loop(){ while(Serial.available()>0{ char c=Serial.read(); Serial.write(c); } }










• (2) Board-to-board communication:

When I wanted to connect with another board, I found that the Seeed Xiao RP2040 has only one physical TX (transmit) and RX (receive) pin for serial communication, and the interface is connected to the computer's USB port. This means I cannot directly use UART communication. So, I decided to use I2C! (Later, I found out it's not the case, and UART can be used. Please see the group assignment for the process and reasons!)

However! I sadly discovered that the PCB I milled using CNC last time does not support the pins I need to use! So, I tried connecting it to another Arduino Uno on a breadboard.

Before this, what is I2C and SPI?

I2C: It is a bidirectional, half-duplex serial communication protocol developed by Philips (now NXP). It only requires two lines, SDA (data line), and SCL (clock line). I2C supports Multi-Mastering mode, where any device capable of sending and receiving can become a master, controlling data transmission and clock frequency. In general, I2C is more suitable for low-speed, multi-master, and simple connection scenarios.

SPI: It is a synchronous serial communication protocol supporting point-to-point and multi-point communication. The SPI bus typically uses four lines: SCLK (clock), MOSI (Master Out Slave In), MISO (Master In Slave Out), and SS (Slave Select). However, some implementations use only three lines. Overall, SPI is more suitable for high-speed, point-to-point, or multi-point communication scenarios.

Next is my I2C journey:Open Arduino IDE—Select Seeed XIAO RP2040 board(Arduino UNO)—File—Examples—Wire—TalkingToMyself, I obtained a sample code from Arduino IDE, which helped me gain a better understanding of I2C.



Coding-Wire Sample code:

#include <Wire.h> void setup() { Serial.begin(115200); delay(5000); Wire.setSDA(0); Wire.setSCL(1); Wire.begin(); Wire1.setSDA(2); Wire1.setSCL(3); Wire1.begin(0x30); Wire1.onReceive(recv); Wire1.onRequest(req); } static char buff[100]; void loop() { static int p; char b[90]; // Write a value over I2C to the slave Serial.println("Sending..."); Wire.beginTransmission(0x30); sprintf(b, "pass %d", p++); Wire.write(b, strlen(b)); Wire.endTransmission(); // Ensure the slave processing is done and print it out delay(1000); Serial.printf("buff: '%s'\r\n", buff); // Read from the slave and print out Wire.requestFrom(0x30, 6); Serial.print("\nrecv: '"); while (Wire.available()) { Serial.print((char)Wire.read()); } Serial.println("'"); delay(1000); } // These are called in an **INTERRUPT CONTEXT** which means NO serial port // access (i.e. Serial.print is illegal) and no memory allocations, etc. // Called when the I2C slave gets written to void recv(int len) { int i; // Just stuff the sent bytes into a global the main routine can pick up and use for (i = 0; i < len; i++) { buff[i] = Wire1.read(); } buff[i] = 0; } // Called when the I2C slave is read from void req() { static int ctr = 765; char buff[7]; // Return a simple incrementing hex value sprintf(buff, "%06X", (ctr++) % 65535); Wire1.write(buff, 6); }








Here, I'm Master, my friend is Slave. We use the Wire library for I2C communication with a slave address of 8. The slave device waits for commands from the master device. The master device sends various commands to the slave device through I2C, including inquiries about the number of characters, reading available data, and sending data after reading.

Coding-I2C Master:

#include <Wire.h> String msg = ""; String input = ""; int mode; void recv(int count) { char c = Wire.read(); if (c == 0) { mode = 0; } else if (c == 1) { mode = 1; } else if (c == 2) { while (Wire.available() > 0) { char c = Wire.read(); Serial.write(c); } } } void req() { if (mode == 0) { Wire.write(msg.length()); } else if (mode == 1) { Wire.write(msg.c_str(), msg.length()); msg = ""; } } void setup() { Serial.begin(9600); Wire.begin(8); Wire.onReceive(recv); Wire.onRequest(req); } void loop() { while (Serial.available() > 0) { char c = Serial.read(); msg += c; input += c; if (c == '\n') { Serial.print("me: "); Serial.print(input); input = ""; } } }








Coding-I2C Slave:

#include <Wire.h> String input = ""; void setup() { Wire.begin(); Serial.begin(9600); } void loop() { Wire.beginTransmission(8); Wire.write(0); Wire.endTransmission(); int l = Wire.requestFrom(8, 1); if (l == 1) { char n = Wire.read(); if (n > 0) { Wire.beginTransmission(8); Wire.write(1); Wire.endTransmission(); Wire.requestFrom(8, n); while (Wire.available()) { char c = Wire.read(); Serial.print(c); } } } if (Serial.available() > 0) { Wire.beginTransmission(8); Wire.write(2); while (Serial.available() > 0) { char c = Serial.read(); Wire.write(c); input += c; if (c == '\n') { Serial.print("me:"); Serial.print(input); input = ""; } } Wire.endTransmission(); } }








After verifying the code, unloading, and then connecting, both sides couldn't receive each other's messages. After thoroughly checking the code, no issues were found. Later, it was discovered that the problem was due to the lack of a GND connection.



Details of the wiring diagram.



After identifying the cause, the Serial Monitor successfully received messages from the other side! Hooray!

1.4 All files

I2C Master

I2C Slave

interact