Introduction

Arduino is a popular open-source hardware platform known for its simplicity, ease of use, and openness. It provides a rich collection of library functions and example code, making it accessible even for individuals without programming experience. Additionally, the Arduino community is highly active, allowing easy access to a wide range of project tutorials, documentation, and support.

Milk-V Duo series now supports Arduino development. You can directly use the Arduino IDE and, after a simple configuration, start using it.

The Duo series CPU adopts a big-little core design, where the Arduino firmware runs on the little core, while the big core is responsible for communication with the Arduino IDE. It receives the Arduino firmware and loads it onto the little core for execution. At the same time, the Linux system in the big core also operates normally.

1. Development Environment Setup

Install Arduino IDE

Arduino IDE supports three operating systems: Windows, Linux, and macOS. According to the system you are using, go to Arduino official website to download the corresponding installation package for installation. The current latest version is 2.3.2, and it is recommended to use version 1.8.X or above.

Add Duo to Arduino IDE

Open Arduino IDE, select Preferences in the File menu, and add the Duo configuration file address in the Additional boards manager URLs in the Settings tab:

https://github.com/milkv-duo/duo-arduino/releases/download/V1.0.0/package_sg200x_index.json

Please download the latest json file address from Releases.

If you have configured other development board addresses before, separate them with commas, or click the icon on the right side of the address bar to bring up the window, and follow the prompts to add them.

After configuring, select Board in the Tools menu, open the Boards Manager, search for SG200X, and click Install.

At this point, the Duo development environment in Arduino IDE has been installed. Now you can write and test the code.

Test blinking the onboard LED

Currently, Duo's SD card system needs to burn firmware that supports Arduino. Please download the firmware with the prefix arduino from Latest Release firmware.

Refer to Boot the Duo in the previous chapter to install the SD card system.

Use a USB cable to connect Duo to your computer, and Duo will automatically power on.

Duo's default firmware, the large-core Linux system, will control the on-board LED flashing. This is achieved through the boot script. Now we are going to use the little-core Arduino to light up the LED. We need to disable the LED flashing script in the large-core Linux. In Duo's Execute in terminal:

mv /mnt/system/blink.sh /mnt/system/blink.sh_backup && sync

That is to say, rename the LED flashing script. After restarting Duo, the LED will no longer flash:

reboot

At this time, there will be an additional serial device in the "Port" of the "Device Manager" of the computer.

On the main interface of Arduino IDE, click Select Board, and then click Select other board and port...

Search for "duo", select Duo Dev Module for Duo, select Duo256 Dev Module for Duo256M, select the corresponding serial port in the port and click OK.

Open the Examples > 01.Basics > Blink test program in the File menu of the Arduino IDE. The function of this program is to blink the onboard LED of the Arduino device. In Duo It is also supported. Let’s just click the Upload button to test:

At this time, you can see the LED on the Duo board blinking at intervals of 1 second.

2. Duo Arduino pin resource

Duo

SPI	PWM	I2C	UART	GPIO	NAME	PIN	PIN	NAME	GPIO	ADC
		I2C0_SCL		1	GP0	1	40	VBUS
		I2C0_SDA		2	GP1	2	39	VSYS
					GND	3	38	GND
	PWM10				GP2	4	37	3V3_EN
	PWM11				GP3	5	36	3V3(OUT)
			UART3_TX		GP4	6	35
			UART3_RX		GP5	7	34
					GND	8	33	GND
SPI2_SCK					GP6	9	32	GP27
SPI2_MOSI					GP7	10	31	GP26		ADC1
SPI2_MISO		I2C1_SDA			GP8	11	30	RUN
SPI2_CSn		I2C1_SCL			GP9	12	29	GP22
					GND	13	28	GND
				14	GP10	14	27	GP21	27
				15	GP11	15	26	GP20	26
					GP12	16	25	GP19	25
					GP13	17	24	GP18	24
					GND	18	23	GND
				19	GP14	19	22	GP17	22
				20	GP15	20	21	GP16	21
				0		LED

Duo256M

SPI	PWM	I2C	UART	GPIO	NAME	PIN	PIN	NAME	GPIO	ADC
				1	GP0	1	40	VBUS
				2	GP1	2	39	VSYS
					GND	3	38	GND
	PWM7				GP2	4	37	3V3_EN
	PWM6				GP3	5	36	3V3(OUT)
			UART3_TX		GP4	6	35
			UART3_RX		GP5	7	34
					GND	8	33	GND
SPI2_SCK		I2C3_SDA			GP6	9	32	GP27
SPI2_MOSI		I2C3_SCL			GP7	10	31	GP26		ADC1
SPI2_MISO		I2C1_SDA			GP8	11	30	RUN
SPI2_CSn		I2C1_SCL			GP9	12	29	GP22
					GND	13	28	GND
		I2C2_SDA		14	GP10	14	27	GP21	27
		I2C2_SCL		15	GP11	15	26	GP20	26
					GP12	16	25	GP19	25
					GP13	17	24	GP18	24
					GND	18	23	GND
				19	GP14	19	22	GP17	22
				20	GP15	20	21	GP16	21
				0		LED

3. Code example

GPIO Usage Example

This program implements Duo physical pin 20 to output high and low levels cyclically with an interval of 1 second, and observe the phenomenon through an external LED.

The connection method is as follows. The negative pole of the LED is connected to the ground of the Duo (for example, pin 18), and the positive pole is connected in series with a 1K resistor and then connected to pin 20:

test code:

#define TEST_PIN 20  //0,1,2,14,15,19,20,21,22,24,25,26,27

// the setup function runs once when you press reset or power the board
void setup() {
  pinMode(TEST_PIN, OUTPUT);
}

// the loop function runs over and over again forever
void loop() {
  digitalWrite(TEST_PIN, HIGH); // turn the TEST_PIN on (HIGH is the voltage level)
  delay(1000);                  // wait for a second
  digitalWrite(TEST_PIN, LOW);  // turn the TEST_PIN off by making the voltage LOW
  delay(1000);                  // wait for a second
}

tip

• If the LED is not connected, you can observe the status changes of the pin through a multimeter or oscilloscope.
• Configuring TEST_PIN to 0 enables testing of the Duo onboard LED.

UART Usage Example

UART Serial port

The UART serial port uses UART3 on physical pin 6/7 by default. When debugging the Arduino program, you can print debugging information through this serial port.

The connection method is as follows. The computer can use a USB to TTL serial port cable. The logic level is 3.3V and the baud rate is 115200. The RX of the serial port cable is connected to the PIN 6 UART3_TX of the Duo. The TX of the serial port cable is connected to the PIN 7 UART3_RX of the Duo. The serial port The GND of the line is connected to any GND of the Duo, such as pin 3:

test code:

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

void loop() {
  Serial.printf("hello world\r\n");
  delay(1000);
}

After running, you can see the "hello world" string printed every 1 second in the computer serial port tool:

hello world
hello world

In addition, the default serial port uses Duo's UART3 interface, so Serial3 can also be used in the program:

void setup() {
  Serial3.begin(115200);
}

void loop() {
  Serial3.printf("hello world\r\n");
  delay(1000);
}

I2C Usage Example

caution

The I2C interface resources of Duo and Duo256M are different and need to be used according to the previous pin resource diagram.

I2C0 sends data to I2C1 (Duo)

The hardware connection is as follows. Connect the SDA and SCL pins of I2C0 and I2C1 correspondingly, and then connect the serial port to the computer to view the printing information according to the method in the UART example above.

The Wire function in Duo is mapped to I2C0 by default, that is, Wire is equivalent to Wire0.

Test code:

#include <Wire.h>

void receive(int a) {
  Serial.printf("receive %d bytes\n\r", a);
  while(a--) {
    Serial.printf("%d \n\r", Wire1.read());
  }
}

void setup() {
  Serial.begin(115200);
  Wire1.begin(0x50);
  Wire1.onReceive(receive);
  Wire.begin();
  Serial.printf("test slave\n\r");
  Wire1.print();
}

byte val = 0;

void loop() {
  Wire.beginTransmission(0x50);         // Transmit to device number 0x50
  Serial.printf("send %d \n\r", ++val);
  Wire.write(val);                      // Sends value byte
  Wire.endTransmission();               // Stop transmitting
  Wire1.onService();
  delay(1000);
}

Test Results:

test slave
Wire1: 1
[iic_dump_register]: ===dump start
IC_CON = 0x22
IC_TAR = 0x55
IC_SAR = 0x50
IC_SS_SCL_HCNT = 0x1ab
IC_SS_SCL_LCNT = 0x1f3
IC_ENABLE = 0x1
IC_STATUS = 0x6
IC_INTR_MASK = 0x224
IC_INTR_STAT = 0
IC_RAW_INTR_STAT = 0x10
[iic_dump_register]: ===dump end
send 1
receive 1 bytes
1
send 2
receive 1 bytes
2
send 3
receive 1 bytes
3
send 4
receive 1 bytes
4

I2C1 sends data to I2C2 (Duo256M)

tip

Note that Duo256M does not have I2C0.

The hardware connection is as follows. Connect the SDA and SCL pins of I2C1 and I2C2 correspondingly, and then connect the serial port to the computer to view the printing information according to the method in the UART example above.

The Wire function in Duo256M is mapped to I2C1 by default, that is, Wire is equivalent to Wire1.

Test code:

#include <Wire.h>

void receive(int a) {
  Serial.printf("receive %d bytes\n\r", a);
  while(a--) {
    Serial.printf("%d \n\r", Wire2.read());
  }
}

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

  Wire2.begin(0x50);
  Wire2.onReceive(receive);

  Wire.begin();
  Serial.printf("test slave\n\r");
  Wire2.print();
}

byte val = 0;

void loop() {
  Wire.beginTransmission(0x50);         // Transmit to device number 0x50
  Serial.printf("send %d \n\r", ++val);
  Wire.write(val);                      // Sends value byte
  Wire.endTransmission();               // Stop transmitting
  Wire2.onService();
  delay(1000);
}

Test Results:

test slave
Wire2: 1
[iic_dump_register]: ===dump start
IC_CON = 0x22
IC_TAR = 0x55
IC_SAR = 0x50
IC_SS_SCL_HCNT = 0x1ab
IC_SS_SCL_LCNT = 0x1f3
IC_ENABLE = 0x1
IC_STATUS = 0x6
IC_INTR_MASK = 0x224
IC_INTR_STAT = 0
IC_RAW_INTR_STAT = 0x10
[iic_dump_register]: ===dump end
send 1
receive 1 bytes
1
send 2
receive 1 bytes
2
send 3
receive 1 bytes
3
send 4
receive 1 bytes
4

SPI Usage Example

SPI loopback test

The hardware connection is as follows. Short-circuit the MOSI and MISO of the SPI, that is, pin 10 and pin 11, and then connect the serial port to the computer according to the method in the UART example above to view the printing information.

Test code:

#include <SPI.h>

char str[]="hello world\n";
void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  SPI.begin();
}

byte i = 0;

void loop() {
  // put your main code here, to run repeatedly:
  // digitalWrite(12, 1);
  SPI.beginTransaction(SPISettings());
  Serial.printf("transfer %c\n\r", str[i]);
  char out = SPI.transfer(str[i++]);        // spi loop back
  SPI.endTransaction();
  Serial.printf("receive %x \n\r", out);
  i %= 12;
}

Test Results:

receive a
transfer h
receive 68
transfer e
receive 65
transfer l
receive 6c
transfer l
receive 6c
transfer o
receive 6f
transfer  
receive 20
transfer w
receive 77
transfer o
receive 6f
transfer r
receive 72
transfer l
receive 6c
transfer d
receive 64
transfer

PWM Usage Example

The hardware connection is as follows. Connect the DUO's GP4 to the negative lead of the LED.

Test code:

void setup() {
  pinMode(6, OUTPUT);
}

void loop() {
  for(int i = 128; i < 255; i++)
  {
    analogWrite(6,i);
    delay(50);
  }
  for(int i = 255; i > 128; i--)
  {
    analogWrite(6,i);
    delay(50);
  }
}

After compiling and burning, you can observe the LED light breathing effect.

ADC Usage Example

The hardware connection is as follows. Connect the GP26 of DUO to the signal pin of the potentiometer, and connect the other two pins to the positive and negative poles of the power supply respectively.

Test code:

int adc_get_val = 0;

void setup() {
  pinMode(0,OUTPUT);
}

void loop() {
  adc_get_val = analogRead(31);

  digitalWrite(0,HIGH);
  delay(adc_get_val);
  digitalWrite(0,LOW);
  delay(adc_get_val);
}

After compiling and burning, you can observe that the flashing frequency of the onboard LED changes as the position of the potentiometer changes.

MailBox Usage Example

Compile and burn the following code into the small core Arduino. This program can read the information sent by the large core from the MailBox and print it to the serial port, for serial port wiring, please refer to the UART Usage Example in this chapter.

#include "mailbox.h"

struct valid_t {
  uint8_t linux_valid;
  uint8_t rtos_valid;
} __attribute__((packed));

typedef union resv_t {
  struct valid_t valid;
  unsigned short mstime;  // 0 : noblock, -1 : block infinite
} resv_t;

typedef struct cmdqu_t cmdqu_t;
/* cmdqu size should be 8 bytes because of mailbox buffer size */
struct cmdqu_t {
  uint8_t ip_id;
  uint8_t cmd_id : 7;
  uint8_t block : 1;
  union resv_t resv;
  unsigned int param_ptr;
} __attribute__((packed)) __attribute__((aligned(0x8)));

void showmsg(MailboxMsg msg) {
  cmdqu_t *cmdq;
  Serial.print("Get Msg: ");
  Serial.println(*(msg.data), HEX);
  cmdq = (cmdqu_t *)msg.data;
  Serial.printf("cmdq->ip_id = %d\r\n", cmdq->ip_id);
  Serial.printf("cmdq->cmd_id = %x\r\n", cmdq->cmd_id);
  Serial.printf("cmdq->block = %d\r\n", cmdq->block);
  Serial.printf("cmdq->para_ptr = %x\r\n", cmdq->param_ptr);
  *(msg.data) = 0;
}

void setup() {
  Serial.begin(115200);
  mailbox_init(false);
  mailbox_register(0, showmsg);
  mailbox_enable_receive(0);
  Serial.println("Mailbox Start");
}

void loop() {
  
}

Compile the test program mailbox_test and run it on large-core Linux. The test program has been stored in the duo-examples warehouse. You can refer to README for compilation.

After running, the big core Linux output：

C906B: cmd.param_ptr = 0x2
C906B: cmd.param_ptr = 0x3

Small core serial port printing：

Mailbox Start
Get Msg: 19300
cmdq->ip_id = 0
cmdq->cmd_id = 13
cmdq->block = 1
cmdq->para_ptr = 2
Get Msg: 19300
cmdq->ip_id = 0
cmdq->cmd_id = 13
cmdq->block = 1
cmdq->para_ptr = 3

4. Demo and Projects

Coming Soon ...

5. Arduino APIs

Digital I/O

digitalWrite()

void digitalWrite(uint8_t pinNumber, uint8_t status)

Write a HIGH or a LOW value to a digital pin.

digitalRead()

int digitalRead(uint8_t pinNumber)

Reads the value from a specified digital pin, either HIGH or LOW.

pinMode()

void pinMode(uint8_t pinNumber, uint8_t pinMode)

Configures the specified pin to behave either as an input or an output

Analog I/O

analogRead()

uint32_t analogRead(uint32_t pinNumber)

Reads the value from the specified analog pin.

analogReadResolution()

void analogReadResolution(int bits)

Sets the size (in bits) of the value returned by analogRead().

analogWrite()

void analogWrite(uint8_t pinNumber, uint32_t val)

Writes an analog value (PWM wave) to a pin.

analogWriteResolution()

void analogWriteResolution(int bits)

analogWriteResolution() sets the resolution of the analogWrite() function.

Wire(I2C)

begin()

void begin(csi_iic_addr_mode_t addr_mode = IIC_ADDRESS_7BIT);
void begin(uint16_t address, csi_iic_addr_mode_t addr_mode = IIC_ADDRESS_7BIT);

beginTransmission()

void beginTransmission(uint16_t);

endTransmission()

uint8_t endTransmission(bool stopBit);
uint8_t endTransmission(void);

requestFrom()

size_t requestFrom(uint16_t address, size_t quantity, bool stopBit);
size_t requestFrom(uint16_t address, size_t quantity);

write()

size_t write(uint8_t data);
size_t write(const uint8_t * data, size_t quantity);

available()

virtual int available(void);

read()

virtual int read(void);

onReceive()

void onReceive(void(*)(int));

onRequest()

void onRequest(void(*)(void));

Other functional interfaces and their usage in Duo will be updated in the future. You can also refer to Arduino official documentation first.