Mraa 使用

MRAA 简介

Eclipse Mraa（Libmraa）是一个包含 Java、Python 和 JavaScript 绑定的 C/C++ 库，用于连接各种物联网和边缘平台上的 I/O 引脚和总线，其 API 结构合理，端口名称/编号与所在的电路板相匹配。

安装 MRAA

sudo apt-get update -y
sudo apt-get install libmraa2 libmraa-dev libmraa-java python3-mraa mraa-tools -y

MRAA 命令行工具

GPIO

mraa-gpio list：列出所有可用引脚
mraa-gpio get pin：获取引脚状态
mraa-gpio set pin level：设置引脚状态
mraa-gpio version：获取版本信息

I2C

mraa-i2c list：列出所有可用 I2C 总线
mraa-i2c version：获取 mraa 版本和板卡名称
mraa-i2c detect bus：列出指定总线上检测到的设备
mraa-i2c get bus device reg：从指定设备寄存器中获取值
mraa-i2c set bus device reg value：将指定设备寄存器设置为值

UART

mraa-uart list：列出所有可用 UART 端口
mraa-uart dev dev_num baud customized_baud send str: 将字符串 str 发送到指定端口
mraa-uart dev dev_num baud customized_baud recv 1000：读取端口 dev_num 上的数据，最多读取 1000 字节，并将它们显示在 stdout 上

示例代码

GPIO

C
Python

blink.c

#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include "mraa/gpio.h"

/* gpio declaration */
#define GPIO_PIN 3

volatile sig_atomic_t flag = 1;

void sig_handler(int signum) {
    if(signum == SIGINT) {
        fprintf(stdout, "Exiting...\n");
        flag = 0;
    }
}

int main(void) {
    mraa_result_t status = MRAA_SUCCESS;
    mraa_gpio_context gpio;

    signal(SIGINT, sig_handler);

    mraa_init();

    /* initialize GPIO */
    gpio = mraa_gpio_init(GPIO_PIN);
    if(gpio == NULL) {
        fprintf(stderr, "Failed to initialize GPIO %d\n", GPIO_PIN);
        mraa_deinit();
        return EXIT_FAILURE;
    }

    /* set output */
    status = mraa_gpio_dir(gpio, MRAA_GPIO_OUT);
    if(status != MRAA_SUCCESS) {
        goto err_exit;
    }

    while(flag) {
        status = mraa_gpio_write(gpio, 1);
        if(status != MRAA_SUCCESS) {
            goto err_exit;
        }
        sleep(1);

        status = mraa_gpio_write(gpio, 0);
        if(status != MRAA_SUCCESS) {
            goto err_exit;
        }

        sleep(1);
    }

    /* release gpio's */
    status = mraa_gpio_close(gpio);
    if(status != MRAA_SUCCESS) {
        goto err_exit;
    }

    mraa_deinit();

    return EXIT_SUCCESS;

err_exit:
    mraa_result_print(status);

    mraa_deinit();

    return EXIT_FAILURE;
}

使用方法：

将 led 信号脚连接到 PIN3，VCC 接板子 VCC，GND 接板子 GND
测试

gcc blink.c -lmraa -o blink && sudo ./blink

若测试成功，led 会有一个闪烁的效果。

blink.py

#!/usr/bin/env python3
# -*- encoding: utf-8 -*-

import mraa
import time

pin = 3  # set pin num

try:
    gpio = mraa.Gpio(pin)
    gpio.dir(mraa.DIR_OUT)  # set mode as input

    while True:
        gpio.write(1)
        time.sleep(1)
        gpio.write(0)
        time.sleep(1)

except KeyboardInterrupt:
    print("\nstop\n")

使用方法：

将 led 信号脚连接到 PIN3，VCC 接板子 VCC，GND 接板子 GND
测试

sudo python3 Blink.py

若测试成功，led 会有一个闪烁的效果。

I2C

C
Python

led_i2c_blink.c

#include <math.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include "mraa/i2c.h"

#define I2C_BUS 2
#define LED_ADDRESS 0x20

volatile sig_atomic_t flag = 1;

void sig_handler(int signum) {
	if (signum == SIGINT) {
		fprintf(stdout, "Exiting...\n");
		flag = 0;
	}
}

int main() {
	mraa_result_t status = MRAA_SUCCESS;
	mraa_i2c_context i2c;

	signal(SIGINT, sig_handler);
	mraa_init();

	i2c = mraa_i2c_init(I2C_BUS);
	if(i2c == NULL) {
		fprintf(stderr, "Failed to initialize I2C\n");
		mraa_deinit();
		return EXIT_FAILURE;
	}

	/* set slave address */
	status = mraa_i2c_address(i2c, LED_ADDRESS);
	if(status != MRAA_SUCCESS) {
		return -1;
	}

	while(1) {
		/**
		 * Write a single word to an i2c context
		 *
		 * @param dev The i2c context
		 * @param data The word to write
		 * @param command The register
		 * @return Result of operation
		 */
		mraa_i2c_write_byte_data(i2c, 0x23, 0x08);
		sleep(1);
		mraa_i2c_write_byte_data(i2c, 0x21, 0x01);
		sleep(1);
		mraa_i2c_write_byte_data(i2c, 0x33, 0x12);
		sleep(1);
		mraa_i2c_write_byte_data(i2c, 0x1f, 0x42);
		sleep(1);
	}

	return 0;
}

使用方法：

打开 I2C2 的 Overlay，并重启
接线： SDA <--> SDA, SCL <--> SCL, GDN <--> GND, VCC <--> VCC
打开终端，输入以下命令进行测试

gcc led_i2c_blink.c -lmraa -o led_i2c_blink && sudo ./led_i2c_blink

若测试成功， I2C Led 会有一个流水灯效果。

led_i2c_blink.py

#!/usr/bin/env python3
# -*- encoding: utf-8 -*-

import mraa
import time

# initialise I2C
x = mraa.I2c(2)
x.address(0x20)

while True:
	x.writeReg(0x11, 0x01)
	time.sleep(0.5)
	x.writeReg(0x12, 0x02)
	time.sleep(0.5)
	x.writeReg(0x13, 0x03)
	time.sleep(0.5)
	x.writeReg(0x14, 0x04)
	time.sleep(0.5)
	x.writeReg(0x15, 0x05)
	time.sleep(0.5)
	x.writeReg(0x16, 0x06)

使用方法：

打开 I2C2 的 Overlay，并重启
接线： SDA <--> SDA, SCL <--> SCL, GDN <--> GND, VCC <--> VCC
打开终端，输入以下命令进行测试

sudo python3 led_i2c_blink.py

PWM

C
Python

led_pwm_fade_out.c

#include <signal.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include "mraa/pwm.h"

/* PWM period in us */
#define PWM_FREQ 1e3

char *usage =
	"Usage: %s pwm_pin\n"
	"Example: %s 3\n";

int main(int argc, char *argv[]) {
	char usagestr[130];
	char *str = NULL;
	int invalid = 0, pwm_num = 0;
	mraa_result_t status = MRAA_SUCCESS;
	mraa_pwm_context pwm;
	float output = 0.0;
	float duty_cycle = 0.0;
	float step = 0.05;

	memset(usagestr, '\0', 130);
	// expect only 1 argument => argc must be 2
	if(argc != 2) {
		snprintf(usagestr, 129, usage, argv[0], argv[0]);
		puts(usagestr);
		return -1;
	}
	// check for a valid, numeric argument
	str = argv[1];
	while(*str != '\0') {
		if(!isdigit(*str)) {
			invalid = 1;
		}
		str++;
	}
	if(invalid == 1) {
		printf("%s: Invalid GPIO %s\n", argv[0], argv[2]);
		return -1;
	}
	pwm_num = atoi(argv[1]);

	mraa_init();

	/* init pwm */
	if((pwm = mraa_pwm_init(pwm_num)) == NULL) {
		printf("Failed to initialize PWM\n");
		mraa_deinit();
		return -1;
	}
	/* set period */
	if((status = mraa_pwm_period_us(pwm, PWM_FREQ))) {
		printf("Failed to set pwm period\n");
		return -1;
	}
	/* enable pwm */
	if((status = mraa_pwm_enable(pwm, 1)) != MRAA_SUCCESS) {
		printf("Failed to Enable PWM\n");
		return -1;
	}

	while (1) {
		// Set pwm duty cycle
		mraa_pwm_write(pwm, duty_cycle);

		// sleep 100 ms
		usleep(100000);

		// change the duty cycle
		duty_cycle += step;
		if (duty_cycle > 1.0) {
			duty_cycle = 0.0;
		}

		printf("PWM value: %f\n", mraa_pwm_read(pwm));
	}

	mraa_pwm_close(pwm);

	return 0;
}

使用方法：

打开某个 PIN 的 PWM Overlay，并重启，这里以 PIN28 的 PWM 为例
将 led 的信号引脚接 PIN28 引脚，VCC 接板子 VCC， GDN 接板子 GND
测试

gcc led_pwm_fade_out.c -lmraa -o led_pwm_fade_out && sudo ./led_pwm_fade_out 28

若测试成功，led 会有一个呼吸灯的效果。

led_pwm_fade_out.py

#!/usr/bin/env python
# -*- encoding: utf-8 -*-

import mraa
import time

class Led_pwm_fade_out:
    def __init__(self, pwm_pin):
        self.pwm_pin = pwm_pin
        self.pwm = mraa.Pwm(pwm_pin)
        self.duty_cycle = 0.0
        self.pwm_freq = 1e3
        self.pwm_step = 0.05

    def initialize(self):
        if self.pwm == None:
            exit()

        if self.pwm.period_us(self.pwm_freq) != mraa.SUCCESS:
            mraa.Pwm.close()
            exit()

        if self.pwm.enable(True) != mraa.SUCCESS:
            mraa.Pwm.close()
            exit()

    def set_duty_cycle(self, duty_cycle):
        self.duty_cycle = duty_cycle
        self.pwm.write(duty_cycle)

    def run(self):
        try:
            while True:
                self.set_duty_cycle(self.duty_cycle)
                self.duty_cycle += self.pwm_step
                if self.duty_cycle > 1.0:
                    self.duty_cycle = 0.0
                print("0x%x\n" %self.pwm.read(self.pwm))
                time.sleep(1)

        except:
            print("Error")

        finally:
            self.pwm.write(0)  # Stop PWM
            self.pwm.disable()  # Disable PWM
            self.pwm.close()  # Close PWM

if __name__ == '__main__':

    pwm_controller = Led_pwm_fade_out(28)

    pwm_controller.initialize()

    pwm_controller.run()

使用方法：

打开某个 PIN 的 PWM Overlay，并重启，这里以 PIN28 的 PWM 为例
将 led 的信号引脚接 PIN28 引脚，VCC 接板子 VCC， GDN 接板子 GND
测试

sudo python3 Led_pwm_fade_out.py

若测试成功，led 会有一个呼吸灯的效果。

SPI

C
Python

spi_test.c

#include <signal.h>
#include <stdlib.h>
#include <unistd.h>

/* mraa header */
#include "mraa/spi.h"

/* SPI declaration */
#define SPI_BUS 0

/* SPI frequency in Hz */
#define SPI_FREQ 400000

int main(int argc, char** argv) {
	mraa_result_t status = MRAA_SUCCESS;
	mraa_spi_context spi;
	int i, j;

	/* initialize mraa for the platform (not needed most of the times) */
	mraa_init();

	//! [Interesting]
	/* initialize SPI bus */
	spi = mraa_spi_init(SPI_BUS);
	if (spi == NULL) {
		fprintf(stderr, "Failed to initialize SPI\n");
		mraa_deinit();
		return EXIT_FAILURE;
	}

	/* set SPI frequency */
	status = mraa_spi_frequency(spi, SPI_FREQ);
	if (status != MRAA_SUCCESS)
		goto err_exit;
	/* set big endian mode */
	status = mraa_spi_lsbmode(spi, 0);
	if (status != MRAA_SUCCESS) {
		goto err_exit;
	}

	while(1) {
		printf("0x%x\n",mraa_spi_write(spi, 0xaa));
		sleep(1);
	}
err_exit:
	mraa_result_print(status);

	/* stop spi */
	mraa_spi_stop(spi);

	/* deinitialize mraa for the platform (not needed most of the times) */
	 mraa_deinit();

	return EXIT_FAILURE;
}

使用方法：

打开 spi0 即 spidev0.0 的 Overlay，并重启
测试

打开终端，分别输入以下命令进行测试

gcc spi_test.c -o spi_test && sudo ./spi_test

若测试成功，终端会输出 "0xaa"

Spi_test.py

#!/usr/bin/env python
# -*- encoding: utf-8 -*-

import mraa
import time

class Spi_test:
    def __init__(self, spi_index):
        self.spidev = mraa.Spi(spi_index)
        self.freq = 400000

    def initialize(self):
        if self.spidev.frequency(self.freq) != mraa.SUCCESS:
            exit()

        if self.spidev.lsbmode(False) != mraa.SUCCESS:
            exit()

    def write_byte(self, value):
        return self.spidev.writeByte(value)

    def close(self):
        self.close()


if __name__ == '__main__':
    # create spi device
    spi_device = Spi_test(0)

    # init
    spi_device.initialize()

    try:
        while True:
            # value = ...
            print("0x%x\n" % spi_device.write_byte(0xaa))
            time.sleep(1)
    except:
        print("Error")
    finally:
        spi_device.close()

使用方法：

打开 spi0 即 spidev0.0 的 Overlay，并重启
测试

打开终端，分别输入以下命令进行测试

sudo python3 Spi_test.py

若测试成功，终端会输出 "0xaa"

UART

C
Python

snd.c

#include <signal.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include "mraa/uart.h"

#ifndef FALSE
#define FALSE 0
#define TRUE (!FALSE)
#endif

char *usage =
	"Usage: %s uart_path_id msg\n"
	"Example: %s 4 'this is test message'\n";

int main(int argc, char *argv[]) {
	char usagestr[130];
	char *str = NULL;
	int invalid = 0;
	mraa_uart_context snd_uart;
	mraa_result_t status = MRAA_SUCCESS;

	memset(usagestr, '\0', 130);
	if(argc != 3) {
		snprintf(usagestr, 129, usage, argv[0], argv[0]);
		puts(usagestr);
		return -1;
	}

	mraa_init();

    char uart_path[15];
    snprintf(uart_path, sizeof(uart_path), "/dev/ttyS%d", atoi(argv[1]));
	printf("uart_path: %s, msg: %s\n", uart_path, argv[2]);

	if((snd_uart = mraa_uart_init_raw(uart_path)) == NULL) {
		printf("Failed to initialize UART\n");
		mraa_deinit();
		return -1;
	}

    if ((status = mraa_uart_set_baudrate(snd_uart, 115200)) != MRAA_SUCCESS) {
        return -1;
    }

    if ((status = mraa_uart_set_mode(snd_uart, 8, MRAA_UART_PARITY_NONE, 1)) != MRAA_SUCCESS) {
        return -1;
    }

    if ((status = mraa_uart_set_flowcontrol(snd_uart, FALSE, FALSE)) != MRAA_SUCCESS) {
        return -1;
    }

	while(1) {
		mraa_uart_write(snd_uart, argv[2], strlen(argv[2]));
		sleep(1);
	}

	mraa_uart_stop(snd_uart);
	mraa_deinit();

	return 0;
}

recv.c

#include <signal.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include "mraa/uart.h"

#ifndef FALSE
#define FALSE 0
#define TRUE (!FALSE)
#endif

char *usage =
	"Usage: %s uart_path_id\n"
	"Example: %s 4\n";


int main(int argc, char *argv[]) {
	char usagestr[130];
	char *str = NULL;
	int invalid = 0, uart_id = 0;
	mraa_uart_context recv_uart;
	mraa_result_t status = MRAA_SUCCESS;

	memset(usagestr, '\0', 130);
	if(argc != 2) {
		snprintf(usagestr, 129, usage, argv[0], argv[0]);
		puts(usagestr);
		return -1;
	}
	// check for a valid, numeric argument
	str = argv[1];
	while(*str != '\0') {
		if(!isdigit(*str)) {
			invalid = 1;
		}
		str++;
	}
	if(invalid == 1) {
		printf("%s: Invalid GPIO %s\n", argv[0], argv[1]);
		return -1;
	}

	mraa_init();

	char uart_path[15];
	snprintf(uart_path, sizeof(uart_path), "/dev/ttyS%d", atoi(argv[1]));
	printf("uart_path: %s\n", uart_path);

	if((recv_uart = mraa_uart_init_raw(uart_path)) == NULL) {
		printf("Failed to initialize UART\n");
		mraa_deinit();
		return -1;
	}

	if ((status = mraa_uart_set_baudrate(recv_uart, 115200)) != MRAA_SUCCESS) {
		return -1;
	}

	if ((status = mraa_uart_set_mode(recv_uart, 8, MRAA_UART_PARITY_NONE, 1)) != MRAA_SUCCESS) {
		return -1;
	}

	if ((status = mraa_uart_set_flowcontrol(recv_uart, FALSE, FALSE)) != MRAA_SUCCESS) {
		return -1;
	}

	char recv_buff[1024];
	while(1) {
		if (mraa_uart_data_available(recv_uart, 1) == TRUE) {
			mraa_uart_read(recv_uart, recv_buff, sizeof(recv_buff));
			printf("recv: %s\n", recv_buff);
			sleep(1);
		}
	}
}

使用方法：

打开两个 UART 的 Overlay，这里以 uart4 和 uart6 即 /dev/ttyS4 和 /dev/ttyS6 为例
连个 UART 的 TX RX 引脚交叉接线
测试

打开两个终端，分别输入以下命令进行测试

gcc recv.c -lmraa -o recv && sudo ./recv 6 # /dev/ttyS6

gcc snd.c -lmraa -o  snd && sudo ./snd 4 "hello, this is test"  # /dev/ttyS4

若测试成功， uart6 会接收到来自 uart4 发送的循环消息 "hello, this is test"

Snd.py

#!/usr/bin/env python
# -*- encoding: utf-8 -*-

import mraa
import time

class Snd:

	def __init__(self, uart_id, baurd_rate, parity, stopbits):
		self.uart_id = uart_id
		self.uart_snd = mraa.Uart(uart_id)
		self.uart_snd.setBaudRate(baurd_rate)
		self.uart_snd.setMode(parity, mraa.UART_PARITY_NONE, stopbits)
		self.uart_snd.setFlowcontrol(False, False)

	def send_message(self, message):
		snd_msg = bytearray(message, "ascii")
		self.uart_snd.write(snd_msg)
		self.uart_snd.flush()

if __name__ == '__main__':
	# init uart
	uart_snd =  Snd(1, 115200, 8, 1)

	while True:
		uart_snd.send_message("Hello, this is snd side.\n")
		time.sleep(1)

Recv.py

#!/usr/bin/env python
# -*- encoding: utf-8 -*-

import mraa
import time
import sys

class Recv:
	def __init__(self, uart_id, baurd_rate, parity, stopbits):
		self.uart_id = uart_id
		self.baurd_rate = baurd_rate
		self.parity = parity
		self.stopbits = stopbits
		self.uart = mraa.Uart(uart_id)
		self.initialize_uart()

	def initialize_uart(self):
		self.uart.setBaudRate(self.baurd_rate)
		self.uart.setMode(self.parity, mraa.UART_PARITY_NONE, self.stopbits)
		self.uart.setFlowcontrol(False, False)

	def run(self):
		try:
			while True:
				if self.uart.dataAvailable():
					data_byte = self.uart.readStr(125)
					print(data_byte)

					# Just a two-way half-duplex communication example, "X" is a flag
					if data_byte == "X":
						self.uart.writeStr("Yes, master!")

		except KeyboardInterrupt:
			print("Exiting...")
			self.uart.writeStr("Exiting...")
			self.uart.close()
			sys.exit()

if __name__ == '__main__':

	uart_receiver = Recv(2, 115200, 8, 1)

	uart_receiver.run()

使用方法：

打开两个 UART 的 Overlay，这里以 uart4 和 uart6 即 /dev/ttyS4 和 /dev/ttyS6 为例
连个 UART 的 TX RX 引脚交叉接线
测试

打开两个终端，分别输入以下命令进行测试

sudo python3 Recv.py

sudo python3 Snd.py

若测试成功， uart6 会接收到来自 uart4 发送的循环消息 "Hello, this is snd side."

Mraa 使用

MRAA 简介

安装 MRAA​

MRAA 命令行工具​

GPIO​

I2C​

UART​

示例代码​

GPIO​

I2C​

PWM​

SPI​

UART​

参考​

安装 MRAA

MRAA 命令行工具

GPIO

I2C

UART

示例代码

GPIO

I2C

PWM

SPI

UART

参考