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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
  • 卸载系统原装的包:
cd /
sudo apt purge *mraa*
  • 源码安装

sudo apt-get update -y
sudo apt-get install git cmake build-essential swig4.0 python-dev python3-dev libnode-dev  cmake libjson-c-dev libgtest-dev pkg-config cmake-data -y
git clone https://github.com/nascs/mraa.git
cd mraa
git checkout -b undefined origin/undefined
mkdir build && cd build
cmake .. && make -j${nproc} && sudo make install && sudo ldconfig

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

asciicast

mraa-uart 使用例子

示例代码​

GPIO​

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。

I2C​

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。

PWM​

注意

由于 pwmchip 驱动的改动，MRAA 的 PWM 功能在 6.1 内核上无法正常工作

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。

SPI​

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"

UART​

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"

参考​