Linux 设备驱动 -- SPI子系统

OLED显示模块

• 0.96寸
• 分辨率128 x 64
• 使用驱动芯片SSD1306
• 支持I2C、4线SPI、3线SPI接口

OLED模块硬件接口具有6个引脚：

• VCC
• GND
• SCL，无论是SPI还是I2C接口时，它都是始终引脚
• SDA，当使用I2C接口，它是I2C的SDA，当使用SPI，它是MOSI
• RST，复位引脚
• DC，命令数据选择引脚
• 当DC引脚拉低，表示写入的是命令
• 当DC引脚拉高，表示写入的是数据

注意事项：

OLED 显示屏不同于 LCD，OLED 上电是没有反应的，需要程序驱动才会有显示！

具体如何编程查看SSD1306芯片手册

设备树

OLED驱动实现

1、OLED硬件操作

spi写操作：

staticintoled_spi_write(char *buf, uint16_t len){int status;#if 0structspi_messagemsg;structspi_transferxfer = {        .len = len,        .tx_buf = buf,    };    spi_message_init(&msg);                       /* 初始化spi_message */    spi_message_add_tail(&xfer, &msg);             /* 添加到传输队列 */    status = spi_sync(oled_dev->spi, &msg);          /* 同步发送 */#else    status = spi_write(oled_dev->spi, buf, len);   #endifreturn status;}

• spi_write，封装了spi_message_init、spi_message_add_tail和spi_sync步骤

OLED写操作：

enum {    OLED_CMD = 0x00,    OLED_DATA = 0x01,};typedefunsignedcharoled_cmd_t;staticintoled_write_cmd_data(uint8_t data, oled_cmd_t cmd){int ret = 0;if (cmd == OLED_CMD)        gpio_set_value(oled_dev->dc_gpio, OLED_CMD); /* 拉低，表示写入的是指令 */else        gpio_set_value(oled_dev->dc_gpio, OLED_DATA); /* 拉高，表示写入数据 */    ret = oled_spi_write(&data, sizeof(data));return ret;}staticintoled_write_datas(uint8_t *datas, uint16_t len){int ret = 0;    gpio_set_value(oled_dev->dc_gpio, OLED_DATA);    ret = oled_spi_write(datas, len);return ret;}

设置OLED显示坐标：

staticintoled_set_pos(uint16_t x, uint16_t y){int ret = 0;    ret = oled_write_cmd_data(0xb0 + y, OLED_CMD);    ret = oled_write_cmd_data((x & 0x0f), OLED_CMD);    ret = oled_write_cmd_data(((x & 0xf0) >> 4) | 0x10, OLED_CMD);return ret;}

OLED复位 ：

staticvoidoled_set_rst(uint8_t on_off){    gpio_set_value(oled_dev->rst_gpio, on_off);}staticvoidoled_reset(void){    oled_set_rst(0);    mdelay(50);    oled_set_rst(1);}

OLED显示开关：

staticvoidoled_disp_on_off(uint8_t on_off){if (on_off)        oled_write_cmd_data(0xaf, OLED_CMD); /* set dispkay on */else        oled_write_cmd_data(0xae, OLED_CMD); /* set dispkay off */}

OLED清屏：

staticvoidoled_disp_clear(void){uint8_t x, y;for (y = 0; y < 8; y++)    {        oled_set_pos(0, y);for (x = 0; x < 128; x++)            oled_write_cmd_data(0, OLED_DATA); /* 清零 */    }}

OLED初始化：

staticvoidoled_disp_test(void){uint8_t x, y;for (y = 0; y < 8; y++)    {        oled_set_pos(0, y);for (x = 0; x < 128; x++)        {if (x % 2 == 0)                oled_write_cmd_data(0, OLED_DATA);else                oled_write_cmd_data(1, OLED_DATA);        }    }}staticintoled_init(void){int ret = 0;    oled_reset();    ret = oled_write_cmd_data(0xae, OLED_CMD); //关闭显示    ret = oled_write_cmd_data(0x00, OLED_CMD); //设置 lower column address    ret = oled_write_cmd_data(0x10, OLED_CMD); //设置 higher column address    ret = oled_write_cmd_data(0x40, OLED_CMD); //设置 display start line    ret = oled_write_cmd_data(0xB0, OLED_CMD); //设置page address    ret = oled_write_cmd_data(0x81, OLED_CMD); // contract control    ret = oled_write_cmd_data(0x66, OLED_CMD); // 128    ret = oled_write_cmd_data(0xa1, OLED_CMD); //设置 segment remap    ret = oled_write_cmd_data(0xa6, OLED_CMD); // normal /reverse    ret = oled_write_cmd_data(0xa8, OLED_CMD); // multiple ratio    ret = oled_write_cmd_data(0x3f, OLED_CMD); // duty = 1/64    ret = oled_write_cmd_data(0xc8, OLED_CMD); // com scan direction    ret = oled_write_cmd_data(0xd3, OLED_CMD); // set displat offset    ret = oled_write_cmd_data(0x00, OLED_CMD); //    ret = oled_write_cmd_data(0xd5, OLED_CMD); // set osc division    ret = oled_write_cmd_data(0x80, OLED_CMD); //    ret = oled_write_cmd_data(0xd9, OLED_CMD); // ser pre-charge period    ret = oled_write_cmd_data(0x1f, OLED_CMD); //    ret = oled_write_cmd_data(0xda, OLED_CMD); // set com pins    ret = oled_write_cmd_data(0x12, OLED_CMD); //    ret = oled_write_cmd_data(0xdb, OLED_CMD); // set vcomh    ret = oled_write_cmd_data(0x30, OLED_CMD); //    ret = oled_write_cmd_data(0x8d, OLED_CMD); // set charge pump disable    ret = oled_write_cmd_data(0x14, OLED_CMD); //    ret = oled_write_cmd_data(0xaf, OLED_CMD); // set dispkay on    oled_disp_clear();    oled_set_pos(0, 0);return ret;}

• oled_reset，初始化必须调用复位，不然显示不了
• oled_disp_clear，初始化还需要清屏，不然可能初始化完屏幕会显示乱码。

2、OLED Linux SPI驱动框架

数据结构、命令定义：oled_def.h

#ifndef _OLED_DEF_H_#define _OLED_DEF_H_typedefunsignedcharuint8_t;typedefunsignedshortuint16_t;typedefunsignedintuint32_t;#define OLED_CMD_SET_XY                   0x01       /* 显示开关*/#define OLED_CMD_WRITE_DATAS              0x02#define OLED_CMD_SET_XY_WRITE_DATAS       0x03#define OLED_CMD_DISP_ON_OFF              0x04#define CMD_COMBINE(cmd, datasize)        (cmd | (datasize << 8))         /* 命令和数据大小组合 */structoled_disp_buffer {uint8_t x;uint8_t y;uint16_t len;uint8_t *buffer;};typedefstructoled_disp_bufferoled_disp_buf_t;#endif/* _OLED_DEF_H_ */

核心的file_operations：

//static ssize_t _drv_read(struct file *filp, char __user *buf, size_t size, loff_t *offset)//{//    int ret = 0;//    oled_disp_test();//    printk("%s %s\r\n", __FUNCTION__, DEV_NAME);//    ret = size;//    return ret;//}staticlong _drv_ioctl(struct file *filp, unsignedint cmd, unsignedlong arg){int ret = 0;uint8_t buf[3];uint16_t size;constvoid __user *userspace = (constvoid __user *)arg;switch (cmd & 0x0f)                /* 最低字节存放命令字段 */    {case OLED_CMD_DISP_ON_OFF:        ret = copy_from_user(&buf[0], userspace, 1);        oled_disp_on_off(buf[0]);break;case OLED_CMD_SET_XY:        ret = copy_from_user(&buf, userspace, 2);if (ret > 0) {            ret = -EFAULT;gotoexit;        }// printk("x %d, y %d\r", buf[0], buf[1]);        oled_set_pos(buf[0], buf[1]);break;case OLED_CMD_WRITE_DATAS:        size = (uint16_t)(cmd & 0xffffff00);        /* 前三字节存放数据大小 */        size >>= 8;// printk("size %d\r", size);        ret = copy_from_user(oled_dev->databuf, userspace, size);if (ret > 0) {            ret = -EFAULT;gotoexit;        }        oled_write_datas(oled_dev->databuf, size);case OLED_CMD_SET_XY_WRITE_DATAS:        ret = copy_from_user(buf, userspace, size);if (ret > 0) {            ret = -EFAULT;gotoexit;        }break;    }exit:return ret;}staticint _drv_release(struct inode *node, struct file *filp){structoled_device *tmp_oled = filp->private_data;    oled_disp_on_off(0);    oled_reset();return0;}staticstructfile_operationsoled_drv_ops = {    .owner = THIS_MODULE,    .open = _drv_open,//    .read = _drv_read,    .unlocked_ioctl = _drv_ioctl,    .release = _drv_release,};

probe和remove实现：

staticint _driver_probe(struct spi_device *spi){int err = 0;structdevice *_dev;structdevice_node *_dts_node;// struct device_node *oled_dev_node;    oled_dev = (struct oled_device *)kzalloc(sizeof(struct oled_device), GFP_KERNEL);if (!oled_dev)    {        printk("can't kzalloc mpu6050 dev\n");return -ENOMEM;    }    _dts_node = spi->dev.of_node;if (!_dts_node)    {        printk("oled espi can not found!\r\n");        err = -EINVAL;goto exit_free_dev;    }    oled_dev->dc_gpio = of_get_named_gpio(_dts_node, DC_GPIO_DTS_NAME, 0); /* 获取dc_gpio */if (!gpio_is_valid(oled_dev->dc_gpio))    {        printk("don't get oled %s!!!\n", DC_GPIO_DTS_NAME);        err = -EINVAL;goto exit_free_dev;    }    printk("oled dc-gpio %d", oled_dev->dc_gpio);    gpio_direction_output(oled_dev->dc_gpio, 1); /* 设置gpio为输入 */    oled_dev->rst_gpio = of_get_named_gpio(_dts_node, RST_GPIO_DTS_NAME, 0); /* 获取rst_gpio */if (!gpio_is_valid(oled_dev->rst_gpio))    {        printk("don't get oled %s!!!\n", RST_GPIO_DTS_NAME);        err = -EINVAL;goto exit_free_dev;    }    printk("oled dc-gpio %d", oled_dev->rst_gpio);    gpio_direction_output(oled_dev->rst_gpio, 1); /* 设置gpio为输入 *//* 内核自动分配设备号 */    err = alloc_chrdev_region(&oled_dev->dev_no, 0, 1, DEV_NAME);if (err < 0)    {        pr_err("Error: failed to register oled, err: %d\n", err);goto exit_free_dev;    }    cdev_init(&oled_dev->chrdev, &oled_drv_ops);    err = cdev_add(&oled_dev->chrdev, oled_dev->dev_no, 1);if (err)    {        printk("cdev add failed\r\n");goto exit_unregister;    }    oled_dev->class = class_create(THIS_MODULE, DEV_NAME);if (IS_ERR(oled_dev->class))    {        err = PTR_ERR(oled_dev->class);goto exit_cdev_del;    }/* 创建设备节点 */    _dev = device_create(oled_dev->class, NULL, oled_dev->dev_no, NULL, DEV_NAME);if (IS_ERR(_dev))    { /* 判断指针是否合法 */        err = PTR_ERR(_dev);goto exit_class_del;    }    oled_dev->spi = spi;    mutex_init(&oled_dev->m_lock); /* 初始化互斥锁  */    printk("%s probe success\r\n", DEV_NAME);gotoexit;exit_class_del:    class_destroy(oled_dev->class);exit_cdev_del:    cdev_del(&oled_dev->chrdev);exit_unregister:    unregister_chrdev_region(oled_dev->dev_no, 1); /* 注销设备 */exit_free_dev:    kfree(oled_dev);    oled_dev = NULL;exit:return err;}staticint _driver_remove(struct spi_device *spi){int ret = 0;    device_destroy(oled_dev->class, oled_dev->dev_no);    class_destroy(oled_dev->class);    cdev_del(&oled_dev->chrdev);    unregister_chrdev_region(oled_dev->dev_no, 1); /* 注销设备 */    kfree(oled_dev);    printk(KERN_INFO "%s remove success\n", DEV_NAME);return ret;}

出口入口函数实现：

/* 设备树的匹配列表 */staticstructof_device_iddts_match_table[] = {    {.compatible = OLED_DTS_COMPATIBLE}, /* 通过设备树来匹配 */    {},};/* 传统匹配方式 ID 列表 */staticconststructspi_device_idspi_dev_id[] = {    {.name = OLED_DTS_COMPATIBLE, 0},    {}};/* SPI 驱动结构体 */staticstructspi_driveroled_driver = {    .probe = _driver_probe,    .remove = _driver_remove,    .driver = {        .owner = THIS_MODULE,        .name = OLED_DTS_COMPATIBLE,        .of_match_table = dts_match_table,    },    .id_table = spi_dev_id,};module_spi_driver(oled_driver);MODULE_AUTHOR("Ares");MODULE_LICENSE("GPL");

3、驱动编译

oled\Makefile ：

KERN_DIR = /home/ares/work/ebf_linux_kernel-ebf_4.19.35_imx6ulall:    make -C $(KERN_DIR) M=`pwd` modules     $(CROSS_COMPILE)gcc -o oled_test oled_test.cclean:    make -C $(KERN_DIR) M=`pwd` clean    rm -rf modules.order  oled_test# 参考内核源码drivers/char/ipmi/Makefile# 要想把a.c, b.c编译成ab.ko, 可以这样指定:# ab-y := a.o b.o# obj-m += ab.oobj-m += oled_drv.o

执行make

测试程序

#include"stdio.h"#include<sys/types.h>#include<sys/stat.h>#include<fcntl.h>#include<unistd.h>#include<stdio.h>#include<string.h>#include<sys/ioctl.h>#include<poll.h>#include<stdint.h>#include<stdlib.h>#include"oled_def.h"#include"font.h"#define DEV_NAME   "/dev/oled"int oled_fd;voidsleep_ms(unsignedint ms){structtimevaldelay;    delay.tv_sec = 0;    delay.tv_usec = ms * 1000;     select(0, NULL, NULL, NULL, &delay);}voidoled_disp_char(int x, int y, unsignedchar c){int i = 0;/* 得到字模 */constunsignedchar *dots = oled_asc2_8x16[c - ' '];char pos[2];#if 0/* 发给OLED */    OLED_DIsp_Set_Pos(x, y);/* 发出8字节数据 */for (i = 0; i < 8; i++)        oled_write_cmd_data(dots[i], OLED_DATA);#endif    pos[0] = x;    pos[1] = y;    ioctl(oled_fd, CMD_COMBINE(OLED_CMD_SET_XY, 2), &pos);    ioctl(oled_fd, CMD_COMBINE(OLED_CMD_WRITE_DATAS, 8), dots);#if 0    OLED_DIsp_Set_Pos(x, y+1);/* 发出8字节数据 */for (i = 0; i < 8; i++)        oled_write_cmd_data(dots[i+8], OLED_DATA);#endif    pos[0] = x;    pos[1] = y+1;    ioctl(oled_fd, CMD_COMBINE(OLED_CMD_SET_XY, 2), pos);    ioctl(oled_fd, CMD_COMBINE(OLED_CMD_WRITE_DATAS, 8), &dots[8]);}voidoled_disp_string(uint8_t x, uint8_t y, char *str){uint8_t j = 0;while (str[j])    {                oled_disp_char(x, y, str[j]);  /* 显示单个字符 */        x += 8;if(x > 127)        {            x = 0;            y += 2;        }          j++;    /* 移动显示位置 */    }}staticvoidoled_test(void){    oled_disp_string(0, 0, "Sad!");    oled_disp_string(0, 2, "Bad!");    oled_disp_string(0, 4, "Moonlight");}intmain(int argc, char **argv){int ret;/* 2. 打开文件 */    oled_fd = open(DEV_NAME, O_RDWR | O_NONBLOCK);   // | O_NONBLOCKif (oled_fd < 0)    {printf("can not open file %s, %d\n", DEV_NAME, oled_fd);return-1;    }    oled_test();    sleep_ms(5000);    close(oled_fd);return0;}

测试：

sudo insmod oled_drv.ko      /* 安装驱动 */sudo ./oled_test             /* 执行app程序 */sudo rmmod oled_drv.ko       /* 卸载驱动 */