12.2内核空间基于SPI总线的OLED驱动

在内核空间编写SPI设备驱动的要点

  1. 在SPI总线控制器的设备树节点下增加SPI设备的设备树节点,节点中必须包含 reg 属性、 compatible 属性、 spi-max-frequency 属性, reg 属性用于描述片选索引, compatible属性用于设备和驱动的匹配, spi-max-frequency 用于描述设备可支持的最大 SPI 总线频率,在注册SPI总线控制器会解析其中的子节点,并注册成SPI设备。
  2. 创建并初始化struct spi_driver对象,其中重点关注of_match_table、probe、remove,of_match_table用于设备树和驱动匹配,probe在设备驱动匹配成功时执行,remove在设备或驱动卸载时执行。
  3. 在模块初始化函数中使用int spi_register_driver(struct spi_driver *sdrv)注册SPI设备驱动
  4. 使用void spi_message_init(struct spi_message *m)和void spi_message_add_tail(struct spi_transfer *t, struct spi_message *m)组织数据包,然后使用int spi_sync(struct spi_device *spi, struct spi_message *message)或int spi_async(struct spi_device *spi, struct spi_message *message)传输数据包
  5. 在模块卸载函数中使用void spi_unregister_driver(struct spi_driver *sdrv)注销SPI设备驱动

SPI OLED驱动编写

OLED模块原理图

模块一共由7个引脚,采用SPI模式时引脚定义如下:
GND:电源地
VCC:2.2V~5.5V
SCL(D0):CLK 时钟 (高电平 2.2V~5.5V)
SDA(D1):MOSI 数据(高电平 2.2V~5.5V)
RST:复位(高电平 2.2V~5.5V)
D/C:数据/命令(高电平 2.2V~5.5V)
CS:SPI片选
注意:没有MISO引脚,因为主控只能向OLED写数据,不能读取OLED的数据
12.2内核空间基于SPI总线的OLED驱动_第1张图片

与主控的连接示意图

12.2内核空间基于SPI总线的OLED驱动_第2张图片
要操作OLED,只需使用SPI接口发送数据,并不需要使用SPI接口读取数据。除此之外,还需要控制D/C引脚:

  • 当DC引脚是低电平时,是命令:比如复位、打开显示、设置地址
  • 当DC引脚是高电平时,是数据:写入要显示的数据

显存和像素

OLED上有128*64个像素(128列,64行),每个像素只有2种状态:亮、灭。
12.2内核空间基于SPI总线的OLED驱动_第3张图片
OLED内部有一块显存GDDRAM(Graphic Display Data RAM),显存中每位对应一个像素,入下图所示
12.2内核空间基于SPI总线的OLED驱动_第4张图片

  • byte0对应屏幕左上角竖向排列的8个像素,即COL0第0~第7行的8个像素
  • byte1对应COL1列第0~第7行的8个像素
  • ……
  • byte127对应COL127列第0~第7行的8个像素
  • byte128对应COL0那列第8~第15行的8个像素
  • ……

显存寻址模式

显存被分为8页、128列,要写某个字节时,需要先指定地址(哪页、哪列),然后写入1字节的数据。
OLED有三种寻址模式:

  • 页地址模式(Page addressing mode):每写入1个字节,行地址不变,列地址增1,列地址达到127后会从0开始
    12.2内核空间基于SPI总线的OLED驱动_第5张图片
  • 水平地址模式(Horizontal addressing mode):每写入1个字节,行地址不变,列地址增1,列地址达到127后从0开始,行地址指向下一页,列地址达到127、行地址达到7时,列地址和行地址都被复位为0,指向左上角(在此驱动中初始化时将地址设置为此模式)
    12.2内核空间基于SPI总线的OLED驱动_第6张图片
  • 垂直地址模式(Vertical addressing mode): 每写入1个字节,行地址增1,列地址不变,行地址达到7后从0开始,列地址指向下一列, 列地址达到127、行地址达到7时,列地址和行地址都被复位为0,指向左上角
    12.2内核空间基于SPI总线的OLED驱动_第7张图片

编写OLED设备树

  1. 在 stm32mp15-pinctrl.dtsi 的 &pinctrl_z 节点中修改 SPI 的引脚配置为如下内容:
	spi1_pins_a: spi1-0 {
		pins1 {
			pinmux = <STM32_PINMUX('Z', 0, AF5)>, /* SPI1_SCK */
				 <STM32_PINMUX('Z', 2, AF5)>; /* SPI1_MOSI */
			bias-disable;
			drive-push-pull;
			slew-rate = <3>;
		};

		pins2 {
			pinmux = <STM32_PINMUX('Z', 1, AF5)>; /* SPI1_MISO */
			bias-disable;
			drive-push-pull;
			slew-rate = <3>;
		};
	};

	spi1_sleep_pins_a: spi1-sleep-0 {
		pins {
			pinmux = <STM32_PINMUX('Z', 0, ANALOG)>, /* SPI1_SCK */
				 <STM32_PINMUX('Z', 1, ANALOG)>, /* SPI1_MISO */
				 <STM32_PINMUX('Z', 2, ANALOG)>; /* SPI1_MOSI */
		};
	};
  1. 在顶层设备树中引用spi1节点,并加入如下内容:
&spi1 {
	pinctrl-names = "default", "sleep";
	pinctrl-0 = <&spi1_pins_a>;
	pinctrl-1 = <&spi1_sleep_pins_a>;
	cs-gpios = <&gpioz 3 GPIO_ACTIVE_LOW>, <&gpioa 14 GPIO_ACTIVE_LOW>;
	status = "okay";

	/* OLED屏幕 */
	oled@1 {
		compatible = "atk,oled";
		reg = <1>; /* CS #1 */
		spi-max-frequency = <1000000>;
		dc-gpios = <&gpioi 3 GPIO_ACTIVE_LOW>;
		rst-gpios = <&gpioi 11 GPIO_ACTIVE_LOW>;
	};
};
  1. 用make ARCH=arm CROSS_COMPILE=arm-none-linux-gnueabihf- dtbs -j8编译设备树,并用新的.dtb文件启动系统

使能SPI控制器驱动

内核中使能 SPI 控制器驱动, ST 默认将SPI控制器驱动编译为模块,使能步骤如下:

  1. 执行命令make ARCH=arm CROSS_COMPILE=arm-none-linux-gnueabihf- menuconfig打开内核配置菜单
  2. 进行如下配置
Device Drivers
	SPI support (SPI [=y])
		<*> STMicroelectronics STM32 SPI controller //编译进内核
  1. 使用命令make ARCH=arm CROSS_COMPILE=arm-none-linux-gnueabihf- all LOADADDR=0XC2000040 -j16编译内核
  2. 使用命令make ARCH=arm CROSS_COMPILE=arm-none-linux-gnueabihf- uImage dtbs LOADADDR=0XC2000040 -j16生成uImage

驱动代码编写

OLED驱动程序基于SPI总线驱动框架和缓冲帧驱动框架编写,有关缓冲帧的内容参考8.1缓冲帧(Framebuffer)驱动框架和8.2LCD-TFT显示控制器驱动 (LCD驱动)部分,驱动代码主要包括以下几个部分:

  1. 注册/注销SPI设备驱动
  2. 注册/注销缓冲帧驱动
  3. OLED初始化
  4. OLED显示更新
    驱动代码的完成内容如下所示:
#include 
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#define OLED_DISPLAY_RAM_SIZE	(8*128)

struct oled_handle{
	struct spi_device *spi;				//oled所属spi设备
	int rst_gpio;						//复位引脚
	int dc_gpio;						//数据命令选择引脚
	struct task_struct *kthread;		//用于将显存内容更新到OLED的内核线程
	uint8_t (*oled_buffer)[128];		//oled buffer,将缓冲帧中的数据转换为OLED格式后在通过SPI总线发送到OLED
	struct fb_info *fb;					//缓冲帧句柄
	unsigned int pseudo_palette[16];	//调色板
	uint8_t (*fb_buffer)[16];			//缓冲帧
	dma_addr_t phy_addr;				//缓冲帧物理地址
	uint8_t (*old_fb_buffer)[16];		//缓冲帧上一次更新时的状态
};

//初始化OLED的复位引脚和数据命令选择引脚
static int devm_pin_init(struct oled_handle *oled)
{
	int result;

	//获取RST GPIO号
	oled->rst_gpio = of_get_named_gpio(oled->spi->dev.of_node, "rst-gpios", 0);
	if(oled->rst_gpio < 0)
	{
		printk("get rst_gpio failed\r\n");
		return oled->rst_gpio;
	}
	//申请RST GPIO
	result = devm_gpio_request(&oled->spi->dev, oled->rst_gpio, "oled,rst_gpio");
	if(result < 0)
	{
		printk("request rst_gpio failed\r\n");
		return result;
	}
	//设置复位引脚输出高电平
	gpio_direction_output(oled->rst_gpio, 1);

	//获取DC GPIO号
	oled->dc_gpio = of_get_named_gpio(oled->spi->dev.of_node, "dc-gpios", 0);
	if(oled->dc_gpio < 0)
	{
		printk("get dc_gpio failed\r\n");
		return oled->dc_gpio;
	}
	//申请DC GPIO
	result = devm_gpio_request(&oled->spi->dev, oled->dc_gpio, "oled,dc_gpio");
	if(result < 0)
	{
		printk("request dc_gpio failed\r\n");
		return result;
	}
	//设置数据/命令选择引脚输出高电平
	gpio_direction_output(oled->dc_gpio, 1);

	return 0;
}

//数据命令选择引脚拉高,表示发送数据
static void dc_high(struct oled_handle *oled)
{
	gpio_direction_output(oled->dc_gpio, 1);
}

//数据命令选择引脚拉低,表示发送命令
static void dc_low(struct oled_handle *oled)
{
	gpio_direction_output(oled->dc_gpio, 0);
}

//复位引脚拉高
static void rst_high(struct oled_handle *oled)
{
	gpio_direction_output(oled->rst_gpio, 1);
}

//复位引脚拉低
static void rst_low(struct oled_handle *oled)
{
	gpio_direction_output(oled->rst_gpio, 0);
}

//复位OLED屏幕
static void oled_reset(struct oled_handle *oled)
{
	//暂时拉高复位引脚
	rst_high(oled);
	msleep_interruptible(200);

	//拉低复位引脚,进行复位
	rst_low(oled);
	msleep_interruptible(200);
	//拉高复位引脚,复位结束
	rst_high(oled);
	msleep_interruptible(200);
}

//通过SPI总线向OLED设备发送数据
static int oled_write(struct oled_handle *oled, const uint8_t *data, uint32_t lenght)
{
	int result;
	uint8_t *buffer;
	struct spi_message message;
	struct spi_transfer transfer;

	//分配发送缓存
	buffer = kzalloc(lenght, GFP_KERNEL);
	if(!buffer)
		return -ENOMEM;
	//将数据拷贝到buffer中
	memcpy(buffer, data, lenght);

	//初始化spi_message
	spi_message_init(&message);

	//复位spi_transfer
	memset(&transfer, 0, sizeof(transfer));
	//发送缓存
	transfer.tx_buf = buffer;
	//接收缓存
	transfer.rx_buf = NULL;
	//传输的长度
	transfer.len = lenght;

	//将spi_transfer添加到spi_message队列
	spi_message_add_tail(&transfer, &message);

	//同步传输
	result = spi_sync(oled->spi, &message);

	//释放发送缓存
	kfree(buffer);

	return result;
}

//向OLED屏幕发送命令
static int oled_write_cmd(struct oled_handle *oled, uint8_t *command, uint32_t lenght)
{
	//拉低数据命令选择引脚,表示发送命令
	dc_low(oled);
	//通过SPI发送数据
	return oled_write(oled, command, lenght);
}

//向OLED屏幕发送数据
static int oled_write_data(struct oled_handle *oled, uint8_t *data, uint32_t lenght)
{
	//拉高数据命令选择引脚,表示发送数据
	dc_high(oled);
	//通过SPI发送数据
	return oled_write(oled, data, lenght);
}

//将oled_buffer中的数据显示在OLED屏幕上
static int oled_update(struct oled_handle *oled)
{
	int result;
	uint8_t command[3];

	//设置地址
	command[0] = 0xB0 + 0;					//设置页地址
	command[1] = 0x10 + 0;					//设置显示位置—列高地址高4位
	command[2] = 0x00 + 0;					//设置显示位置—列低地址低4位
	result = oled_write_cmd(oled, command, 3);
	if(result != 0)
		return result;

	//发送显示数据
	result = oled_write_data(oled, oled->oled_buffer[0], 128*8);
	if(result != 0)
		return result;

	return 0;
}

//初始化OLED屏幕
static int oled_init(struct oled_handle *oled)
{
	int result;
	uint8_t command[28];

	//复位OLED
	oled_reset(oled);
 
	//发送初始化命令
	command[0 ] = 0xAE;				//--turn off oled panel
	command[1 ] = 0x00;				//---set low column address
	command[2 ] = 0x10;				//---set high column address
	command[3 ] = 0x40;				//--set start line address  Set Mapping RAM Display Start Line (0x00~0x3F)
	command[4 ] = 0x81;				//--set contrast control register
	command[5 ] = 0xCF;				 // Set SEG Output Current Brightness
	command[6 ] = 0xA1;				//--Set SEG/Column Mapping     0xa0左右反置 0xa1正常
	command[7 ] = 0xC8;				//Set COM/Row Scan Direction   0xc0上下反置 0xc8正常
	command[8 ] = 0xA6;				//--set normal display
	command[9 ] = 0xA8;				//--set multiplex ratio(1 to 64)
	command[10] = 0x3F;				//--1/64 duty
	command[11] = 0xD3;				//-set display offset	Shift Mapping RAM Counter (0x00~0x3F)
	command[12] = 0x00;				//-not offset
	command[13] = 0xD5;				//--set display clock divide ratio/oscillator frequency
	command[14] = 0x80;				//--set divide ratio, Set Clock as 100 Frames/Sec
	command[15] = 0xD9;				//--set pre-charge period
	command[16] = 0xF1;				//Set Pre-Charge as 15 Clocks & Discharge as 1 Clock
	command[17] = 0xDA;				//--set com pins hardware configuration
	command[18] = 0x12;				
	command[19] = 0xDB;				//--set vcomh
	command[20] = 0x40;				//Set VCOM Deselect Level
	command[21] = 0x20;				//-Set Addressing Mode (0x00/0x01/0x02)
	command[22] = 0x00;				//
	command[23] = 0x8D;				//--set Charge Pump enable/disable
	command[24] = 0x14;				//--set(0x10) disable
	command[25] = 0xA4;				// Disable Entire Display On (0xa4/0xa5)
	command[26] = 0xA6;				// Disable Inverse Display On (0xa6/a7) 
	command[27] = 0xAF;				//--turn on oled panel 
	result = oled_write_cmd(oled, command, 28);
	if(result != 0)
		return result;

	//更新OLED显示
	return oled_update(oled);
}

//将缓冲帧中的像素转换成OLED格式
static void convert_fb_to_oled(struct oled_handle *oled)
{
	int i, j, k;

	//一共8*8行,其中每8行1byte
	for(i=0; i<8; i++) {
		//一个128列
		for(j=0; j<16; j++) {
			for(k=0; k<8; k++) {
				oled->oled_buffer[i][j*8+k] = (((oled->fb_buffer[i*8+0][j] >> k) & 0x01) << 0) |
					(((oled->fb_buffer[i*8+1][j] >> k) & 0x01) << 1) |
					(((oled->fb_buffer[i*8+2][j] >> k) & 0x01) << 2) |
					(((oled->fb_buffer[i*8+3][j] >> k) & 0x01) << 3) |
					(((oled->fb_buffer[i*8+4][j] >> k) & 0x01) << 4) |
					(((oled->fb_buffer[i*8+5][j] >> k) & 0x01) << 5) |
					(((oled->fb_buffer[i*8+6][j] >> k) & 0x01) << 6) |
					(((oled->fb_buffer[i*8+7][j] >> k) & 0x01) << 7);
			}
		}
	}
}

//内核线程,用于周期性刷新OLED显示屏
static int oled_thread(void *arg)
{
	struct oled_handle *oled;

	oled = (struct oled_handle*)arg;
	while(!kthread_should_stop())
	{
		//缓冲帧内容改变才刷新OLED
		if(memcmp(oled->old_fb_buffer, oled->fb_buffer, OLED_DISPLAY_RAM_SIZE))
		{
			//应用层可能正在进行写操作,这里延时休眠600~700us等待应用层写完
			usleep_range(600, 700);

			//显存格式转换
			convert_fb_to_oled(oled);

			//记录缓冲帧状态
			memcpy(oled->old_fb_buffer, oled->fb_buffer, OLED_DISPLAY_RAM_SIZE);

			//更新显示
			oled_update(oled);
		}
		else
		{
			//休眠
			msleep_interruptible(2);
		}
	}

	return 0;
}

static inline unsigned int chan_to_field(unsigned int chan, struct fb_bitfield *bf)
{
	chan &= 0xffff;
	chan >>= 16 - bf->length;
	return chan << bf->offset;
}

static int oled_setcolreg(unsigned regno, unsigned red, 
						unsigned green, unsigned blue, 
						unsigned transp, struct fb_info *info)
{
	unsigned int val;
	unsigned int *pseudo_palette;

	if (regno >= 16)
		return -EINVAL;

	val  = chan_to_field(red, &info->var.red);
	val |= chan_to_field(green, &info->var.green);
	val |= chan_to_field(blue, &info->var.blue);
	pseudo_palette = info->pseudo_palette;
	pseudo_palette[regno] = val;

	return 0;
}

//缓冲帧操作函数集合
static struct fb_ops oled_ops = {
	.owner = THIS_MODULE,
	.fb_setcolreg = oled_setcolreg,
	.fb_fillrect = cfb_fillrect,
	.fb_copyarea = cfb_copyarea,
	.fb_imageblit = cfb_imageblit,
};

static int oled_probe(struct spi_device *spi)
{
	int result;
	struct oled_handle *oled;

	printk("%s\r\n", __FUNCTION__);

	//设置SPI设备的DMA寻址范围,不然dma_alloc会执行失败
	spi->dev.coherent_dma_mask = DMA_BIT_MASK(32);

	//分配OLED句柄
	oled = devm_kmalloc(&spi->dev, sizeof(struct oled_handle), GFP_KERNEL);
	if(!oled)
	{
		printk("alloc oled_buffer failed\r\n");
		return -ENOMEM;
	}
	memset(oled, 0x00, sizeof(struct oled_handle));

	//分配oled缓存,缓冲帧中的数据经过格式转换后拷贝到oled_buffer中,然后在显示到屏幕
	oled->oled_buffer = devm_kmalloc(&spi->dev, OLED_DISPLAY_RAM_SIZE, GFP_KERNEL);
	if(!oled->oled_buffer)
	{
		printk("alloc oled_buffer failed\r\n");
		return -ENOMEM;
	}
	memset(oled->oled_buffer, 0x00, OLED_DISPLAY_RAM_SIZE);

	//分配old_fb缓存,用于存储上一次更新显示器时缓冲帧中的状态
	oled->old_fb_buffer = devm_kmalloc(&spi->dev, OLED_DISPLAY_RAM_SIZE, GFP_KERNEL);
	if(!oled->old_fb_buffer)
	{
		printk("alloc old_fb_buffer failed\r\n");
		return -ENOMEM;
	}
	memset(oled->old_fb_buffer, 0x00, OLED_DISPLAY_RAM_SIZE);

	//分配缓冲帧
	oled->fb_buffer = dma_alloc_wc(&spi->dev, OLED_DISPLAY_RAM_SIZE, &oled->phy_addr, GFP_KERNEL);
	if(!oled->fb_buffer)
	{
		printk("alloc fb_buffer failed\r\n");
		return -ENOMEM;
	}
	memset(oled->fb_buffer, 0x00, OLED_DISPLAY_RAM_SIZE);

	//设置SPI设备的驱动私有数据
	spi->dev.driver_data = (void*)oled;

	//给oled句柄绑定SPI设备
	oled->spi = spi;

	//设置SPI模式,也可以在设备树中进行配置
	/*MODE3(CPOL=1,CPHA=1)*/
	oled->spi->mode = SPI_MODE_3;
	spi_setup(oled->spi);

	//初始化OLED的GPIO
	result = devm_pin_init(oled);
	if(result < 0)
	{
		dma_free_wc(&spi->dev, OLED_DISPLAY_RAM_SIZE, oled->fb_buffer, oled->phy_addr);
		printk("init gpio failed\r\n");
		return result;
	}

	//初始化OLED屏幕
	result = oled_init(oled);
	if(result < 0)
	{
		dma_free_wc(&spi->dev, OLED_DISPLAY_RAM_SIZE, oled->fb_buffer, oled->phy_addr);
		printk("oled_init failed\r\n");
		return result;
	}

	//分配缓冲帧句柄
	oled->fb = framebuffer_alloc(0, &spi->dev);
	if(!oled->fb)
	{
		dma_free_wc(&spi->dev, OLED_DISPLAY_RAM_SIZE, oled->fb_buffer, oled->phy_addr);
		printk("alloc fb failed\r\n");
		return -ENOMEM;
	}

	//设置fb
	//显存虚拟地址和大小
	oled->fb->screen_base = (char*)oled->fb_buffer;
	oled->fb->screen_size = OLED_DISPLAY_RAM_SIZE;
	//LCD分辨率、颜色格式
	oled->fb->var.xres = 128;
	oled->fb->var.yres = 64;
	oled->fb->var.xres_virtual = 128;
	oled->fb->var.yres_virtual = 64;
	oled->fb->var.bits_per_pixel = 1;
	//ID
	strcpy(oled->fb->fix.id, "atk,oled");
	//显存大小和物理地址
	oled->fb->fix.smem_len = OLED_DISPLAY_RAM_SIZE;
	oled->fb->fix.smem_start = oled->phy_addr;
	//一行的显存长度
	oled->fb->fix.line_length = 16;
	//显示器类型
	oled->fb->fix.type = FB_TYPE_PACKED_PIXELS;
	//像素格式
	oled->fb->fix.visual = FB_VISUAL_MONO10;
	//底层操作函数集合
	oled->fb->fbops = &oled_ops;
	//颜色表
	oled->fb->pseudo_palette = oled->pseudo_palette;

	//注册缓冲帧驱动
	result = register_framebuffer(oled->fb);
	if(result < 0)
	{
		framebuffer_release(oled->fb);
		dma_free_wc(&spi->dev, OLED_DISPLAY_RAM_SIZE, oled->fb_buffer, oled->phy_addr);
		printk("register fb failed\r\n");
		return result;
	}

	//创建内核线程,更新OLED
	oled->kthread = kthread_create(oled_thread, (void*)oled, "oled_thread%d,%d", oled->spi->controller->bus_num, oled->spi->chip_select);
	if(IS_ERR(oled->kthread))
	{
		unregister_framebuffer(oled->fb);
		framebuffer_release(oled->fb);
		dma_free_wc(&spi->dev, OLED_DISPLAY_RAM_SIZE, oled->fb_buffer, oled->phy_addr);
		printk("create oled_thread failed\r\n");
		return PTR_ERR(oled->kthread);
	}
	wake_up_process(oled->kthread);

	return 0;
}

//设备或驱动卸载时执行
static int oled_remove(struct spi_device *spi)
{
	struct oled_handle *oled;

	printk("%s\r\n", __FUNCTION__);

	oled = (struct oled_handle*)spi->dev.driver_data;
	if(!oled)
	{
		printk("verification failed\r\n");
		return -EINVAL;
	}

	//停止内核线程
	kthread_stop(oled->kthread);
	//注销缓冲帧驱动
	unregister_framebuffer(oled->fb);
	//释放缓冲帧句柄
	framebuffer_release(oled->fb);
	//释放缓冲帧
	dma_free_wc(&spi->dev, OLED_DISPLAY_RAM_SIZE, oled->fb_buffer, oled->phy_addr);

	return 0;
}

//匹配列表,用于设备树和平台驱动匹配
static const struct of_device_id oled_of_match[] = {
	{.compatible = "atk,oled"},
	{ /* Sentinel */}
};
//传统匹配方式ID列表
static const struct spi_device_id oled_id[] = {
	{}
};
//SPI驱动
static struct spi_driver oled_drv = {
	.driver = {
		.name = "oled",
		.owner = THIS_MODULE,
		.pm = NULL,
		.of_match_table = oled_of_match,
	},
	.id_table = oled_id,
	.probe = oled_probe,
	.remove = oled_remove,
};
static int __init oled_drv_init(void)
{
	int result = 0;

	printk("%s\r\n", __FUNCTION__);

	//注册SPI设备驱动
	result = spi_register_driver(&oled_drv);
	if(result < 0)
	{
		printk("add cdev failed\r\n");
		return result;
	}

	return 0;
}

static void __exit oled_drv_exit(void)
{
	printk("%s\r\n", __FUNCTION__);

	//注销SPI驱动
	spi_unregister_driver(&oled_drv);
}

module_init(oled_drv_init);
module_exit(oled_drv_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("CSDN");
MODULE_DESCRIPTION("oled_dev");

编写驱动测试程序

OLED应用程序开发步骤如下:

  1. 打开缓冲帧设备
  2. 获取屏幕参数,主要包括屏幕x、y像素个数,以及每个像素的bit数,然后计算出显存的大小
  3. 通过mmap函数映射显存地址到用户空间
  4. 通过向映射到用户空间的显存写入数据,以控制在OLED上的显示内容
  5. 使用完成后取消mmap的映射。关闭设备
    如下是OLED测试程序的主函数,其中oled_lib对OLED的常用功能进行了封装,比如初始化、反初始化、画线、画方块、读写像素点等,初始化完成的内容包括上面的1~3步,反初始化完成的上面的第5步,其他接口均是读写显存。
#include 
#include "oled_lib.h"

int main(int argc, char *argv[])
{
	if(argc < 2)
	{
		printf("Error Usage!\r\n");
		return -1;
	}

	oled_init(argv[1]);

	while(1)
	{
		oled_clear();
		usleep(100*1000);
		display_line(0, 0, 127, 63);
		usleep(100*1000);
		display_line(0, 63, 127, 31);
		usleep(100*1000);
		display_rect(55, 5, 50, 20);

		sleep(1);
	}

	return 0;
}

上机测试

  1. 修改设备树(设备树需要结合硬件进行修改),然后编译设备树,并用新的设备树启动
  2. 从这里下载代码,并进行编译,然后拷贝到目标板根文件系统的root目录
  3. 执行命令insmod oled.ko加载OLED驱动,加载完成后在/dev目录增加了一个以fb开通的缓冲帧设备文件
    12.2内核空间基于SPI总线的OLED驱动_第8张图片
  4. 执行命令./oled_app.out /dev/fb0运行测试命令(/dev/fb0是OLED的缓冲帧设备),可以看到屏幕上显示相应的测试图像,终端也会打印屏幕的参数。
    在这里插入图片描述

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