diff --git a/IMX6ULL/doc_pic/09_UART/15_编写虚拟UART驱动程序_实现数据传输.md b/IMX6ULL/doc_pic/09_UART/15_编写虚拟UART驱动程序_实现数据传输.md
new file mode 100644
index 0000000..d36bc34
--- /dev/null
+++ b/IMX6ULL/doc_pic/09_UART/15_编写虚拟UART驱动程序_实现数据传输.md
@@ -0,0 +1,136 @@
+## 编写虚拟UART驱动程序\_实现数据传输
+
+* 参考代码
+
+  ```shell
+  硬件相关：
+  drivers/tty/serial/imx.c
+  drivers/tty/serial/stm32-usart.c
+  
+  串口核心层：
+  drivers/tty/serial/serial_core.c
+  
+  TTY层:
+  drivers/tty/tty_io.c
+  ```
+
+  
+
+* 本节课程源码在GIT仓库里
+
+  ```shell
+  doc_and_source_for_drivers\IMX6ULL\source\09_UART
+  	06_virtual_uart_driver_txrx
+  doc_and_source_for_drivers\STM32MP157\source\A7\09_UART
+  	06_virtual_uart_driver_txrx
+  ```
+  
+  
+
+### 1. 虚拟UART的驱动组成
+
+![image-20210730142813809](pic/09_UART/39_uart_driver.png)
+
+
+
+### 2. 虚拟UART的数据流程
+
+![image-20210730150445225](pic/09_UART/40_virtual_uart.png)
+
+为了做实验，我们还要创建一个虚拟文件：/proc/virt_uart_buf
+
+* 要发数据给虚拟串口时，执行：echo "xxx" > /proc/virt_uart_buf
+* 要读取虚拟串口的数据时，执行：cat /proc/virt_uart_buf
+
+
+
+### 3. 实现/proc文件
+
+参考`/proc/cmdline`，怎么找到它对应的驱动？在Linux内核源码下执行以下命令搜索：
+
+```shell
+grep "cmdline" * -nr | grep proc
+```
+
+得到：
+
+```shell
+fs/proc/cmdline.c:26:   proc_create("cmdline", 0, NULL, &cmdline_proc_fops);
+```
+
+
+
+### 4. 触发中断
+
+使用如下函数：
+
+```c
+int irq_set_irqchip_state(unsigned int irq, enum irqchip_irq_state which,
+			  bool val);
+```
+
+怎么找到它的？在中断子系统中，我们知道往GIC寄存器GICD_ISPENDRn写入某一位就可以触发中断。内核代码中怎么访问这些寄存器？
+在`drivers\irqchip\irq-gic.c`中可以看到irq_chip中的"irq_set_irqchip_state"被用来设置中断状态：
+
+```c
+static struct irq_chip gic_chip = {
+	.irq_mask		= gic_mask_irq,
+	.irq_unmask		= gic_unmask_irq,
+	.irq_eoi		= gic_eoi_irq,
+	.irq_set_type		= gic_set_type,
+	.irq_get_irqchip_state	= gic_irq_get_irqchip_state,
+	.irq_set_irqchip_state	= gic_irq_set_irqchip_state, /* 2. 继续搜"irq_set_irqchip_state" */
+	.flags			= IRQCHIP_SET_TYPE_MASKED |
+				  IRQCHIP_SKIP_SET_WAKE |
+				  IRQCHIP_MASK_ON_SUSPEND,
+};
+
+static int gic_irq_set_irqchip_state(struct irq_data *d,
+				     enum irqchip_irq_state which, bool val)
+{
+	u32 reg;
+
+	switch (which) {
+	case IRQCHIP_STATE_PENDING:
+		reg = val ? GIC_DIST_PENDING_SET : GIC_DIST_PENDING_CLEAR; /* 1. 找到寄存器 */
+		break;
+
+	case IRQCHIP_STATE_ACTIVE:
+		reg = val ? GIC_DIST_ACTIVE_SET : GIC_DIST_ACTIVE_CLEAR;
+		break;
+
+	case IRQCHIP_STATE_MASKED:
+		reg = val ? GIC_DIST_ENABLE_CLEAR : GIC_DIST_ENABLE_SET;
+		break;
+
+	default:
+		return -EINVAL;
+	}
+
+	gic_poke_irq(d, reg);
+	return 0;
+}
+```
+
+
+
+继续搜"irq_set_irqchip_state"，在`drivers\irqchip\irq-gic.c`中可以看到：
+
+```c
+int irq_set_irqchip_state(unsigned int irq, enum irqchip_irq_state which,
+			  bool val)
+{
+    ......
+}
+
+EXPORT_SYMBOL_GPL(irq_set_irqchip_state);
+```
+
+
+
+以后就可与使用如下代码触发某个中断：
+
+```c
+irq_set_irqchip_state(irq, IRQCHIP_STATE_PENDING, 1);
+```
+
diff --git a/IMX6ULL/doc_pic/09_UART/15_编写虚拟UART驱动程序_实现数据传输.tif b/IMX6ULL/doc_pic/09_UART/15_编写虚拟UART驱动程序_实现数据传输.tif
new file mode 100644
index 0000000..7333f25
Binary files /dev/null and b/IMX6ULL/doc_pic/09_UART/15_编写虚拟UART驱动程序_实现数据传输.tif differ
diff --git a/IMX6ULL/doc_pic/09_UART/16_编写虚拟UART驱动程序_调试.md b/IMX6ULL/doc_pic/09_UART/16_编写虚拟UART驱动程序_调试.md
new file mode 100644
index 0000000..0a75d98
--- /dev/null
+++ b/IMX6ULL/doc_pic/09_UART/16_编写虚拟UART驱动程序_调试.md
@@ -0,0 +1,211 @@
+## 编写虚拟UART驱动程序_调试
+
+* 参考代码
+
+  ```shell
+  硬件相关：
+  drivers/tty/serial/imx.c
+  drivers/tty/serial/stm32-usart.c
+  
+  串口核心层：
+  drivers/tty/serial/serial_core.c
+  
+  TTY层:
+  drivers/tty/tty_io.c
+  ```
+
+  
+
+* 本节课程源码在GIT仓库里
+
+  ```shell
+  doc_and_source_for_drivers\IMX6ULL\source\09_UART
+  	07_virtual_uart_driver_ok
+  doc_and_source_for_drivers\STM32MP157\source\A7\09_UART
+  	07_virtual_uart_driver_ok
+  ```
+  
+
+
+
+### 1. 实验流程
+
+![image-20210806120309603](pic/09_UART/41_data_flow.png)
+
+
+
+### 2. 上机实验
+
+#### 2.1 设置工具链
+
+##### 1. STM32MP157
+
+  ```shell
+  export ARCH=arm
+  export CROSS_COMPILE=arm-buildroot-linux-gnueabihf-
+  export PATH=$PATH:/home/book/100ask_stm32mp157_pro-sdk/ToolChain/arm-buildroot-linux-gnueabihf_sdk-buildroot/bin
+  ```
+
+##### 2. IMX6ULL
+
+  ```shell
+  export ARCH=arm
+  export CROSS_COMPILE=arm-linux-gnueabihf-
+  export PATH=$PATH:/home/book/100ask_imx6ull-sdk/ToolChain/gcc-linaro-6.2.1-2016.11-x86_64_arm-linux-gnueabihf/bin
+  ```
+
+
+
+#### 2.2 编译、替换设备树
+
+##### 1. STM32MP157
+
+  * 修改`arch/arm/boot/dts/stm32mp157c-100ask-512d-lcd-v1.dts`，添加如下代码：
+
+    ```shell
+    / {
+    	virtual_uart: virtual_uart_100ask {
+    		compatible = "100ask,virtual_uart";
+    		
+    		interrupt-parent = <&intc>;
+    		interrupts = <GIC_SPI 99 IRQ_TYPE_LEVEL_HIGH>;
+    		
+    	};
+    };
+    ```
+
+    
+
+  * 编译设备树：
+    在Ubuntu的STM32MP157内核目录下执行如下命令,
+    得到设备树文件：`arch/arm/boot/dts/stm32mp157c-100ask-512d-lcd-v2.dtb`
+
+    ```shell
+    make dtbs
+    ```
+
+  * 复制到NFS目录：
+
+    ```shell
+    $ cp arch/arm/boot/dts/stm32mp157c-100ask-512d-lcd-v2.dtb ~/nfs_rootfs/
+    ```
+
+  * 开发板上挂载NFS文件系统
+
+    * vmware使用NAT(假设windowsIP为192.168.2.100)
+
+      ```shell
+      [root@100ask:~]# mount -t nfs -o nolock,vers=3,port=2049,mountport=9999 
+      192.168.2.100:/home/book/nfs_rootfs /mnt
+      ```
+
+    * vmware使用桥接，或者不使用vmware而是直接使用服务器：假设Ubuntu IP为192.168.2.137
+
+      ```shell
+      [root@100ask:~]#  mount -t nfs -o nolock,vers=3 192.168.2.137:/home/book/nfs_rootfs /mnt
+      ```
+
+* 更新设备树
+
+  ```shell
+  [root@100ask:~]# mount  /dev/mmcblk2p2  /boot
+  [root@100ask:~]# cp /mnt/stm32mp157c-100ask-512d-lcd-v1.dtb /boot
+  [root@100ask:~]# sync
+  ```
+
+* 重启开发板
+
+  
+
+
+
+##### 2. IMX6ULL
+
+  * 修改`arch/arm/boot/dts/100ask_imx6ull-14x14.dts`，添加如下代码：
+
+    ```shell
+    / {
+    	virtual_uart: virtual_uart_100ask {
+    		compatible = "100ask,virtual_uart";
+    		
+    		interrupt-parent = <&intc>;
+    		interrupts = <GIC_SPI 99 IRQ_TYPE_LEVEL_HIGH>;
+    		
+    	};
+    
+    };
+    ```
+
+    
+
+  * 编译设备树：
+    在Ubuntu的IMX6ULL内核目录下执行如下命令,
+    得到设备树文件：`arch/arm/boot/dts/100ask_imx6ull-14x14.dtb`
+
+    ```shell
+    make dtbs
+    ```
+
+  * 复制到NFS目录：
+
+    ```shell
+    $ cp arch/arm/boot/dts/100ask_imx6ull-14x14.dtb ~/nfs_rootfs/
+    ```
+
+* 开发板上挂载NFS文件系统
+
+  * vmware使用NAT(假设windowsIP为192.168.2.100)
+
+    ```shell
+    [root@100ask:~]# mount -t nfs -o nolock,vers=3,port=2049,mountport=9999 
+    192.168.2.100:/home/book/nfs_rootfs /mnt
+    ```
+
+  * vmware使用桥接，或者不使用vmware而是直接使用服务器：假设Ubuntu IP为192.168.2.137
+
+    ```shell
+    [root@100ask:~]#  mount -t nfs -o nolock,vers=3 192.168.2.137:/home/book/nfs_rootfs /mnt
+    ```
+
+  * 更新设备树
+
+    ```shell
+    [root@100ask:~]# cp /mnt/100ask_imx6ull-14x14.dtb /boot
+    [root@100ask:~]# sync
+    ```
+
+* 重启开发板
+
+
+
+#### 2.3 编译、安装驱动程序
+
+* 编译：
+
+  * 在Ubuntu上
+  * 修改`07_virtual_uart_driver_ok`中的Makefile，指定内核路径`KERN_DIR`，在执行`make`命令即可。
+
+* 安装：
+
+  * 在开发板上
+
+  * 挂载NFS，复制文件，insmod，类似如下命令：
+
+    ```shell
+    mount -t nfs -o nolock,vers=3 192.168.2.137:/home/book/nfs_rootfs /mnt
+    // 对于IMX6ULL，想看到驱动打印信息，需要先执行
+    echo "7 4 1 7" > /proc/sys/kernel/printk
+    
+    insmod -f /mnt/virtual_uart.ko
+    
+    ```
+
+* 观察内核打印的信息
+
+
+
+### 3. 调试
+
+根据框架、数据流程来调试：
+
+![](pic/09_UART/24_tty_driver_level_2.png)
\ No newline at end of file
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diff --git a/IMX6ULL/source/09_UART/06_virtual_uart_driver_txrx/virtual_uart.c b/IMX6ULL/source/09_UART/06_virtual_uart_driver_txrx/virtual_uart.c
new file mode 100644
index 0000000..e52a0bf
--- /dev/null
+++ b/IMX6ULL/source/09_UART/06_virtual_uart_driver_txrx/virtual_uart.c
@@ -0,0 +1,288 @@
+#include <linux/module.h>
+#include <linux/ioport.h>
+#include <linux/init.h>
+#include <linux/console.h>
+#include <linux/sysrq.h>
+#include <linux/platform_device.h>
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
+#include <linux/serial_core.h>
+#include <linux/serial.h>
+#include <linux/clk.h>
+#include <linux/delay.h>
+#include <linux/rational.h>
+#include <linux/reset.h>
+#include <linux/slab.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/io.h>
+#include <linux/dma-mapping.h>
+
+#include <asm/irq.h>
+
+#define BUF_LEN  1024
+#define NEXT_PLACE(i) ((i+1)&0x3FF)
+
+static struct uart_port	*virt_port;
+static unsigned char txbuf[BUF_LEN];
+static int tx_buf_r = 0;
+static int tx_buf_w = 0;
+
+static unsigned char rxbuf[BUF_LEN];
+static int rx_buf_r = 0;
+static int rx_buf_w = 0;
+
+static struct proc_dir_entry *uart_proc_file;
+
+
+static struct uart_driver virt_uart_drv = {
+	.owner          = THIS_MODULE,
+	.driver_name    = "VIRT_UART",
+	.dev_name       = "ttyVIRT",
+	.major          = 0,
+	.minor          = 0,
+	.nr             = 1,
+};
+
+
+/* circle buffer */
+
+
+static int is_txbuf_empty(void)
+{
+	return tx_buf_r == tx_buf_w;
+}
+
+static int is_txbuf_full(void)
+{
+	return NEXT_PLACE(tx_buf_w) == tx_buf_r;
+}
+
+static int txbuf_put(unsigned char val)
+{
+	if (is_txbuf_full())
+		return -1;
+	txbuf[tx_buf_w] = val;
+	tx_buf_w = NEXT_PLACE(tx_buf_w);
+	return 0;
+}
+
+static int txbuf_get(unsigned char *pval)
+{
+	if (is_txbuf_empty())
+		return -1;
+	*pval = g_events[tx_buf_r];
+	tx_buf_r = NEXT_PLACE(tx_buf_r);
+	return 0;
+}
+
+static int txbuf_count(void)
+{
+	if (tx_buf_w >= tx_buf_r)
+		return tx_buf_w - tx_buf_r;
+	else
+		return BUF_LEN + tx_buf_w - tx_buf_r;
+}
+
+
+
+ssize_t virt_uart_buf_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
+{
+	/* 把txbuf中的数据copy_to_user */
+	int cnt = txbuf_count();
+	int i;
+	unsigned char val;
+
+	cnt = (cnt > size)? size: cnt;
+
+	for (i = 0; i < cnt; i++)
+	{
+		txbuf_get(&val);
+		copy_to_user(buf+i, &val, 1);
+	}
+
+	return cnt;
+}
+
+static ssize_t virt_uart_buf_write (struct file *file, const char __user *buf, size_t size, loff_t *off)
+{
+	/* get data */
+	copy_from_user(rxbuf, buf, size);
+	rx_buf_w = size;
+
+	/* 模拟产生RX中断 */
+	irq_set_irqchip_state(virt_port->irq, IRQCHIP_STATE_PENDING, 1);
+	
+	return size;
+}
+
+static const struct file_operations virt_uart_buf_fops = {
+	.read		= virt_uart_buf_read,
+	.write		= virt_uart_buf_write,
+};
+
+
+static unsigned int virt_tx_empty(struct uart_port *port)
+{
+	/* 因为要发送的数据瞬间存入buffer */
+	return 1;
+}
+
+
+/*
+ * interrupts disabled on entry
+ */
+static void virt_start_tx(struct uart_port *port)
+{
+	struct circ_buf *xmit = &port->state->xmit;
+
+	while (!uart_circ_empty(xmit) &&
+	       !uart_tx_stopped(port)) {
+		/* send xmit->buf[xmit->tail]
+		 * out the port here */
+
+		/* 把circ buffer中的数据全部存入txbuf */
+
+		//txbuf[tx_buf_w++] =  xmit->buf[xmit->tail];
+		txbuf_put(xmit->buf[xmit->tail]);
+		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
+		port->icount.tx++;
+	}
+
+   if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	   uart_write_wakeup(port);
+
+}
+
+static void
+virt_set_termios(struct uart_port *port, struct ktermios *termios,
+		   struct ktermios *old)
+{
+	return;
+}
+
+static const struct uart_ops virt_pops = {
+	.tx_empty	= virt_tx_empty,
+	//.set_mctrl	= imx_set_mctrl,
+	//.get_mctrl	= imx_get_mctrl,
+	//.stop_tx	= imx_stop_tx,
+	.start_tx	= virt_start_tx,
+	//.stop_rx	= imx_stop_rx,
+	//.enable_ms	= imx_enable_ms,
+	//.break_ctl	= imx_break_ctl,
+	//.startup	= imx_startup,
+	//.shutdown	= imx_shutdown,
+	//.flush_buffer	= imx_flush_buffer,
+	.set_termios	= virt_set_termios,
+	//.type		= imx_type,
+	//.config_port	= imx_config_port,
+	//.verify_port	= imx_verify_port,
+};
+
+
+static irqreturn_t virt_uart_rxint(int irq, void *dev_id)
+{
+	struct uart_port *port = dev_id;
+	unsigned long flags;
+	int i;
+	
+	spin_lock_irqsave(&port->lock, flags);
+
+	for (i = 0; i < rx_buf_w; i++) {
+		port->icount.rx++;
+	
+		/* get data from hardware/rxbuf */
+
+		/* put data to ldisc */
+		tty_insert_flip_char(port, rxbuf[i], TTY_NORMAL)
+	}
+	rx_buf_w = 0;
+
+	spin_unlock_irqrestore(&port->lock, flags);
+	tty_flip_buffer_push(port);
+	
+	return IRQ_HANDLED;
+}
+
+
+static int virtual_uart_probe(struct platform_device *pdev)
+{	
+	int rxirq;
+	int ret;
+
+	/* create proc file */	
+	uart_proc_file = proc_create("virt_uart_buf", 0, NULL, &virt_uart_buf_fops);
+	
+	//uart_add_one_port(struct uart_driver * drv, struct uart_port * uport);
+
+	/* 从设备树获得硬件信息 */
+	rxirq = platform_get_irq(pdev, 0);
+	ret = devm_request_irq(&pdev->dev, rxirq, virt_uart_rxint, 0,
+				   dev_name(&pdev->dev), virt_port);
+	
+	/* 分配设置注册uart_port */
+	virt_port = devm_kzalloc(&pdev->dev, sizeof(*virt_port), GFP_KERNEL);
+
+	virt_port->dev = &pdev->dev;
+	virt_port->iotype = UPIO_MEM;
+	virt_port->irq = rxirq;
+	virt_port->fifosize = 32;
+	virt_port->ops = &virt_pops;
+	virt_port->flags = UPF_BOOT_AUTOCONF;
+	
+	return uart_add_one_port(&virt_uart_drv, virt_port);
+	
+}
+static int virtual_uart_remove(struct platform_device *pdev)
+{
+	proc_remove(uart_proc_file);
+	return 0;
+}
+
+
+
+static const struct of_device_id virtual_uart_of_match[] = {
+	{ .compatible = "100ask,virtual_uart", },
+	{ },
+};
+
+
+static struct platform_driver virtual_uart_driver = {
+	.probe		= virtual_uart_probe,
+	.remove		= virtual_uart_remove,
+	.driver		= {
+		.name	= "100ask_virtual_uart",
+		.of_match_table = of_match_ptr(virtual_uart_of_match),
+	}
+};
+
+
+/* 1. 入口函数 */
+static int __init virtual_uart_init(void)
+{	
+	printk("%s %s %d\n", __FILE__, __FUNCTION__, __LINE__);
+	
+	int ret = uart_register_driver(&virt_uart_drv);
+
+	if (ret)
+		return ret;
+	
+	/* 1.1 注册一个platform_driver */
+	return platform_driver_register(&virtual_uart_driver);
+}
+
+
+/* 2. 出口函数 */
+static void __exit virtual_uart_exit(void)
+{
+	printk("%s %s %d\n", __FILE__, __FUNCTION__, __LINE__);
+	/* 2.1 反注册platform_driver */
+	platform_driver_unregister(&virtual_uart_driver);
+}
+
+module_init(virtual_uart_init);
+module_exit(virtual_uart_exit);
+
+MODULE_LICENSE("GPL");
+
+
diff --git a/IMX6ULL/source/09_UART/06_virtual_uart_driver_txrx/virtual_uart.dts b/IMX6ULL/source/09_UART/06_virtual_uart_driver_txrx/virtual_uart.dts
new file mode 100644
index 0000000..50b380a
--- /dev/null
+++ b/IMX6ULL/source/09_UART/06_virtual_uart_driver_txrx/virtual_uart.dts
@@ -0,0 +1,13 @@
+
+
+/{
+	virtual_uart: virtual_uart_100ask {
+		compatible = "100ask,virtual_uart";
+		
+		interrupt-parent = <&intc>;
+		interrupts = <GIC_SPI 99 IRQ_TYPE_LEVEL_HIGH>;
+		
+	};
+	
+	
+};
diff --git a/IMX6ULL/source/09_UART/07_virtual_uart_driver_ok/Makefile b/IMX6ULL/source/09_UART/07_virtual_uart_driver_ok/Makefile
new file mode 100644
index 0000000..91e9a18
--- /dev/null
+++ b/IMX6ULL/source/09_UART/07_virtual_uart_driver_ok/Makefile
@@ -0,0 +1,20 @@
+
+# 1. 使用不同的开发板内核时, 一定要修改KERN_DIR
+# 2. KERN_DIR中的内核要事先配置、编译, 为了能编译内核, 要先设置下列环境变量:
+# 2.1 ARCH,          比如: export ARCH=arm64
+# 2.2 CROSS_COMPILE, 比如: export CROSS_COMPILE=aarch64-linux-gnu-
+# 2.3 PATH,          比如: export PATH=$PATH:/home/book/100ask_roc-rk3399-pc/ToolChain-6.3.1/gcc-linaro-6.3.1-2017.05-x86_64_aarch64-linux-gnu/bin 
+# 注意: 不同的开发板不同的编译器上述3个环境变量不一定相同,
+#       请参考各开发板的高级用户使用手册
+
+KERN_DIR = /home/book/100ask_imx6ull-sdk/Linux-4.9.88
+
+all:
+	make -C $(KERN_DIR) M=`pwd` modules 
+
+clean:
+	make -C $(KERN_DIR) M=`pwd` modules clean
+	rm -rf modules.order
+
+obj-m   += virtual_uart.o
+
diff --git a/IMX6ULL/source/09_UART/07_virtual_uart_driver_ok/virtual_uart.c b/IMX6ULL/source/09_UART/07_virtual_uart_driver_ok/virtual_uart.c
new file mode 100644
index 0000000..17a64dd
--- /dev/null
+++ b/IMX6ULL/source/09_UART/07_virtual_uart_driver_ok/virtual_uart.c
@@ -0,0 +1,334 @@
+#include <linux/module.h>
+#include <linux/ioport.h>
+#include <linux/init.h>
+#include <linux/console.h>
+#include <linux/sysrq.h>
+#include <linux/platform_device.h>
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
+#include <linux/serial_core.h>
+#include <linux/serial.h>
+#include <linux/clk.h>
+#include <linux/delay.h>
+#include <linux/rational.h>
+#include <linux/reset.h>
+#include <linux/slab.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/io.h>
+#include <linux/dma-mapping.h>
+#include <linux/proc_fs.h>
+
+#include <asm/irq.h>
+
+#define BUF_LEN  1024
+#define NEXT_PLACE(i) ((i+1)&0x3FF)
+
+static struct uart_port	*virt_port;
+static unsigned char txbuf[BUF_LEN];
+static int tx_buf_r = 0;
+static int tx_buf_w = 0;
+
+static unsigned char rxbuf[BUF_LEN];
+static int rx_buf_w = 0;
+
+static struct proc_dir_entry *uart_proc_file;
+
+
+static struct uart_driver virt_uart_drv = {
+	.owner          = THIS_MODULE,
+	.driver_name    = "VIRT_UART",
+	.dev_name       = "ttyVIRT",
+	.major          = 0,
+	.minor          = 0,
+	.nr             = 1,
+};
+
+
+/* circle buffer */
+
+
+static int is_txbuf_empty(void)
+{
+	return tx_buf_r == tx_buf_w;
+}
+
+static int is_txbuf_full(void)
+{
+	return NEXT_PLACE(tx_buf_w) == tx_buf_r;
+}
+
+static int txbuf_put(unsigned char val)
+{
+	if (is_txbuf_full())
+		return -1;
+	txbuf[tx_buf_w] = val;
+	tx_buf_w = NEXT_PLACE(tx_buf_w);
+	return 0;
+}
+
+static int txbuf_get(unsigned char *pval)
+{
+	if (is_txbuf_empty())
+		return -1;
+	*pval = txbuf[tx_buf_r];
+	tx_buf_r = NEXT_PLACE(tx_buf_r);
+	return 0;
+}
+
+static int txbuf_count(void)
+{
+	if (tx_buf_w >= tx_buf_r)
+		return tx_buf_w - tx_buf_r;
+	else
+		return BUF_LEN + tx_buf_w - tx_buf_r;
+}
+
+
+
+ssize_t virt_uart_buf_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
+{
+	/* 把txbuf中的数据copy_to_user */
+	int cnt = txbuf_count();
+	int i;
+	unsigned char val;
+	int ret;
+
+	cnt = (cnt > size)? size: cnt;
+
+	for (i = 0; i < cnt; i++)
+	{
+		txbuf_get(&val);
+		ret = copy_to_user(buf+i, &val, 1);
+	}
+
+	return cnt;
+}
+
+static ssize_t virt_uart_buf_write (struct file *file, const char __user *buf, size_t size, loff_t *off)
+{
+	int ret;
+	
+	/* get data */
+	ret = copy_from_user(rxbuf, buf, size);
+	rx_buf_w = size;
+
+	/* 模拟产生RX中断 */
+	irq_set_irqchip_state(virt_port->irq, IRQCHIP_STATE_PENDING, 1);
+	
+	return size;
+}
+
+static const struct file_operations virt_uart_buf_fops = {
+	.read		= virt_uart_buf_read,
+	.write		= virt_uart_buf_write,
+};
+
+
+static unsigned int virt_tx_empty(struct uart_port *port)
+{
+	/* 因为要发送的数据瞬间存入buffer */
+	return 1;
+}
+
+
+/*
+ * interrupts disabled on entry
+ */
+static void virt_start_tx(struct uart_port *port)
+{
+	struct circ_buf *xmit = &port->state->xmit;
+
+	while (!uart_circ_empty(xmit) &&
+	       !uart_tx_stopped(port)) {
+		/* send xmit->buf[xmit->tail]
+		 * out the port here */
+
+		/* 把circ buffer中的数据全部存入txbuf */
+
+		//txbuf[tx_buf_w++] =  xmit->buf[xmit->tail];
+		txbuf_put(xmit->buf[xmit->tail]);
+		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
+		port->icount.tx++;
+	}
+
+   if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	   uart_write_wakeup(port);
+
+}
+
+
+static void
+virt_set_termios(struct uart_port *port, struct ktermios *termios,
+		  struct ktermios *old)
+{
+   return;
+}
+
+static int virt_startup(struct uart_port *port)
+{
+   return 0;
+}
+
+static void virt_set_mctrl(struct uart_port *port, unsigned int mctrl)
+{
+}
+
+static unsigned int virt_get_mctrl(struct uart_port *port)
+{
+   return 0;
+}
+
+static void virt_stop_tx(struct uart_port *port)
+{
+}
+
+static void virt_stop_rx(struct uart_port *port)
+{
+}
+
+static void virt_shutdown(struct uart_port *port)
+{
+}
+
+static const char *virt_type(struct uart_port *port)
+{
+   return "100ASK_VIRT_UART";
+}
+
+
+static const struct uart_ops virt_pops = {
+   .tx_empty   = virt_tx_empty,
+   .set_mctrl  = virt_set_mctrl,
+   .get_mctrl  = virt_get_mctrl,
+   .stop_tx    = virt_stop_tx,
+   .start_tx   = virt_start_tx,
+   .stop_rx    = virt_stop_rx,
+   //.enable_ms    = imx_enable_ms,
+   //.break_ctl    = imx_break_ctl,
+   .startup    = virt_startup,
+   .shutdown   = virt_shutdown,
+   //.flush_buffer = imx_flush_buffer,
+   .set_termios    = virt_set_termios,
+   .type	   = virt_type,
+   //.config_port  = imx_config_port,
+   //.verify_port  = imx_verify_port,
+};
+
+
+
+static irqreturn_t virt_uart_rxint(int irq, void *dev_id)
+{
+	struct uart_port *port = dev_id;
+	struct tty_port *tport = &port->state->port;
+	unsigned long flags;
+	int i;
+	
+	spin_lock_irqsave(&port->lock, flags);
+
+	for (i = 0; i < rx_buf_w; i++) {
+		port->icount.rx++;
+	
+		/* get data from hardware/rxbuf */
+
+		/* put data to ldisc */
+		tty_insert_flip_char(tport, rxbuf[i], TTY_NORMAL);
+	}
+	rx_buf_w = 0;
+
+	spin_unlock_irqrestore(&port->lock, flags);
+	tty_flip_buffer_push(tport);
+	
+	return IRQ_HANDLED;
+}
+
+
+static int virtual_uart_probe(struct platform_device *pdev)
+{	
+	int rxirq;
+	int ret;
+
+	/* create proc file */	
+	uart_proc_file = proc_create("virt_uart_buf", 0, NULL, &virt_uart_buf_fops);
+	
+	//uart_add_one_port(struct uart_driver * drv, struct uart_port * uport);
+
+	/* 从设备树获得硬件信息 */
+	rxirq = platform_get_irq(pdev, 0);
+	
+	/* 分配设置注册uart_port */
+	virt_port = devm_kzalloc(&pdev->dev, sizeof(*virt_port), GFP_KERNEL);
+
+	virt_port->dev = &pdev->dev;
+	virt_port->iotype = UPIO_MEM;
+	virt_port->irq = rxirq;
+	virt_port->fifosize = 32;
+	virt_port->ops = &virt_pops;
+	virt_port->flags = UPF_BOOT_AUTOCONF;
+	virt_port->type = PORT_8250;
+
+	ret = devm_request_irq(&pdev->dev, rxirq, virt_uart_rxint, 0,
+				   dev_name(&pdev->dev), virt_port);
+	
+	return uart_add_one_port(&virt_uart_drv, virt_port);
+	
+}
+static int virtual_uart_remove(struct platform_device *pdev)
+{
+	uart_remove_one_port(&virt_uart_drv, virt_port);
+	proc_remove(uart_proc_file);
+	return 0;
+}
+
+
+
+static const struct of_device_id virtual_uart_of_match[] = {
+	{ .compatible = "100ask,virtual_uart", },
+	{ },
+};
+
+
+static struct platform_driver virtual_uart_driver = {
+	.probe		= virtual_uart_probe,
+	.remove		= virtual_uart_remove,
+	.driver		= {
+		.name	= "100ask_virtual_uart",
+		.of_match_table = of_match_ptr(virtual_uart_of_match),
+	}
+};
+
+
+/* 1. 入口函数 */
+static int __init virtual_uart_init(void)
+{	
+	int ret;
+
+	printk("%s %s %d\n", __FILE__, __FUNCTION__, __LINE__);
+	
+	ret = uart_register_driver(&virt_uart_drv);
+
+	if (ret)
+		return ret;
+	
+	/* 1.1 注册一个platform_driver */
+	return platform_driver_register(&virtual_uart_driver);
+}
+
+
+/* 2. 出口函数 */
+static void __exit virtual_uart_exit(void)
+{
+	printk("%s %s %d\n", __FILE__, __FUNCTION__, __LINE__);
+	/* 2.1 反注册platform_driver */
+	platform_driver_unregister(&virtual_uart_driver);
+
+	
+	uart_unregister_driver(&virt_uart_drv);
+}
+
+module_init(virtual_uart_init);
+module_exit(virtual_uart_exit);
+
+MODULE_LICENSE("GPL");
+
+
diff --git a/IMX6ULL/source/09_UART/07_virtual_uart_driver_ok/virtual_uart.dts b/IMX6ULL/source/09_UART/07_virtual_uart_driver_ok/virtual_uart.dts
new file mode 100644
index 0000000..50b380a
--- /dev/null
+++ b/IMX6ULL/source/09_UART/07_virtual_uart_driver_ok/virtual_uart.dts
@@ -0,0 +1,13 @@
+
+
+/{
+	virtual_uart: virtual_uart_100ask {
+		compatible = "100ask,virtual_uart";
+		
+		interrupt-parent = <&intc>;
+		interrupts = <GIC_SPI 99 IRQ_TYPE_LEVEL_HIGH>;
+		
+	};
+	
+	
+};
diff --git a/README.md b/README.md
index 464f300..c2efe8a 100644
--- a/README.md
+++ b/README.md
@@ -367,6 +367,18 @@ git clone https://e.coding.net/weidongshan/linux/doc_and_source_for_drivers.git
   14_编写虚拟UART驱动程序_实现uart_ops
   ```
 
+* 2021.08.04 发布"UART子系统"
+
+  ```shell
+  15_编写虚拟UART驱动程序_实现数据传输
+  ```
+* 2021.08.06 发布"UART子系统"
+
+  ```shell
+  16_编写虚拟UART驱动程序_调试
+  ```
+
+
 ## 6. 联系方式
 
 * 官网：http://www.100ask.net
diff --git a/STM32MP157/doc_pic/09_UART/15_编写虚拟UART驱动程序_实现数据传输.md b/STM32MP157/doc_pic/09_UART/15_编写虚拟UART驱动程序_实现数据传输.md
new file mode 100644
index 0000000..d36bc34
--- /dev/null
+++ b/STM32MP157/doc_pic/09_UART/15_编写虚拟UART驱动程序_实现数据传输.md
@@ -0,0 +1,136 @@
+## 编写虚拟UART驱动程序\_实现数据传输
+
+* 参考代码
+
+  ```shell
+  硬件相关：
+  drivers/tty/serial/imx.c
+  drivers/tty/serial/stm32-usart.c
+  
+  串口核心层：
+  drivers/tty/serial/serial_core.c
+  
+  TTY层:
+  drivers/tty/tty_io.c
+  ```
+
+  
+
+* 本节课程源码在GIT仓库里
+
+  ```shell
+  doc_and_source_for_drivers\IMX6ULL\source\09_UART
+  	06_virtual_uart_driver_txrx
+  doc_and_source_for_drivers\STM32MP157\source\A7\09_UART
+  	06_virtual_uart_driver_txrx
+  ```
+  
+  
+
+### 1. 虚拟UART的驱动组成
+
+![image-20210730142813809](pic/09_UART/39_uart_driver.png)
+
+
+
+### 2. 虚拟UART的数据流程
+
+![image-20210730150445225](pic/09_UART/40_virtual_uart.png)
+
+为了做实验，我们还要创建一个虚拟文件：/proc/virt_uart_buf
+
+* 要发数据给虚拟串口时，执行：echo "xxx" > /proc/virt_uart_buf
+* 要读取虚拟串口的数据时，执行：cat /proc/virt_uart_buf
+
+
+
+### 3. 实现/proc文件
+
+参考`/proc/cmdline`，怎么找到它对应的驱动？在Linux内核源码下执行以下命令搜索：
+
+```shell
+grep "cmdline" * -nr | grep proc
+```
+
+得到：
+
+```shell
+fs/proc/cmdline.c:26:   proc_create("cmdline", 0, NULL, &cmdline_proc_fops);
+```
+
+
+
+### 4. 触发中断
+
+使用如下函数：
+
+```c
+int irq_set_irqchip_state(unsigned int irq, enum irqchip_irq_state which,
+			  bool val);
+```
+
+怎么找到它的？在中断子系统中，我们知道往GIC寄存器GICD_ISPENDRn写入某一位就可以触发中断。内核代码中怎么访问这些寄存器？
+在`drivers\irqchip\irq-gic.c`中可以看到irq_chip中的"irq_set_irqchip_state"被用来设置中断状态：
+
+```c
+static struct irq_chip gic_chip = {
+	.irq_mask		= gic_mask_irq,
+	.irq_unmask		= gic_unmask_irq,
+	.irq_eoi		= gic_eoi_irq,
+	.irq_set_type		= gic_set_type,
+	.irq_get_irqchip_state	= gic_irq_get_irqchip_state,
+	.irq_set_irqchip_state	= gic_irq_set_irqchip_state, /* 2. 继续搜"irq_set_irqchip_state" */
+	.flags			= IRQCHIP_SET_TYPE_MASKED |
+				  IRQCHIP_SKIP_SET_WAKE |
+				  IRQCHIP_MASK_ON_SUSPEND,
+};
+
+static int gic_irq_set_irqchip_state(struct irq_data *d,
+				     enum irqchip_irq_state which, bool val)
+{
+	u32 reg;
+
+	switch (which) {
+	case IRQCHIP_STATE_PENDING:
+		reg = val ? GIC_DIST_PENDING_SET : GIC_DIST_PENDING_CLEAR; /* 1. 找到寄存器 */
+		break;
+
+	case IRQCHIP_STATE_ACTIVE:
+		reg = val ? GIC_DIST_ACTIVE_SET : GIC_DIST_ACTIVE_CLEAR;
+		break;
+
+	case IRQCHIP_STATE_MASKED:
+		reg = val ? GIC_DIST_ENABLE_CLEAR : GIC_DIST_ENABLE_SET;
+		break;
+
+	default:
+		return -EINVAL;
+	}
+
+	gic_poke_irq(d, reg);
+	return 0;
+}
+```
+
+
+
+继续搜"irq_set_irqchip_state"，在`drivers\irqchip\irq-gic.c`中可以看到：
+
+```c
+int irq_set_irqchip_state(unsigned int irq, enum irqchip_irq_state which,
+			  bool val)
+{
+    ......
+}
+
+EXPORT_SYMBOL_GPL(irq_set_irqchip_state);
+```
+
+
+
+以后就可与使用如下代码触发某个中断：
+
+```c
+irq_set_irqchip_state(irq, IRQCHIP_STATE_PENDING, 1);
+```
+
diff --git a/STM32MP157/doc_pic/09_UART/15_编写虚拟UART驱动程序_实现数据传输.tif b/STM32MP157/doc_pic/09_UART/15_编写虚拟UART驱动程序_实现数据传输.tif
new file mode 100644
index 0000000..7333f25
Binary files /dev/null and b/STM32MP157/doc_pic/09_UART/15_编写虚拟UART驱动程序_实现数据传输.tif differ
diff --git a/STM32MP157/doc_pic/09_UART/16_编写虚拟UART驱动程序_调试.md b/STM32MP157/doc_pic/09_UART/16_编写虚拟UART驱动程序_调试.md
new file mode 100644
index 0000000..0a75d98
--- /dev/null
+++ b/STM32MP157/doc_pic/09_UART/16_编写虚拟UART驱动程序_调试.md
@@ -0,0 +1,211 @@
+## 编写虚拟UART驱动程序_调试
+
+* 参考代码
+
+  ```shell
+  硬件相关：
+  drivers/tty/serial/imx.c
+  drivers/tty/serial/stm32-usart.c
+  
+  串口核心层：
+  drivers/tty/serial/serial_core.c
+  
+  TTY层:
+  drivers/tty/tty_io.c
+  ```
+
+  
+
+* 本节课程源码在GIT仓库里
+
+  ```shell
+  doc_and_source_for_drivers\IMX6ULL\source\09_UART
+  	07_virtual_uart_driver_ok
+  doc_and_source_for_drivers\STM32MP157\source\A7\09_UART
+  	07_virtual_uart_driver_ok
+  ```
+  
+
+
+
+### 1. 实验流程
+
+![image-20210806120309603](pic/09_UART/41_data_flow.png)
+
+
+
+### 2. 上机实验
+
+#### 2.1 设置工具链
+
+##### 1. STM32MP157
+
+  ```shell
+  export ARCH=arm
+  export CROSS_COMPILE=arm-buildroot-linux-gnueabihf-
+  export PATH=$PATH:/home/book/100ask_stm32mp157_pro-sdk/ToolChain/arm-buildroot-linux-gnueabihf_sdk-buildroot/bin
+  ```
+
+##### 2. IMX6ULL
+
+  ```shell
+  export ARCH=arm
+  export CROSS_COMPILE=arm-linux-gnueabihf-
+  export PATH=$PATH:/home/book/100ask_imx6ull-sdk/ToolChain/gcc-linaro-6.2.1-2016.11-x86_64_arm-linux-gnueabihf/bin
+  ```
+
+
+
+#### 2.2 编译、替换设备树
+
+##### 1. STM32MP157
+
+  * 修改`arch/arm/boot/dts/stm32mp157c-100ask-512d-lcd-v1.dts`，添加如下代码：
+
+    ```shell
+    / {
+    	virtual_uart: virtual_uart_100ask {
+    		compatible = "100ask,virtual_uart";
+    		
+    		interrupt-parent = <&intc>;
+    		interrupts = <GIC_SPI 99 IRQ_TYPE_LEVEL_HIGH>;
+    		
+    	};
+    };
+    ```
+
+    
+
+  * 编译设备树：
+    在Ubuntu的STM32MP157内核目录下执行如下命令,
+    得到设备树文件：`arch/arm/boot/dts/stm32mp157c-100ask-512d-lcd-v2.dtb`
+
+    ```shell
+    make dtbs
+    ```
+
+  * 复制到NFS目录：
+
+    ```shell
+    $ cp arch/arm/boot/dts/stm32mp157c-100ask-512d-lcd-v2.dtb ~/nfs_rootfs/
+    ```
+
+  * 开发板上挂载NFS文件系统
+
+    * vmware使用NAT(假设windowsIP为192.168.2.100)
+
+      ```shell
+      [root@100ask:~]# mount -t nfs -o nolock,vers=3,port=2049,mountport=9999 
+      192.168.2.100:/home/book/nfs_rootfs /mnt
+      ```
+
+    * vmware使用桥接，或者不使用vmware而是直接使用服务器：假设Ubuntu IP为192.168.2.137
+
+      ```shell
+      [root@100ask:~]#  mount -t nfs -o nolock,vers=3 192.168.2.137:/home/book/nfs_rootfs /mnt
+      ```
+
+* 更新设备树
+
+  ```shell
+  [root@100ask:~]# mount  /dev/mmcblk2p2  /boot
+  [root@100ask:~]# cp /mnt/stm32mp157c-100ask-512d-lcd-v1.dtb /boot
+  [root@100ask:~]# sync
+  ```
+
+* 重启开发板
+
+  
+
+
+
+##### 2. IMX6ULL
+
+  * 修改`arch/arm/boot/dts/100ask_imx6ull-14x14.dts`，添加如下代码：
+
+    ```shell
+    / {
+    	virtual_uart: virtual_uart_100ask {
+    		compatible = "100ask,virtual_uart";
+    		
+    		interrupt-parent = <&intc>;
+    		interrupts = <GIC_SPI 99 IRQ_TYPE_LEVEL_HIGH>;
+    		
+    	};
+    
+    };
+    ```
+
+    
+
+  * 编译设备树：
+    在Ubuntu的IMX6ULL内核目录下执行如下命令,
+    得到设备树文件：`arch/arm/boot/dts/100ask_imx6ull-14x14.dtb`
+
+    ```shell
+    make dtbs
+    ```
+
+  * 复制到NFS目录：
+
+    ```shell
+    $ cp arch/arm/boot/dts/100ask_imx6ull-14x14.dtb ~/nfs_rootfs/
+    ```
+
+* 开发板上挂载NFS文件系统
+
+  * vmware使用NAT(假设windowsIP为192.168.2.100)
+
+    ```shell
+    [root@100ask:~]# mount -t nfs -o nolock,vers=3,port=2049,mountport=9999 
+    192.168.2.100:/home/book/nfs_rootfs /mnt
+    ```
+
+  * vmware使用桥接，或者不使用vmware而是直接使用服务器：假设Ubuntu IP为192.168.2.137
+
+    ```shell
+    [root@100ask:~]#  mount -t nfs -o nolock,vers=3 192.168.2.137:/home/book/nfs_rootfs /mnt
+    ```
+
+  * 更新设备树
+
+    ```shell
+    [root@100ask:~]# cp /mnt/100ask_imx6ull-14x14.dtb /boot
+    [root@100ask:~]# sync
+    ```
+
+* 重启开发板
+
+
+
+#### 2.3 编译、安装驱动程序
+
+* 编译：
+
+  * 在Ubuntu上
+  * 修改`07_virtual_uart_driver_ok`中的Makefile，指定内核路径`KERN_DIR`，在执行`make`命令即可。
+
+* 安装：
+
+  * 在开发板上
+
+  * 挂载NFS，复制文件，insmod，类似如下命令：
+
+    ```shell
+    mount -t nfs -o nolock,vers=3 192.168.2.137:/home/book/nfs_rootfs /mnt
+    // 对于IMX6ULL，想看到驱动打印信息，需要先执行
+    echo "7 4 1 7" > /proc/sys/kernel/printk
+    
+    insmod -f /mnt/virtual_uart.ko
+    
+    ```
+
+* 观察内核打印的信息
+
+
+
+### 3. 调试
+
+根据框架、数据流程来调试：
+
+![](pic/09_UART/24_tty_driver_level_2.png)
\ No newline at end of file
diff --git a/STM32MP157/doc_pic/09_UART/16_编写虚拟UART驱动程序_调试.tif b/STM32MP157/doc_pic/09_UART/16_编写虚拟UART驱动程序_调试.tif
new file mode 100644
index 0000000..3a62339
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diff --git a/STM32MP157/doc_pic/09_UART/pic/09_UART/41_data_flow.png b/STM32MP157/doc_pic/09_UART/pic/09_UART/41_data_flow.png
new file mode 100644
index 0000000..4bcd220
Binary files /dev/null and b/STM32MP157/doc_pic/09_UART/pic/09_UART/41_data_flow.png differ
diff --git a/STM32MP157/source/A7/09_UART/06_virtual_uart_driver_txrx/virtual_uart.c b/STM32MP157/source/A7/09_UART/06_virtual_uart_driver_txrx/virtual_uart.c
new file mode 100644
index 0000000..e52a0bf
--- /dev/null
+++ b/STM32MP157/source/A7/09_UART/06_virtual_uart_driver_txrx/virtual_uart.c
@@ -0,0 +1,288 @@
+#include <linux/module.h>
+#include <linux/ioport.h>
+#include <linux/init.h>
+#include <linux/console.h>
+#include <linux/sysrq.h>
+#include <linux/platform_device.h>
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
+#include <linux/serial_core.h>
+#include <linux/serial.h>
+#include <linux/clk.h>
+#include <linux/delay.h>
+#include <linux/rational.h>
+#include <linux/reset.h>
+#include <linux/slab.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/io.h>
+#include <linux/dma-mapping.h>
+
+#include <asm/irq.h>
+
+#define BUF_LEN  1024
+#define NEXT_PLACE(i) ((i+1)&0x3FF)
+
+static struct uart_port	*virt_port;
+static unsigned char txbuf[BUF_LEN];
+static int tx_buf_r = 0;
+static int tx_buf_w = 0;
+
+static unsigned char rxbuf[BUF_LEN];
+static int rx_buf_r = 0;
+static int rx_buf_w = 0;
+
+static struct proc_dir_entry *uart_proc_file;
+
+
+static struct uart_driver virt_uart_drv = {
+	.owner          = THIS_MODULE,
+	.driver_name    = "VIRT_UART",
+	.dev_name       = "ttyVIRT",
+	.major          = 0,
+	.minor          = 0,
+	.nr             = 1,
+};
+
+
+/* circle buffer */
+
+
+static int is_txbuf_empty(void)
+{
+	return tx_buf_r == tx_buf_w;
+}
+
+static int is_txbuf_full(void)
+{
+	return NEXT_PLACE(tx_buf_w) == tx_buf_r;
+}
+
+static int txbuf_put(unsigned char val)
+{
+	if (is_txbuf_full())
+		return -1;
+	txbuf[tx_buf_w] = val;
+	tx_buf_w = NEXT_PLACE(tx_buf_w);
+	return 0;
+}
+
+static int txbuf_get(unsigned char *pval)
+{
+	if (is_txbuf_empty())
+		return -1;
+	*pval = g_events[tx_buf_r];
+	tx_buf_r = NEXT_PLACE(tx_buf_r);
+	return 0;
+}
+
+static int txbuf_count(void)
+{
+	if (tx_buf_w >= tx_buf_r)
+		return tx_buf_w - tx_buf_r;
+	else
+		return BUF_LEN + tx_buf_w - tx_buf_r;
+}
+
+
+
+ssize_t virt_uart_buf_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
+{
+	/* 把txbuf中的数据copy_to_user */
+	int cnt = txbuf_count();
+	int i;
+	unsigned char val;
+
+	cnt = (cnt > size)? size: cnt;
+
+	for (i = 0; i < cnt; i++)
+	{
+		txbuf_get(&val);
+		copy_to_user(buf+i, &val, 1);
+	}
+
+	return cnt;
+}
+
+static ssize_t virt_uart_buf_write (struct file *file, const char __user *buf, size_t size, loff_t *off)
+{
+	/* get data */
+	copy_from_user(rxbuf, buf, size);
+	rx_buf_w = size;
+
+	/* 模拟产生RX中断 */
+	irq_set_irqchip_state(virt_port->irq, IRQCHIP_STATE_PENDING, 1);
+	
+	return size;
+}
+
+static const struct file_operations virt_uart_buf_fops = {
+	.read		= virt_uart_buf_read,
+	.write		= virt_uart_buf_write,
+};
+
+
+static unsigned int virt_tx_empty(struct uart_port *port)
+{
+	/* 因为要发送的数据瞬间存入buffer */
+	return 1;
+}
+
+
+/*
+ * interrupts disabled on entry
+ */
+static void virt_start_tx(struct uart_port *port)
+{
+	struct circ_buf *xmit = &port->state->xmit;
+
+	while (!uart_circ_empty(xmit) &&
+	       !uart_tx_stopped(port)) {
+		/* send xmit->buf[xmit->tail]
+		 * out the port here */
+
+		/* 把circ buffer中的数据全部存入txbuf */
+
+		//txbuf[tx_buf_w++] =  xmit->buf[xmit->tail];
+		txbuf_put(xmit->buf[xmit->tail]);
+		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
+		port->icount.tx++;
+	}
+
+   if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	   uart_write_wakeup(port);
+
+}
+
+static void
+virt_set_termios(struct uart_port *port, struct ktermios *termios,
+		   struct ktermios *old)
+{
+	return;
+}
+
+static const struct uart_ops virt_pops = {
+	.tx_empty	= virt_tx_empty,
+	//.set_mctrl	= imx_set_mctrl,
+	//.get_mctrl	= imx_get_mctrl,
+	//.stop_tx	= imx_stop_tx,
+	.start_tx	= virt_start_tx,
+	//.stop_rx	= imx_stop_rx,
+	//.enable_ms	= imx_enable_ms,
+	//.break_ctl	= imx_break_ctl,
+	//.startup	= imx_startup,
+	//.shutdown	= imx_shutdown,
+	//.flush_buffer	= imx_flush_buffer,
+	.set_termios	= virt_set_termios,
+	//.type		= imx_type,
+	//.config_port	= imx_config_port,
+	//.verify_port	= imx_verify_port,
+};
+
+
+static irqreturn_t virt_uart_rxint(int irq, void *dev_id)
+{
+	struct uart_port *port = dev_id;
+	unsigned long flags;
+	int i;
+	
+	spin_lock_irqsave(&port->lock, flags);
+
+	for (i = 0; i < rx_buf_w; i++) {
+		port->icount.rx++;
+	
+		/* get data from hardware/rxbuf */
+
+		/* put data to ldisc */
+		tty_insert_flip_char(port, rxbuf[i], TTY_NORMAL)
+	}
+	rx_buf_w = 0;
+
+	spin_unlock_irqrestore(&port->lock, flags);
+	tty_flip_buffer_push(port);
+	
+	return IRQ_HANDLED;
+}
+
+
+static int virtual_uart_probe(struct platform_device *pdev)
+{	
+	int rxirq;
+	int ret;
+
+	/* create proc file */	
+	uart_proc_file = proc_create("virt_uart_buf", 0, NULL, &virt_uart_buf_fops);
+	
+	//uart_add_one_port(struct uart_driver * drv, struct uart_port * uport);
+
+	/* 从设备树获得硬件信息 */
+	rxirq = platform_get_irq(pdev, 0);
+	ret = devm_request_irq(&pdev->dev, rxirq, virt_uart_rxint, 0,
+				   dev_name(&pdev->dev), virt_port);
+	
+	/* 分配设置注册uart_port */
+	virt_port = devm_kzalloc(&pdev->dev, sizeof(*virt_port), GFP_KERNEL);
+
+	virt_port->dev = &pdev->dev;
+	virt_port->iotype = UPIO_MEM;
+	virt_port->irq = rxirq;
+	virt_port->fifosize = 32;
+	virt_port->ops = &virt_pops;
+	virt_port->flags = UPF_BOOT_AUTOCONF;
+	
+	return uart_add_one_port(&virt_uart_drv, virt_port);
+	
+}
+static int virtual_uart_remove(struct platform_device *pdev)
+{
+	proc_remove(uart_proc_file);
+	return 0;
+}
+
+
+
+static const struct of_device_id virtual_uart_of_match[] = {
+	{ .compatible = "100ask,virtual_uart", },
+	{ },
+};
+
+
+static struct platform_driver virtual_uart_driver = {
+	.probe		= virtual_uart_probe,
+	.remove		= virtual_uart_remove,
+	.driver		= {
+		.name	= "100ask_virtual_uart",
+		.of_match_table = of_match_ptr(virtual_uart_of_match),
+	}
+};
+
+
+/* 1. 入口函数 */
+static int __init virtual_uart_init(void)
+{	
+	printk("%s %s %d\n", __FILE__, __FUNCTION__, __LINE__);
+	
+	int ret = uart_register_driver(&virt_uart_drv);
+
+	if (ret)
+		return ret;
+	
+	/* 1.1 注册一个platform_driver */
+	return platform_driver_register(&virtual_uart_driver);
+}
+
+
+/* 2. 出口函数 */
+static void __exit virtual_uart_exit(void)
+{
+	printk("%s %s %d\n", __FILE__, __FUNCTION__, __LINE__);
+	/* 2.1 反注册platform_driver */
+	platform_driver_unregister(&virtual_uart_driver);
+}
+
+module_init(virtual_uart_init);
+module_exit(virtual_uart_exit);
+
+MODULE_LICENSE("GPL");
+
+
diff --git a/STM32MP157/source/A7/09_UART/06_virtual_uart_driver_txrx/virtual_uart.dts b/STM32MP157/source/A7/09_UART/06_virtual_uart_driver_txrx/virtual_uart.dts
new file mode 100644
index 0000000..50b380a
--- /dev/null
+++ b/STM32MP157/source/A7/09_UART/06_virtual_uart_driver_txrx/virtual_uart.dts
@@ -0,0 +1,13 @@
+
+
+/{
+	virtual_uart: virtual_uart_100ask {
+		compatible = "100ask,virtual_uart";
+		
+		interrupt-parent = <&intc>;
+		interrupts = <GIC_SPI 99 IRQ_TYPE_LEVEL_HIGH>;
+		
+	};
+	
+	
+};
diff --git a/STM32MP157/source/A7/09_UART/07_virtual_uart_driver_ok/Makefile b/STM32MP157/source/A7/09_UART/07_virtual_uart_driver_ok/Makefile
new file mode 100644
index 0000000..2b6a3ad
--- /dev/null
+++ b/STM32MP157/source/A7/09_UART/07_virtual_uart_driver_ok/Makefile
@@ -0,0 +1,20 @@
+
+# 1. 使用不同的开发板内核时, 一定要修改KERN_DIR
+# 2. KERN_DIR中的内核要事先配置、编译, 为了能编译内核, 要先设置下列环境变量:
+# 2.1 ARCH,          比如: export ARCH=arm64
+# 2.2 CROSS_COMPILE, 比如: export CROSS_COMPILE=aarch64-linux-gnu-
+# 2.3 PATH,          比如: export PATH=$PATH:/home/book/100ask_roc-rk3399-pc/ToolChain-6.3.1/gcc-linaro-6.3.1-2017.05-x86_64_aarch64-linux-gnu/bin 
+# 注意: 不同的开发板不同的编译器上述3个环境变量不一定相同,
+#       请参考各开发板的高级用户使用手册
+
+KERN_DIR = /home/book/100ask_stm32mp157_pro-sdk/Linux-5.4
+
+all:
+	make -C $(KERN_DIR) M=`pwd` modules 
+
+clean:
+	make -C $(KERN_DIR) M=`pwd` modules clean
+	rm -rf modules.order
+
+obj-m   += virtual_uart.o
+
diff --git a/STM32MP157/source/A7/09_UART/07_virtual_uart_driver_ok/virtual_uart.c b/STM32MP157/source/A7/09_UART/07_virtual_uart_driver_ok/virtual_uart.c
new file mode 100644
index 0000000..17a64dd
--- /dev/null
+++ b/STM32MP157/source/A7/09_UART/07_virtual_uart_driver_ok/virtual_uart.c
@@ -0,0 +1,334 @@
+#include <linux/module.h>
+#include <linux/ioport.h>
+#include <linux/init.h>
+#include <linux/console.h>
+#include <linux/sysrq.h>
+#include <linux/platform_device.h>
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
+#include <linux/serial_core.h>
+#include <linux/serial.h>
+#include <linux/clk.h>
+#include <linux/delay.h>
+#include <linux/rational.h>
+#include <linux/reset.h>
+#include <linux/slab.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/io.h>
+#include <linux/dma-mapping.h>
+#include <linux/proc_fs.h>
+
+#include <asm/irq.h>
+
+#define BUF_LEN  1024
+#define NEXT_PLACE(i) ((i+1)&0x3FF)
+
+static struct uart_port	*virt_port;
+static unsigned char txbuf[BUF_LEN];
+static int tx_buf_r = 0;
+static int tx_buf_w = 0;
+
+static unsigned char rxbuf[BUF_LEN];
+static int rx_buf_w = 0;
+
+static struct proc_dir_entry *uart_proc_file;
+
+
+static struct uart_driver virt_uart_drv = {
+	.owner          = THIS_MODULE,
+	.driver_name    = "VIRT_UART",
+	.dev_name       = "ttyVIRT",
+	.major          = 0,
+	.minor          = 0,
+	.nr             = 1,
+};
+
+
+/* circle buffer */
+
+
+static int is_txbuf_empty(void)
+{
+	return tx_buf_r == tx_buf_w;
+}
+
+static int is_txbuf_full(void)
+{
+	return NEXT_PLACE(tx_buf_w) == tx_buf_r;
+}
+
+static int txbuf_put(unsigned char val)
+{
+	if (is_txbuf_full())
+		return -1;
+	txbuf[tx_buf_w] = val;
+	tx_buf_w = NEXT_PLACE(tx_buf_w);
+	return 0;
+}
+
+static int txbuf_get(unsigned char *pval)
+{
+	if (is_txbuf_empty())
+		return -1;
+	*pval = txbuf[tx_buf_r];
+	tx_buf_r = NEXT_PLACE(tx_buf_r);
+	return 0;
+}
+
+static int txbuf_count(void)
+{
+	if (tx_buf_w >= tx_buf_r)
+		return tx_buf_w - tx_buf_r;
+	else
+		return BUF_LEN + tx_buf_w - tx_buf_r;
+}
+
+
+
+ssize_t virt_uart_buf_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
+{
+	/* 把txbuf中的数据copy_to_user */
+	int cnt = txbuf_count();
+	int i;
+	unsigned char val;
+	int ret;
+
+	cnt = (cnt > size)? size: cnt;
+
+	for (i = 0; i < cnt; i++)
+	{
+		txbuf_get(&val);
+		ret = copy_to_user(buf+i, &val, 1);
+	}
+
+	return cnt;
+}
+
+static ssize_t virt_uart_buf_write (struct file *file, const char __user *buf, size_t size, loff_t *off)
+{
+	int ret;
+	
+	/* get data */
+	ret = copy_from_user(rxbuf, buf, size);
+	rx_buf_w = size;
+
+	/* 模拟产生RX中断 */
+	irq_set_irqchip_state(virt_port->irq, IRQCHIP_STATE_PENDING, 1);
+	
+	return size;
+}
+
+static const struct file_operations virt_uart_buf_fops = {
+	.read		= virt_uart_buf_read,
+	.write		= virt_uart_buf_write,
+};
+
+
+static unsigned int virt_tx_empty(struct uart_port *port)
+{
+	/* 因为要发送的数据瞬间存入buffer */
+	return 1;
+}
+
+
+/*
+ * interrupts disabled on entry
+ */
+static void virt_start_tx(struct uart_port *port)
+{
+	struct circ_buf *xmit = &port->state->xmit;
+
+	while (!uart_circ_empty(xmit) &&
+	       !uart_tx_stopped(port)) {
+		/* send xmit->buf[xmit->tail]
+		 * out the port here */
+
+		/* 把circ buffer中的数据全部存入txbuf */
+
+		//txbuf[tx_buf_w++] =  xmit->buf[xmit->tail];
+		txbuf_put(xmit->buf[xmit->tail]);
+		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
+		port->icount.tx++;
+	}
+
+   if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	   uart_write_wakeup(port);
+
+}
+
+
+static void
+virt_set_termios(struct uart_port *port, struct ktermios *termios,
+		  struct ktermios *old)
+{
+   return;
+}
+
+static int virt_startup(struct uart_port *port)
+{
+   return 0;
+}
+
+static void virt_set_mctrl(struct uart_port *port, unsigned int mctrl)
+{
+}
+
+static unsigned int virt_get_mctrl(struct uart_port *port)
+{
+   return 0;
+}
+
+static void virt_stop_tx(struct uart_port *port)
+{
+}
+
+static void virt_stop_rx(struct uart_port *port)
+{
+}
+
+static void virt_shutdown(struct uart_port *port)
+{
+}
+
+static const char *virt_type(struct uart_port *port)
+{
+   return "100ASK_VIRT_UART";
+}
+
+
+static const struct uart_ops virt_pops = {
+   .tx_empty   = virt_tx_empty,
+   .set_mctrl  = virt_set_mctrl,
+   .get_mctrl  = virt_get_mctrl,
+   .stop_tx    = virt_stop_tx,
+   .start_tx   = virt_start_tx,
+   .stop_rx    = virt_stop_rx,
+   //.enable_ms    = imx_enable_ms,
+   //.break_ctl    = imx_break_ctl,
+   .startup    = virt_startup,
+   .shutdown   = virt_shutdown,
+   //.flush_buffer = imx_flush_buffer,
+   .set_termios    = virt_set_termios,
+   .type	   = virt_type,
+   //.config_port  = imx_config_port,
+   //.verify_port  = imx_verify_port,
+};
+
+
+
+static irqreturn_t virt_uart_rxint(int irq, void *dev_id)
+{
+	struct uart_port *port = dev_id;
+	struct tty_port *tport = &port->state->port;
+	unsigned long flags;
+	int i;
+	
+	spin_lock_irqsave(&port->lock, flags);
+
+	for (i = 0; i < rx_buf_w; i++) {
+		port->icount.rx++;
+	
+		/* get data from hardware/rxbuf */
+
+		/* put data to ldisc */
+		tty_insert_flip_char(tport, rxbuf[i], TTY_NORMAL);
+	}
+	rx_buf_w = 0;
+
+	spin_unlock_irqrestore(&port->lock, flags);
+	tty_flip_buffer_push(tport);
+	
+	return IRQ_HANDLED;
+}
+
+
+static int virtual_uart_probe(struct platform_device *pdev)
+{	
+	int rxirq;
+	int ret;
+
+	/* create proc file */	
+	uart_proc_file = proc_create("virt_uart_buf", 0, NULL, &virt_uart_buf_fops);
+	
+	//uart_add_one_port(struct uart_driver * drv, struct uart_port * uport);
+
+	/* 从设备树获得硬件信息 */
+	rxirq = platform_get_irq(pdev, 0);
+	
+	/* 分配设置注册uart_port */
+	virt_port = devm_kzalloc(&pdev->dev, sizeof(*virt_port), GFP_KERNEL);
+
+	virt_port->dev = &pdev->dev;
+	virt_port->iotype = UPIO_MEM;
+	virt_port->irq = rxirq;
+	virt_port->fifosize = 32;
+	virt_port->ops = &virt_pops;
+	virt_port->flags = UPF_BOOT_AUTOCONF;
+	virt_port->type = PORT_8250;
+
+	ret = devm_request_irq(&pdev->dev, rxirq, virt_uart_rxint, 0,
+				   dev_name(&pdev->dev), virt_port);
+	
+	return uart_add_one_port(&virt_uart_drv, virt_port);
+	
+}
+static int virtual_uart_remove(struct platform_device *pdev)
+{
+	uart_remove_one_port(&virt_uart_drv, virt_port);
+	proc_remove(uart_proc_file);
+	return 0;
+}
+
+
+
+static const struct of_device_id virtual_uart_of_match[] = {
+	{ .compatible = "100ask,virtual_uart", },
+	{ },
+};
+
+
+static struct platform_driver virtual_uart_driver = {
+	.probe		= virtual_uart_probe,
+	.remove		= virtual_uart_remove,
+	.driver		= {
+		.name	= "100ask_virtual_uart",
+		.of_match_table = of_match_ptr(virtual_uart_of_match),
+	}
+};
+
+
+/* 1. 入口函数 */
+static int __init virtual_uart_init(void)
+{	
+	int ret;
+
+	printk("%s %s %d\n", __FILE__, __FUNCTION__, __LINE__);
+	
+	ret = uart_register_driver(&virt_uart_drv);
+
+	if (ret)
+		return ret;
+	
+	/* 1.1 注册一个platform_driver */
+	return platform_driver_register(&virtual_uart_driver);
+}
+
+
+/* 2. 出口函数 */
+static void __exit virtual_uart_exit(void)
+{
+	printk("%s %s %d\n", __FILE__, __FUNCTION__, __LINE__);
+	/* 2.1 反注册platform_driver */
+	platform_driver_unregister(&virtual_uart_driver);
+
+	
+	uart_unregister_driver(&virt_uart_drv);
+}
+
+module_init(virtual_uart_init);
+module_exit(virtual_uart_exit);
+
+MODULE_LICENSE("GPL");
+
+
diff --git a/STM32MP157/source/A7/09_UART/07_virtual_uart_driver_ok/virtual_uart.dts b/STM32MP157/source/A7/09_UART/07_virtual_uart_driver_ok/virtual_uart.dts
new file mode 100644
index 0000000..50b380a
--- /dev/null
+++ b/STM32MP157/source/A7/09_UART/07_virtual_uart_driver_ok/virtual_uart.dts
@@ -0,0 +1,13 @@
+
+
+/{
+	virtual_uart: virtual_uart_100ask {
+		compatible = "100ask,virtual_uart";
+		
+		interrupt-parent = <&intc>;
+		interrupts = <GIC_SPI 99 IRQ_TYPE_LEVEL_HIGH>;
+		
+	};
+	
+	
+};