diff --git a/IMX6ULL/doc_pic/09_UART/05_Linux串口应用编程.md b/IMX6ULL/doc_pic/09_UART/05_Linux串口应用编程.md
index e215879..313630b 100644
--- a/IMX6ULL/doc_pic/09_UART/05_Linux串口应用编程.md
+++ b/IMX6ULL/doc_pic/09_UART/05_Linux串口应用编程.md
@@ -97,7 +97,15 @@ export PATH=$PATH:/home/book/100ask_imx6ull-sdk/ToolChain/arm-buildroot-linux-gn
 
 
 
-编译、执行程序
+编译、执行程序:
+
+```shell
+1. Ubuntu上
+arm-buildroot-linux-gnueabihf-gcc -o serial_send_recv serial_send_recv.c
+
+2. 板子上
+/mnt/serial_send_recv  /dev/ttymxc5
+```
 
 
 
@@ -113,7 +121,17 @@ export PATH=$PATH:/home/book/100ask_stm32mp157_pro-sdk/ToolChain/arm-buildroot-l
 
 
 
-编译、执行程序
+编译、执行程序:
+
+```shell
+1. Ubuntu上
+arm-buildroot-linux-gnueabihf-gcc -o serial_send_recv serial_send_recv.c
+
+2. 板子上
+/mnt/serial_send_recv  /dev/ttySTM3
+```
+
+
 
 
 
@@ -211,7 +229,17 @@ export PATH=$PATH:/home/book/100ask_imx6ull-sdk/ToolChain/arm-buildroot-linux-gn
 
 
 
-编译、执行程序
+编译、执行程序:
+
+```shell
+1. Ubuntu上
+arm-buildroot-linux-gnueabihf-gcc -o gps_read gps_read.c
+
+2. 板子上
+/mnt/gps_read  /dev/ttymxc5
+```
+
+
 
 
 
@@ -227,7 +255,17 @@ export PATH=$PATH:/home/book/100ask_stm32mp157_pro-sdk/ToolChain/arm-buildroot-l
 
 
 
-编译、执行程序
+编译、执行程序：
+
+```shell
+1. Ubuntu上
+arm-buildroot-linux-gnueabihf-gcc -o gps_read gps_read.c
+
+2. 板子上
+/mnt/gps_read  /dev/ttySTM3
+```
+
+
 
 
 
diff --git a/IMX6ULL/doc_pic/09_UART/pic/09_UART/19_stm32mp157_extend_board_back.png b/IMX6ULL/doc_pic/09_UART/pic/09_UART/19_stm32mp157_extend_board_back.png
new file mode 100644
index 0000000..c418ab9
Binary files /dev/null and b/IMX6ULL/doc_pic/09_UART/pic/09_UART/19_stm32mp157_extend_board_back.png differ
diff --git a/IMX6ULL/doc_pic/09_UART/pic/09_UART/20_stm32mp157_pins_of_uart8.png b/IMX6ULL/doc_pic/09_UART/pic/09_UART/20_stm32mp157_pins_of_uart8.png
new file mode 100644
index 0000000..46d4a90
Binary files /dev/null and b/IMX6ULL/doc_pic/09_UART/pic/09_UART/20_stm32mp157_pins_of_uart8.png differ
diff --git a/IMX6ULL/doc_pic/09_UART/pic/09_UART/21_stm32mp157_uart8_pinctrl.png b/IMX6ULL/doc_pic/09_UART/pic/09_UART/21_stm32mp157_uart8_pinctrl.png
new file mode 100644
index 0000000..b88789b
Binary files /dev/null and b/IMX6ULL/doc_pic/09_UART/pic/09_UART/21_stm32mp157_uart8_pinctrl.png differ
diff --git a/IMX6ULL/source/09_UART/01_app_send_recv/serial_send_recv.c b/IMX6ULL/source/09_UART/01_app_send_recv/serial_send_recv.c
new file mode 100644
index 0000000..0e9bd29
--- /dev/null
+++ b/IMX6ULL/source/09_UART/01_app_send_recv/serial_send_recv.c
@@ -0,0 +1,177 @@
+#include <stdio.h>
+#include <string.h>
+#include <sys/types.h>
+#include <errno.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <termios.h>
+#include <stdlib.h>
+
+/* set_opt(fd,115200,8,'N',1) */
+int set_opt(int fd,int nSpeed, int nBits, char nEvent, int nStop)
+{
+	struct termios newtio,oldtio;
+	
+	if ( tcgetattr( fd,&oldtio) != 0) { 
+		perror("SetupSerial 1");
+		return -1;
+	}
+	
+	bzero( &newtio, sizeof( newtio ) );
+	newtio.c_cflag |= CLOCAL | CREAD; 
+	newtio.c_cflag &= ~CSIZE; 
+
+	newtio.c_lflag  &= ~(ICANON | ECHO | ECHOE | ISIG);  /*Input*/
+	newtio.c_oflag  &= ~OPOST;   /*Output*/
+
+	switch( nBits )
+	{
+	case 7:
+		newtio.c_cflag |= CS7;
+	break;
+	case 8:
+		newtio.c_cflag |= CS8;
+	break;
+	}
+
+	switch( nEvent )
+	{
+	case 'O':
+		newtio.c_cflag |= PARENB;
+		newtio.c_cflag |= PARODD;
+		newtio.c_iflag |= (INPCK | ISTRIP);
+	break;
+	case 'E': 
+		newtio.c_iflag |= (INPCK | ISTRIP);
+		newtio.c_cflag |= PARENB;
+		newtio.c_cflag &= ~PARODD;
+	break;
+	case 'N': 
+		newtio.c_cflag &= ~PARENB;
+	break;
+	}
+
+	switch( nSpeed )
+	{
+	case 2400:
+		cfsetispeed(&newtio, B2400);
+		cfsetospeed(&newtio, B2400);
+	break;
+	case 4800:
+		cfsetispeed(&newtio, B4800);
+		cfsetospeed(&newtio, B4800);
+	break;
+	case 9600:
+		cfsetispeed(&newtio, B9600);
+		cfsetospeed(&newtio, B9600);
+	break;
+	case 115200:
+		cfsetispeed(&newtio, B115200);
+		cfsetospeed(&newtio, B115200);
+	break;
+	default:
+		cfsetispeed(&newtio, B9600);
+		cfsetospeed(&newtio, B9600);
+	break;
+	}
+	
+	if( nStop == 1 )
+		newtio.c_cflag &= ~CSTOPB;
+	else if ( nStop == 2 )
+		newtio.c_cflag |= CSTOPB;
+	
+	newtio.c_cc[VMIN]  = 1;  /* 读数据时的最小字节数: 没读到这些数据我就不返回! */
+	newtio.c_cc[VTIME] = 0; /* 等待第1个数据的时间: 
+	                         * 比如VMIN设为10表示至少读到10个数据才返回,
+	                         * 但是没有数据总不能一直等吧? 可以设置VTIME(单位是10秒)
+	                         * 假设VTIME=1，表示: 
+	                         *    10秒内一个数据都没有的话就返回
+	                         *    如果10秒内至少读到了1个字节，那就继续等待，完全读到VMIN个数据再返回
+	                         */
+
+	tcflush(fd,TCIFLUSH);
+	
+	if((tcsetattr(fd,TCSANOW,&newtio))!=0)
+	{
+		perror("com set error");
+		return -1;
+	}
+	//printf("set done!\n");
+	return 0;
+}
+
+int open_port(char *com)
+{
+	int fd;
+	//fd = open(com, O_RDWR|O_NOCTTY|O_NDELAY);
+	fd = open(com, O_RDWR|O_NOCTTY);
+    if (-1 == fd){
+		return(-1);
+    }
+	
+	  if(fcntl(fd, F_SETFL, 0)<0) /* 设置串口为阻塞状态*/
+	  {
+			printf("fcntl failed!\n");
+			return -1;
+	  }
+  
+	  return fd;
+}
+
+
+/*
+ * ./serial_send_recv <dev>
+ */
+int main(int argc, char **argv)
+{
+	int fd;
+	int iRet;
+	char c;
+
+	/* 1. open */
+
+	/* 2. setup 
+	 * 115200,8N1
+	 * RAW mode
+	 * return data immediately
+	 */
+
+	/* 3. write and read */
+	
+	if (argc != 2)
+	{
+		printf("Usage: \n");
+		printf("%s </dev/ttySAC1 or other>\n", argv[0]);
+		return -1;
+	}
+
+	fd = open_port(argv[1]);
+	if (fd < 0)
+	{
+		printf("open %s err!\n", argv[1]);
+		return -1;
+	}
+
+	iRet = set_opt(fd, 115200, 8, 'N', 1);
+	if (iRet)
+	{
+		printf("set port err!\n");
+		return -1;
+	}
+
+	printf("Enter a char: ");
+	while (1)
+	{
+		scanf("%c", &c);
+		iRet = write(fd, &c, 1);
+		iRet = read(fd, &c, 1);
+		if (iRet == 1)
+			printf("get: %02x %c\n", c, c);
+		else
+			printf("can not get data\n");
+	}
+
+	return 0;
+}
+
diff --git a/IMX6ULL/source/09_UART/02_gps/gps_read.c b/IMX6ULL/source/09_UART/02_gps/gps_read.c
new file mode 100644
index 0000000..684f6ec
--- /dev/null
+++ b/IMX6ULL/source/09_UART/02_gps/gps_read.c
@@ -0,0 +1,257 @@
+#include <stdio.h>
+#include <string.h>
+#include <sys/types.h>
+#include <errno.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <termios.h>
+#include <stdlib.h>
+
+/* set_opt(fd,115200,8,'N',1) */
+int set_opt(int fd,int nSpeed, int nBits, char nEvent, int nStop)
+{
+	struct termios newtio,oldtio;
+	
+	if ( tcgetattr( fd,&oldtio) != 0) { 
+		perror("SetupSerial 1");
+		return -1;
+	}
+	
+	bzero( &newtio, sizeof( newtio ) );
+	newtio.c_cflag |= CLOCAL | CREAD; 
+	newtio.c_cflag &= ~CSIZE; 
+
+	newtio.c_lflag  &= ~(ICANON | ECHO | ECHOE | ISIG);  /*Input*/
+	newtio.c_oflag  &= ~OPOST;   /*Output*/
+
+	switch( nBits )
+	{
+	case 7:
+		newtio.c_cflag |= CS7;
+	break;
+	case 8:
+		newtio.c_cflag |= CS8;
+	break;
+	}
+
+	switch( nEvent )
+	{
+	case 'O':
+		newtio.c_cflag |= PARENB;
+		newtio.c_cflag |= PARODD;
+		newtio.c_iflag |= (INPCK | ISTRIP);
+	break;
+	case 'E': 
+		newtio.c_iflag |= (INPCK | ISTRIP);
+		newtio.c_cflag |= PARENB;
+		newtio.c_cflag &= ~PARODD;
+	break;
+	case 'N': 
+		newtio.c_cflag &= ~PARENB;
+	break;
+	}
+
+	switch( nSpeed )
+	{
+	case 2400:
+		cfsetispeed(&newtio, B2400);
+		cfsetospeed(&newtio, B2400);
+	break;
+	case 4800:
+		cfsetispeed(&newtio, B4800);
+		cfsetospeed(&newtio, B4800);
+	break;
+	case 9600:
+		cfsetispeed(&newtio, B9600);
+		cfsetospeed(&newtio, B9600);
+	break;
+	case 115200:
+		cfsetispeed(&newtio, B115200);
+		cfsetospeed(&newtio, B115200);
+	break;
+	default:
+		cfsetispeed(&newtio, B9600);
+		cfsetospeed(&newtio, B9600);
+	break;
+	}
+	
+	if( nStop == 1 )
+		newtio.c_cflag &= ~CSTOPB;
+	else if ( nStop == 2 )
+		newtio.c_cflag |= CSTOPB;
+	
+	newtio.c_cc[VMIN]  = 1;  /* 读数据时的最小字节数: 没读到这些数据我就不返回! */
+	newtio.c_cc[VTIME] = 0; /* 等待第1个数据的时间: 
+	                         * 比如VMIN设为10表示至少读到10个数据才返回,
+	                         * 但是没有数据总不能一直等吧? 可以设置VTIME(单位是10秒)
+	                         * 假设VTIME=1，表示: 
+	                         *    10秒内一个数据都没有的话就返回
+	                         *    如果10秒内至少读到了1个字节，那就继续等待，完全读到VMIN个数据再返回
+	                         */
+
+	tcflush(fd,TCIFLUSH);
+	
+	if((tcsetattr(fd,TCSANOW,&newtio))!=0)
+	{
+		perror("com set error");
+		return -1;
+	}
+	//printf("set done!\n");
+	return 0;
+}
+
+int open_port(char *com)
+{
+	int fd;
+	//fd = open(com, O_RDWR|O_NOCTTY|O_NDELAY);
+	fd = open(com, O_RDWR|O_NOCTTY);
+    if (-1 == fd){
+		return(-1);
+    }
+	
+	  if(fcntl(fd, F_SETFL, 0)<0) /* 设置串口为阻塞状态*/
+	  {
+			printf("fcntl failed!\n");
+			return -1;
+	  }
+  
+	  return fd;
+}
+
+
+int read_gps_raw_data(int fd, char *buf)
+{
+	int i = 0;
+	int iRet;
+	char c;
+	int start = 0;
+	
+	while (1)
+	{
+		iRet = read(fd, &c, 1);
+		if (iRet == 1)
+		{
+			if (c == '$')
+				start = 1;
+			if (start)
+			{
+				buf[i++] = c;
+			}
+			if (c == '\n' || c == '\r')
+				return 0;
+		}
+		else
+		{
+			return -1;
+		}
+	}
+}
+
+/* eg. $GPGGA,082559.00,4005.22599,N,11632.58234,E,1,04,3.08,14.6,M,-5.6,M,,*76"<CR><LF> */
+int parse_gps_raw_data(char *buf, char *time, char *lat, char *ns, char *lng, char *ew)
+{
+	char tmp[10];
+	
+	if (buf[0] != '$')
+		return -1;
+	else if (strncmp(buf+3, "GGA", 3) != 0)
+		return -1;
+	else if (strstr(buf, ",,,,,"))
+	{
+		printf("Place the GPS to open area\n");
+		return -1;
+	}
+	else {
+		//printf("raw data: %s\n", buf);
+		sscanf(buf, "%[^,],%[^,],%[^,],%[^,],%[^,],%[^,]", tmp, time, lat, ns, lng, ew);
+		return 0;
+	}
+}
+
+
+/*
+ * ./serial_send_recv <dev>
+ */
+int main(int argc, char **argv)
+{
+	int fd;
+	int iRet;
+	char c;
+	char buf[1000];
+	char time[100];
+	char Lat[100]; 
+	char ns[100]; 
+	char Lng[100]; 
+	char ew[100];
+
+	float fLat, fLng;
+
+	/* 1. open */
+
+	/* 2. setup 
+	 * 115200,8N1
+	 * RAW mode
+	 * return data immediately
+	 */
+
+	/* 3. write and read */
+	
+	if (argc != 2)
+	{
+		printf("Usage: \n");
+		printf("%s </dev/ttySAC1 or other>\n", argv[0]);
+		return -1;
+	}
+
+	fd = open_port(argv[1]);
+	if (fd < 0)
+	{
+		printf("open %s err!\n", argv[1]);
+		return -1;
+	}
+
+	iRet = set_opt(fd, 9600, 8, 'N', 1);
+	if (iRet)
+	{
+		printf("set port err!\n");
+		return -1;
+	}
+
+	while (1)
+	{
+		/* eg. $GPGGA,082559.00,4005.22599,N,11632.58234,E,1,04,3.08,14.6,M,-5.6,M,,*76"<CR><LF>*/
+		/* read line */
+		iRet = read_gps_raw_data(fd, buf);
+		
+		/* parse line */
+		if (iRet == 0)
+		{
+			iRet = parse_gps_raw_data(buf, time, Lat, ns, Lng, ew);
+		}
+		
+		/* printf */
+		if (iRet == 0)
+		{
+			printf("Time : %s\n", time);
+			printf("ns   : %s\n", ns);
+			printf("ew   : %s\n", ew);
+			printf("Lat  : %s\n", Lat);
+			printf("Lng  : %s\n", Lng);
+
+			/* 纬度格式: ddmm.mmmm */
+			sscanf(Lat+2, "%f", &fLat);
+			fLat = fLat / 60;
+			fLat += (Lat[0] - '0')*10 + (Lat[1] - '0');
+
+			/* 经度格式: dddmm.mmmm */
+			sscanf(Lng+3, "%f", &fLng);
+			fLng = fLng / 60;
+			fLng += (Lng[0] - '0')*100 + (Lng[1] - '0')*10 + (Lng[2] - '0');
+			printf("Lng,Lat: %.06f,%.06f\n", fLng, fLat);
+		}
+	}
+
+	return 0;
+}
+
diff --git a/README.md b/README.md
index deed72a..0f9eea8 100644
--- a/README.md
+++ b/README.md
@@ -326,6 +326,13 @@ git clone https://e.coding.net/weidongshan/linux/doc_and_source_for_drivers.git
   04_TTY驱动程序框架
   ```
 
+* 2021.07.19 发布"UART子系统"
+
+  ```shell
+  5a_在STM32MP157上做串口实验的准备工作
+  05_Linux串口应用编程_回环
+  06_Linux串口应用编程_GPS
+  ```
 
 ## 6. 联系方式
 
diff --git a/STM32MP157/doc_pic/09_UART/04_a_先修改STM32MP157的设备树以使用UART8.md b/STM32MP157/doc_pic/09_UART/04_a_先修改STM32MP157的设备树以使用UART8.md
deleted file mode 100644
index f9dde2e..0000000
--- a/STM32MP157/doc_pic/09_UART/04_a_先修改STM32MP157的设备树以使用UART8.md
+++ /dev/null
@@ -1,63 +0,0 @@
-## 先修改STM32MP157的设备树以使用UART8
-
-
-
-### 1. 只关注APP开发的话
-
-把GIT仓库中这个dtb文件复制到开发板上去就可以：
-
-```shell
-doc_and_source_for_drivers\STM32MP157\source\A7\09_UART\00_stm32mp157_devicetree_for_uart8\dtb
-	stm32mp157c-100ask-512d-lcd-v1.dtb
-```
-
-
-
-操作方法：
-
-  * Ubuntu上：复制dtb文件到NFS目录：
-
-    ```shell
-    $ cp stm32mp157c-100ask-512d-lcd-v1.dtb ~/nfs_rootfs/
-    ```
-
-  * 开发板上挂载NFS文件系统
-
-    * vmware使用NAT(假设windowsIP为192.168.1.100)
-
-      ```shell
-      [root@100ask:~]# mount -t nfs -o nolock,vers=3,port=2049,mountport=9999 
-      192.168.1.100:/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192.168.1.137
-
-      ```shell
-      [root@100ask:~]#  mount -t nfs -o nolock,vers=3 192.168.1.137:/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
-
-* 在串口可以看到以下设备节点
-
-  ```shell
-  ls  /dev/ttySTM*
-  /dev/ttySTM0
-  /dev/ttySTM1
-  /dev/ttySTM3
-  ```
-
-  
-
-
-
-### 2. 从头修改设备树文件
-
diff --git a/STM32MP157/doc_pic/09_UART/05_Linux串口应用编程.md b/STM32MP157/doc_pic/09_UART/05_Linux串口应用编程.md
index e215879..313630b 100644
--- a/STM32MP157/doc_pic/09_UART/05_Linux串口应用编程.md
+++ b/STM32MP157/doc_pic/09_UART/05_Linux串口应用编程.md
@@ -97,7 +97,15 @@ export PATH=$PATH:/home/book/100ask_imx6ull-sdk/ToolChain/arm-buildroot-linux-gn
 
 
 
-编译、执行程序
+编译、执行程序:
+
+```shell
+1. Ubuntu上
+arm-buildroot-linux-gnueabihf-gcc -o serial_send_recv serial_send_recv.c
+
+2. 板子上
+/mnt/serial_send_recv  /dev/ttymxc5
+```
 
 
 
@@ -113,7 +121,17 @@ export PATH=$PATH:/home/book/100ask_stm32mp157_pro-sdk/ToolChain/arm-buildroot-l
 
 
 
-编译、执行程序
+编译、执行程序:
+
+```shell
+1. Ubuntu上
+arm-buildroot-linux-gnueabihf-gcc -o serial_send_recv serial_send_recv.c
+
+2. 板子上
+/mnt/serial_send_recv  /dev/ttySTM3
+```
+
+
 
 
 
@@ -211,7 +229,17 @@ export PATH=$PATH:/home/book/100ask_imx6ull-sdk/ToolChain/arm-buildroot-linux-gn
 
 
 
-编译、执行程序
+编译、执行程序:
+
+```shell
+1. Ubuntu上
+arm-buildroot-linux-gnueabihf-gcc -o gps_read gps_read.c
+
+2. 板子上
+/mnt/gps_read  /dev/ttymxc5
+```
+
+
 
 
 
@@ -227,7 +255,17 @@ export PATH=$PATH:/home/book/100ask_stm32mp157_pro-sdk/ToolChain/arm-buildroot-l
 
 
 
-编译、执行程序
+编译、执行程序：
+
+```shell
+1. Ubuntu上
+arm-buildroot-linux-gnueabihf-gcc -o gps_read gps_read.c
+
+2. 板子上
+/mnt/gps_read  /dev/ttySTM3
+```
+
+
 
 
 
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diff --git a/STM32MP157/doc_pic/09_UART/05_a_在STM32MP157上做串口实验的准备工作.md b/STM32MP157/doc_pic/09_UART/05_a_在STM32MP157上做串口实验的准备工作.md
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@@ -0,0 +1,196 @@
+## 在STM32MP157上做串口实验的准备工作
+
+* 本节课程源码在GIT仓库里
+  ```shell
+doc_and_source_for_drivers\STM32MP157\source\A7\09_UART
+	    00_stm32mp157_devicetree_for_uart8
+	```
+
+
+
+### 1. 出厂系统不支持扩展板上的UART
+
+![](../../../IMX6ULL/doc_pic/09_UART/pic/09_UART/18_gps_to_stm32mp157.png)
+
+
+
+### 2. 只关注APP开发的话
+
+把GIT仓库中这个dtb文件复制到开发板上去就可以：
+
+```shell
+doc_and_source_for_drivers\STM32MP157\source\A7\09_UART\00_stm32mp157_devicetree_for_uart8\dtb
+	stm32mp157c-100ask-512d-lcd-v1.dtb
+```
+
+
+
+操作方法：
+
+  * Ubuntu上：复制dtb文件到NFS目录：
+
+    ```shell
+    $ cp stm32mp157c-100ask-512d-lcd-v1.dtb ~/nfs_rootfs/
+    ```
+
+  * 开发板上挂载NFS文件系统
+
+    * vmware使用NAT(假设windowsIP为193.168.1.100)
+
+      ```shell
+      [root@100ask:~]# mount -t nfs -o nolock,vers=3,port=2049,mountport=9999 
+      193.168.1.100:/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193.168.1.137
+
+      ```shell
+      [root@100ask:~]#  mount -t nfs -o nolock,vers=3 193.168.1.137:/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
+
+* 在串口可以看到以下设备节点
+
+  ```shell
+  ls  /dev/ttySTM*
+  /dev/ttySTM0
+  /dev/ttySTM1
+  /dev/ttySTM3
+  ```
+
+  
+
+
+
+### 3. 从头修改设备树文件
+
+#### 3.1 确定硬件资源
+
+观察STM32MP157的扩展板，背后写着: UART8_TX, UART8_RX，如下图：
+
+![image-20210719092503508](../../../IMX6ULL/doc_pic/09_UART/pic/09_UART/19_stm32mp157_extend_board_back.png)
+
+
+
+打开STM32MP157底板原理图，可知UART8_TX、UART8_RX使用引脚PE1、PE0，如下图：
+
+![image-20210719092726986](../../../IMX6ULL/doc_pic/09_UART/pic/09_UART/20_stm32mp157_pins_of_uart8.png)
+
+
+
+#### 3.2 使能设备树节点
+
+在STM32MP157的内核设备树文件`arch/arm/boot/dts/stm32mp151.dtsi`中，已经设置了uart8节点：
+
+![image-20210719092138173](C:/Users/weidongshan/AppData/Roaming/Typora/typora-user-images/image-20210719092138173.png)
+
+我们需要使能这个节点，往下看。
+
+#### 3.3 通过Pinctrl指定引脚
+
+光使能UART8还不行，还需要为它选择引脚。
+
+修改`arch/arm/boot/dts/stm32mp15xx-100ask.dtsi`，如下：
+
+```shell
+&uart8 {
+        pinctrl-names = "default", "sleep";
+        pinctrl-0 = <&uart8_pins_mx>;
+        pinctrl-1 = <&uart8_sleep_pins_mx>;
+        status = "okay";
+};
+```
+
+
+
+这些Pinctrl信息已经在`arm/boot/dts/stm32mp157-100ask-pinctrl.dtsi`中有了，无需我们添加：
+
+![image-20210719092949939](../../../IMX6ULL/doc_pic/09_UART/pic/09_UART/21_stm32mp157_uart8_pinctrl.png)
+
+
+
+#### 3.4 指定设备别名
+
+UART8对应的设备节点是哪个？它的驱动程序需要从"别名"里确定编号。
+
+修改`arch/arm/boot/dts/stm32mp157c-100ask-512d-v1.dts`，如下：
+
+```shell
+	aliases {
+		ethernet0 = &ethernet0;
+		serial0 = &uart4; //debug
+		serial1 = &usart6; //rs485
+		serial2 = &usart1; //bluetooth
+		serial3 = &uart8;  // extend board uart, /dev/ttySTM3
+	};
+```
+
+
+
+#### 3.5 编译、使用
+
+  * 设置工具链
+
+  ```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
+  ```
+
+  * 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-v1.dtb`
+
+    ```shell
+    make dtbs
+    ```
+
+  * 复制到NFS目录：
+
+    ```shell
+    $ cp arch/arm/boot/dts/stm32mp157c-100ask-512d-lcd-v1.dtb ~/nfs_rootfs/
+    ```
+
+  * 开发板上挂载NFS文件系统
+
+    * vmware使用NAT(假设windowsIP为193.168.1.100)
+
+      ```shell
+      [root@100ask:~]# mount -t nfs -o nolock,vers=3,port=2049,mountport=9999 
+      193.168.1.100:/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193.168.1.137
+
+      ```shell
+      [root@100ask:~]#  mount -t nfs -o nolock,vers=3 193.168.1.137:/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
+
+* 在串口可以看到以下设备节点
+
+  ```shell
+  ls  /dev/ttySTM*
+  /dev/ttySTM0
+  /dev/ttySTM1
+  /dev/ttySTM3
+  ```
+
diff --git a/STM32MP157/doc_pic/09_UART/pic/09_UART/19_stm32mp157_extend_board_back.png b/STM32MP157/doc_pic/09_UART/pic/09_UART/19_stm32mp157_extend_board_back.png
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