Openwrt (VIII) application layer development

One 、 The application and kernel layer

Many people begin to learn embedded system only after learning MCU Linux Of , At the beginning, I couldn't understand why writing two programs can light up LED, In the past, a single-chip computer only needed to write a program to go in LED You can control it ？ This is the idea of layering brought about by the operating system . In fact, we can also directly control in the drive , But this loses the meaning of the operating system .

The driver is in the kernel layer , The application is in the application layer . Relationship between them ：

application ——》 drive （ Call the driver to operate the underlying hardware ）

Two 、 Application instance

Examples can best explain knowledge , Our application program calls the character driver in the previous section . The following content can be used as a template in the future .

1、 stay package Create a new folder chardrv_app Folder

2、 stay chardrv_app Create a new folder Makefile file , The contents are as follows ：

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        #
        
# Copyright (C) 2009-2010 Jo-Philipp Wich <[email protected]>
        
#
        
# This is free software, licensed under the GNU General Public License v2.
        
# See /LICENSE for more information.
        
#
        

        
include $(TOPDIR)/rules.mk
        

        
PKG_NAME:=chardrv_app
        
PKG_RELEASE:=9
        

        
PKG_BUILD_DIR := $(BUILD_DIR)/$(PKG_NAME)
        

        
include $(INCLUDE_DIR)/package.mk
        

        
define Package/chardrv_app
        
  SECTION:=utils
        
  CATEGORY:=Utilities
        
  TITLE:=CharDrv_app
        
  DEPENDS:=+libncurses
        
endef
        

        
define Package/chardrv_app/description
        
 This package contains an character driver.
        
endef
        

        
define Build/Prepare
        
    mkdir -p $(PKG_BUILD_DIR)
        
    $(CP) ./src/* $(PKG_BUILD_DIR)/
        
endef
        

        
define Build/Configure
        
endef
        

        
define Build/Compile
        
    $(MAKE) -C $(PKG_BUILD_DIR) \
        
        CC="$(TARGET_CC)" \
        
        CFLAGS="$(TARGET_CFLAGS) -Wall" \
        
        LDFLAGS="$(TARGET_LDFLAGS)"
        
endef
        

        
define Package/chardrv_app/install
        
    $(INSTALL_DIR) $(1)/usr/sbin
        
    $(INSTALL_BIN) $(PKG_BUILD_DIR)/chardrv_app $(1)/usr/sbin/
        
endef
        

        
$(eval $(call BuildPackage,chardrv_app))
       
       

        
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above Makefile And driven Makefile Basically similar , It can be downloaded from package For other modules Makefile To make changes , I use the above nvram Of Makefile To modify .

3、 stay chardrv_app Create a new folder src Folder , stay src So let's make a new one Makefile file , The content is ：

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        all: chardrv_app
        
OBJS = chardrv_app.o
        

        
CC = gcc
        
CCFLAGS = -Wall -c -o
        

        
%.o: %.c
        
    $(CC) $(CCFLAGS) [email protected] $< $(LDFLAGS)
        

        
chardrv_app: $(OBJS)
        
    $(CC) -o [email protected] $(OBJS) $(LDFLAGS)
        

        
clean:
        
    rm -f rbcfg *.o
       
       

        
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4、 stay src Under the new chardrv_app.c file . The contents are as follows ：

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        #include <stdio.h>
        
#include <string.h>
        
#include <fcntl.h>
        
#include <unistd.h>
        
#include <sys/types.h>
        
#include <sys/stat.h>
        
#include <sys/ioctl.h>
        

        
int main(int argc , char** argv)
        
{
        
    // device handle 
        
    int fd;
        
    int num = 1;
        

        
    // Open the driver module 
        
    fd = open("/dev/chardrv" , O_RDWR|O_NONBLOCK);
        
    if(fd < 0)
        
    {
        
        printf("can't open /dev/chardrv\n");
        
        return -1;
        
    }
        

        
    // Function test 
        
    write(fd,&num,1);
        
    read(fd,&num,1);
        
    ioctl(fd,1,1);
        
    close(fd);
        

        
    return 0;
        
}
       
       

        
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5、make menuconfig Select module

6、 Execute the following statements in turn to compile

make package/chardrv_app/compile V=99

make package/chardrv_app/install V=99

make package/index V=99

The compiled file is in openwrt/bin/ramips/packages/base/ Next , file name

chardrv_app_9_ramips_24kec.ipk

7、 Put the compiled firmware on the development board , Then test according to the following picture .

3、 ... and 、 Problems and solutions

​ The following problems occurred while installing the app ：​

​ resolvent ：​ Reuse make V=99 compile openwrt The firmware , Then download to the development board . The above problem is that the firmware is the previous one , It's not the latest . The drivers and applications should be compiled before the routing firmware is recompiled , Otherwise, there will be this problem .

​* When compiling, if the permission is insufficient , To add sudo, So you can compile and pass .​