1. Introduction

In previous articles, we developed applications that were embedded into the kernel within initramfs. Each time we needed to change the application, recompiling the kernel was cumbersome. Now, we will port lrzsz to enable file import and export via the serial port, making it easier to update applications by importing them into the RAM file system through the serial port, although this will not persist after power loss. In the future, we can add FLASH drivers to mount the FLASH file system and store programs in FLASH.

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2. Process

lrzsz is an open-source x/y/z modem implementation under Unix, see https://ohse.de/uwe/software/lrzsz.html.

We enter the working directory

cd ~/linux/src

Download the source code

wget https://ohse.de/uwe/releases/lrzsz-0.12.20.tar.gz

Extract the source code

tar -xvf lrzsz-0.12.20.tar.gzcd lrzsz-0.12.20/

Configure

CFLAGS="-Os -static" CC=arm-buildroot-uclinux-uclibcgnueabi-gcc ./configure

Compile

make

An error occurred

error.c:(.text+0x0): multiple definition of `error'

Modify error.c

Add conditional compilation

#if HAVE_STRERROR==0#endif

The compiled programs are located in src as lrz, lsz

qinyunti@qinyunti:~/linux/src/lrzsz-0.12.20$ ls src/lrz -al-rwxr--r-- 1 qinyunti qinyunti 116048 May 20 22:30 src/lrzqinyunti@qinyunti:~/linux/src/lrzsz-0.12.20$ ls src/lsz -al-rwxr--r-- 1 qinyunti qinyunti 115896 May 20 22:30 src/lszqinyunti@qinyunti:~/linux/src/lrzsz-0.12.20$

According to the previous article, add lrz to initramfs. Rebuild the kernel and flash it.

3. Testing

Due to space limitations, we only included lrz in the kernel.

So we first use lrz to import lsz

chmod +x ~/linux/src/lrzsz-0.12.20/src/lszcp ~/linux/src/lrzsz-0.12.20/src/lsz /mnt/d

Here, the host computer uses SecureCRT

In the shell, type lrz, a file selection dialog will pop up to select lsz

Import completed as shown below

Next, we test using lsz to export

chmod +x lsz./lsz bin/lrz

Export location as shown below

We can see that we can now import and export files using lrz, lsz. Since the internal FLASH is only 2M, we should embed as few things in the kernel as possible, only embedding lrz. The remaining RAM has over 4M.

So after booting, we can import files into the RAM file system using lrz.

Here, after using lsz, the terminal will hang; we will address this issue later.

4. Conclusion

We have successfully ported lrzsz and implemented file import and export functionality. With larger RAM, importing files into RAM is more convenient. In the future, we can test programs without modifying the kernel, making development and testing easier.