I am writing a C program in Linux which will read/write to/from a serial port. I know the data that needs to be read and written on the port but I don't have a serial port to currently test this with.
Is there any way to simulate a serial port? Would reading/writing to a file be sufficient? I can have one process write to the file while another process reads that data and writes back other data to the file. Or are there others tools that can be used to simulate a port?
Thanks
Serial ports on Linux are terminal devices. A close simulation is to create a pseudo-terminal pair; the program that normally talks to the serial port is instead told to open the slave side of the pseudo-terminal, and the simulator writes and reads from the master side.
The pty(7) man page has more information.
Despite being an old topic, and my answer is not exactly something the OP was looking for, I decided to share my experience, as someone else might come across it like I did. Instead of straightforward simulation, I used the software called Serial to Ethernet Connector to gain access to the specific device I needed to test the app with. Worked nicely for me.
A character device, even something as simple as normal stdin and stdout should work if you don't care about attributes specific to port devices.
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I'm using a LPC178 development board and I want to read a file present on a Windows PC. My dev board only has a RS2323 interface to communicate with.
How can I go about transferring the file from my PC to my MCU using a RS232 (serial) link? I found a reference which explains how to transfer data between a MCU and PC but it isn't about file transfers.
Afaik there is no easy solution for this like calling something like "copy" or "fopen" over RS232. I would be happy to be proven wrong here.
The fastest solution might be to write a little programm running on your Windows Host, which listens to your RS232 communication and pipes your communication into/out of the file based on your communication protocol. This can be done with standard file operations in the language of your choice, for example C, C++ or Python.
Your problem is one of the oldest in the book. How do you transfer files without fancy operating system abstractions. For RS232 (or any other serial method) there exists many file transfer protocols.
One of them is kermit. This is a protocol from 1981 and can transfer binary and text files. It is able to be embedded in a micrcontroller and there exists programs to transfer/receive using kermit.
alternative old site for reference
In the simplest case you would use a file transfer protocol such as XMODEM, YMODEM, ZMODEM or Kermit - these protocols were designed in the days before networking and the Internet were ubiquitous and deal with simple point-to-point transfers between two computers. They are supported bu most terminal emulator tools such as TeraTerm Pro or PuTTY so no specific PC software need be written, just the microcontroller end.
A more complex but flexible solution is to implement a TCP/IP stack and a PPP driver, and an FTP application layer - probabaly only practical if using a third-party TCP/IP stack and application layer. You can then use any FTP client for the PC end, so again no PC software required. While this may be overkill if all you need to do is transfer files, it has the advantage of allowing you to use the the single serial port concurrently for other data streams and application protocols such as Telnet. The disadvantage perhaps is that while Windows does support PPP it is buried within the dial-up networking and to be frank a pain to get working.
Very first step you have to do is ensure serial communication is working fine.
Send a byte continuously from mcu to PC and display it on some io console (for example: HyperTerminal, Dock light )
Receive a byte to mcu from PC and echo it back to PC.
Once you are sure that serial communication is working fine then select some file transfer protocol and implement it.
While you can select any of the available protocols or write your own protocol and implement it.
For purpose of discussion i select Xmodem protocol.
If you consider some other protocol you may stop reading answer here.
XMODEM is a simple file transfer protocol.
Refer http://web.mit.edu/6.115/www/amulet/xmodem.htm for detailed information.
You may implement Xmodem mcu side by reading protocol. Or may consider using open source also ( if available )
PC side i prefer to use HyperTerminal io console as it is compatible with Xmodem.
In HyperTerminal all that i have to do is configure settings and select file for transfer to mcu.
Now transfer any file to mcu using Xmodem protocol from PC.
What you do with received file in mcu is up to you : )
I have a question linked to Linux and serial port.
I want to be able to receive and send messages to a dedicated serial port and to redirect it to another port (/dev/tty).
For the first part, I’m able to dialog with my hardware equipment without any problem, but I’m just wondering if it’s possible to intercept and redirect message coming from a serial port #1 to another port #2.
To give more context, I had used a GPS Antenna and NTP open source software for years.
Since 2018, the new GPS antenna protocol has modified the order of bytes in the message used by NTP to steer and now it’s not working anymore.
So my idea is to put a simple C program (middleware) which fixes this byte ordering; but I’m wondering if I have to build a kernel-specific module or if it can be done in another way. The NTP software uses the symbolic link to dialog.
Thanks for your help.
You can probably use a simple redirect, look here:
Pipe One Serial Port to Another in Linux
If the ports are in different rates you can use stty or perhaps screen to adjust: https://unix.stackexchange.com/a/117064
If you need it to be in c program to manipulate it you can use the following: https://stackoverflow.com/a/6947758/8901188
Using c it will need to run in an infinite loop so it can constantly read, manipulate and write the data.
I am trying to get a microcontroller to communicate with a Windows PC over serial port.
It looks to me like Windows is buffering the input on COM1 such that if I stop both programs running, then restart only the Windows program it is still receiving some output from the previous run of the microcontroller's program.
After I open COM1 can I some how flush its receive buffer before beginning to read? Is there a function call to do that?
I believe the function you are looking for is PurgeComm, to which you pass the HANDLE you got from CreateFile() when you opened the port. I'm not sure, but I believe the serial port is also automatically flushed each time you open it.
However, a better method is to use ReadFile (or ReadFileEx) until you encounter something meaningful. Serial protocols are always designed with one or more sync bytes for this very purpose. Unless you are writing a terminal program or similar, you will have to do like this anyhow, since the Windows PC will never be in sync with the microcontroller otherwise.
I just finished a small project written in C, where I read a data stream from a serial port and parse the incoming data.
The software is written for POSIX systems (using termios) and follows the standard steps to working with serial i/o
Opening the serial device using open()
Configuring communication parameters (termios)
Set blocking mode on file handle (fcntl)
Perform read() on serial interface.
Perform close() on serial interface when done.
Other than the socket parts, the code is straight ANSI C.
My question is, how involved would it be to make the code work on a windows platform.
The port would not be written by me, I'd only like to give an indication to others who might be interested in porting it (i.e. trivial, not so trivial, rip your eyes out insanity inducing).
Also if someone has Windows with "Windows Services for UNIX", would they be able to use the code without modifying it?
So, if anyone has experience with this could you please share.
It should be pretty easy to do. The names are very different, but the sequence of calls and concepts are very similar.
What you are looking for is the DCB structure which should be used with the SetComState() function to set baudrate, stopbits etc. Then use SetCommTimeouts() and set the timeout values in the COMMTIMEOUTS structure to make subsequent read calls blocking.
Here is a short introduction as a pretty PDF. (Backup.)
I am using C language and Linux as my programming platform. Right now I am learning some embedded programming. I am using a POS device for my practice session and my host is a Windows OS using a cygwin.
I created a simple application that will run in the target device that will read the data in the serial port and in the host side I created a simple application that will write the data in the serial port. Now my problem is when I am sending a data without 0x0a(LN) at the end of the buffer the target device will not receive that data. But I am not sure if that was sent or not. But when I put a 0x0a(LN) at the end of the buffer to send then the target device will receive that data.
Did I missed some configuration of my application? Or putting a 0x0a byte at the end of the tx buffer is the correct way.
Thanks
It sounds like your serial port (actually the 'terminal device' as far as Linux is concerned) may be in line-buffered mode. When setting it up with tcsetattr, be sure to clear c_lflag (you don't want ICANON). You should also check out the input/output flags that affect translation between CRLF and NL since you probably don't want that behavior either. Default terminal settings are oriented towards user/application interaction, not data transmission.
Sounds like it's doing line buffering. Do a flush after sending the data.