Serial port crashes

steve64 · 2025-05-13T16:00:14+00:00

I'm observing total crashes when using the serial module. It's difficult to give you a full example since I got the problem when interacting with a special d...

Samir

Ok sorry I will still investigate

Samir

HI steve,

Here is a new version : [Login to see the link]

is it better now ?

steve64

very sorry, still crashing... thanks for your help
I think you should be close to the mistery now, but still something strange there...
Looks like a buffer issue in fact.. Lua is robust but the native code is "just C" 😉

Samir

Maybe you discovered a bug outside of the serial module.
Can you post me some code that reproduces the crash ?

steve64

you need an external device getting commands and generating replies, I'm using a specific device and any example would refer to that
I would suggest anyway to add some more checks on all usages of pointers inside the Port.c file.

Example:

PortTask *task = (PortTask *)calloc(1, sizeof(PortTask)); // no check for failure of calloc()

Samir

I don't think the crash will come from here...
Do you try to read() on the same Port at the same time ?

steve64

I'm not saying it comes exactly from that point, but all pointers in that file must be possibly checked to reduce the risk of crashes.
Now I'm trying to test by connecting another device, a RP 2040 Zero module over UART with a micro-Python on board,
Using TeraTerm or Thonny I can interact with its shell.
Trying to read and write with LuaRT serial module the Port.write() seems to work (returns a proper number of bytes written) but then a wait() after read() and readline() stucks forever (or sometimes crashes).

  reply = COM_PORT:write(cmd..'\r\n'):wait()
  print('write num', reply)
  repeat
    t = COM_PORT:read(1)
    print('--- after read ---', t, t.status) --> Task: 0000020F1E079950	sleeping
    local buf = t:wait() --> ALWAYS STUCKS HERE
  until not buf

steve64

A complete example (no UI):

local port_name = 'COM24'
local baudrate = 115200
local cmd, num, reply
    
local COM_PORT = serial.Port('\\\\.\\'..port_name)
if not COM_PORT then    
  print('serial port '..port_name..' not found')
  sys.exit(1)
end    
print('serial port '..port_name..' found')
  
if not COM_PORT:open({ baudrate=baudrate, bytesize=8 }) then
  print('serial port '..port_name..' not opened')
  sys.exit(1)
end  
print('serial port '..port_name..' opened')
  
cmd = 'x = 1234'
for i = 1 , 10 do
  num = COM_PORT:write(cmd..'\n'):wait()
  print(i, 'written:', num)
  COM_PORT:flush()
  buf = COM_PORT:readline('\r'):wait() --> WAIT FOREVER
  print(i, 'reply:', buf)
end
  
COM_PORT:close()
print('serial port '..port_name..' closed')

Samir

Thank U so much ! I will check this

steve64

A working Python example:

import serial
import time
serial_port = 'COM24'
baud_rate = 115200
try:
    ser = serial.Serial(serial_port, baud_rate, timeout=1)
    print(f"Connected to {serial_port} at {baud_rate} baud.")
    time.sleep(2)
    command = "help()\r\n"
    ser.write(command.encode('ascii'))
    print(f"Sent: {command.strip()}")
    while True:
        #response = ser.read_until('>>>').decode('ascii')
        response = ser.readline().decode('ascii')
        print(f'{response}', end='')
        if not response: break
    ser.close()
    print("\nSerial port closed")        
except serial.SerialException as e:
    print(f"Error: {e}")

Same example in LuaRT not working:

local serial = require 'serial'
  
local port_name = 'COM24'
local baudrate = 115200
local cmd, num, buf
    
local COM_PORT = serial.Port('\\\\.\\'..port_name)
if not COM_PORT then    
  print('serial port '..port_name..' not found')
  sys.exit(1)
end    
print('serial port '..port_name..' found')
  
if not COM_PORT:open({ baudrate=baudrate, bytesize=8 }) then
  print('serial port '..port_name..' not opened')
  sys.exit(1)
end  
print('serial port '..port_name..' opened')

sleep(2000)
cmd = sys.Buffer('help()\r\n')
num = COM_PORT:write(cmd):wait()
print('write, written:', num)
repeat
  t = COM_PORT:readline('\r\n')
  print(i, 't:', t, t.status)
  buf = t:wait() --> WAIT FOREVER
  print(buf)
until not buf
COM_PORT:close()
print('serial port '..port_name..' closed')

steve64

I discovered that the crashes seem to occur particular when the read() or readline() receive a quite long byte sequence from the serial port. Is there a limit on the buffer capacity (es. 256) inside Port.c?
I need to read back any sequence, let say at least 4KB in the worst case.
It would be also nice to allow a customization of the RX buffer size.

Samir

The buffer size adapts to the size provided by the argument of the read() method...

Maybe with large data the buffer might overflow...I will check this thank you

steve64

for read() the argument is the number of bytes to read, but for readline() how the destination buffer size is defined?

The buffer is reallocated until the \n character is received

steve64

any news?

Samir

Sorry I have a lot of work (on my real life work) and didn't have time to check this

steve64

yes, of course 😉 thanks for your help so far

Samir

It should be fixed :
[Login to see the link]

There was two other bugs, one with the write() method, and another one with readline()

Please tell me if it works as expected now

steve64

thanks a lot
from first tests it looks better, but I'm not totally sure yet, I will need further testing, will keep you updated

steve64

write() and read(1) now seem stable, I have a long term test that runs fine
I still see issues when using readline() but it's a minor aspect, I can survive with read() that is fast enough
thanks again

Samir

You're wekcome. For readline I had tested it with 92kb of lines without problem. Be sure the content ends with "\n"... If not it will wait indefintely

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