How to read from a serial port in lua

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清歌不尽
清歌不尽 2021-01-18 03:40

I\'m new to lua and I\'m trying to receive data from the port, ttyACM0, I can write to the port by:

wserial = io.open(\"/dev/ttyACM0\",\"w\")
wserial:write(\         


        
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  • 2021-01-18 04:00

    I will not answer what you did wrong, but based one 1 answer here I did this for Windows environment:

    -- You can generate PowerShell script at run-time
    local script = [[
        $port= new-Object System.IO.Ports.SerialPort COM78,115200,None,8,one
        $port.open()
        $port.WriteLine('serialRequest')
        $port.ReadLine() > 'c:\\temp\\serialResponse.txt'
        $port.Close()
    ]]
    -- Now create powershell process and feed your script to its stdin
    local pipe = io.popen("powershell -command -", "w")
    pipe:write(script)
    pipe:close()
    

    Not very nice as response must be taken from file, but it works.

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  • 2021-01-18 04:14

    There are two kinds of line buffering going on here: one in the C library, which you can avoid using :read(1) like @Advert mentioned in the comments, and another one in the terminal driver itself. You can disable input line buffering in the terminal driver using the stty command line utility (stty -F /dev/ttyACM0 -icanon) or e.g. using luaposix (untested code):

    local p = require( "posix" )
    local rserial = assert( io.open( "/dev/ttyACM0", "r" ) )
    local fd = assert( p.fileno( rserial ) )
    
    local function table_copy( t )
      local copy = {}
      for k,v in pairs( t ) do
        if type( v ) == "table" then
          copy[ k ] = table_copy( v )
        else
          copy[ k ] = v
        end
      end
      return copy
    end
    
    -- get current settings
    local saved_tcattr = assert( p.tcgetattr( fd ) )
    local raw_tcattr = table_copy( saved_tcattr )
    -- clear ICANON bits from local flags using Lua 5.2 bit32 module
    raw_tcattr.lflag = bit32.band( raw_tcattr.lflag, bit32.bnot( p.ICANON ) )
    
    -- apply modified settings
    assert( p.tcsetattr( fd, p.TCSANOW, raw_tcattr ) )
    local c = rserial:read( 1 )
    print( c )
    -- restore default settings afterwards
    p.tcsetattr( fd, p.TCSANOW, saved_tcattr )
    rserial:close()
    

    There is also a specialized C module for handling serial ports in Lua, and the latest unreleased version of LuaSocket has code for handling serial ports (but it's disabled in default builds).

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