How to read from serial port in lua
I am new to lua and I am trying to get data from a port, ttyACM0, I can write to the port:
wserial = io.open("/dev/ttyACM0","w")
wserial:write("hellloooo")
wserial:flush()
I thought, since I can write in it the same way I would write to a file, which could read it the same way I would read a file. But when I try to read it (using the code below) I just end up in an infinite loop.
rserial=io.open("/dev/ttyACM0","r")
while chaine==nil do
chaine=rserial:read()
rserial:flush()
end
print(chaine)
So my question is, what am I doing wrong, how am I reading from the port, ttyACM0?
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There are two types of line buffering here, one in the C library, which you can avoid using :read(1)
like @Advert mentioned in the comments, and another in the terminal driver itself. You can turn off buffering of the input line in the terminal driver using the command line utility stty
( stty -F /dev/ttyACM0 -icanon
) or, for example, 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 is disabled in builds by default).
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