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Am 29.03.2013 12:04 schröbte Helen Fornazier:

Hello!


Hi!



I am new in Lua and I just start developing for OpenWRT in a Dragino
platform.

I want to develop an application that reads data from Uart and print it in
a Luci based web page.

But I am having a problem that I described here :
http://stackoverflow.com/questions/15701694/lua-io-read-sends-me-an-echo-back-when-i-read-from-serial-port-why

When I execute the code :

print("Dragino Uart Test started\n")while 1 do
     serialin=io.open("/dev/ttyS0","r")
     print(serialin:read())    --print the data
     serialin:close()end

I read the serial port but I receive an echo too and the read() waits
until a new line character to return.
Apart from the wrong call to read() which is already mentioned in lhf's stackoverflow answer, it seems you need to set some terminal attributes via tcsetattr[1]. Unfortunately neither nixio nor luaposix has support for this function. Typically you could execute the stty program to set those attributes from the commandline, but unfortunately busybox (at least on my openwrt) is compiled without support for stty. There is this module[2] and as Thijs already mentioned a version of luasocket which supports serial connections, but you would need to compile those yourself as well. 

  [1]: http://linux.die.net/man/3/tcsetattr
  [2]: http://lua-users.org/lists/lua-l/2011-10/msg00989.html



There is any other way to read from a serial port ?
If you don't want to touch a compiler I suggest the ser2net[3] daemon which can be installed via opkg. It handles mappings between terminal files and tcp sockets and forwards data between them. A quick glance at the source shows that it does "the right thing" in its terminal configuration, which is to disable echo and line buffering. You could then use the default nixio[4] (which comes bundled with luci) or luasocket modules to connect to the tcp port and read/write data ... 

  [3]: http://linux.die.net/man/8/ser2net
  [4]: http://luci.subsignal.org/api/nixio/index.html



Thank you for your help, I appreciate it.



HTH,
Philipp