Using glib to send raw bytes to an FTDI device over USB

Question

I am developing a simple application in C with GTK+2.0 GUI, on Linux of course, this application is designed to control a device which is connected over the USB port and is using FTDI driver to emulate RS232 asynchronious protocol over the USB port.

I am using the function g_io_channel_write_chars() to send data to the device. The problem is the sequence I am sending consist a lot of values that are ASCII but do not match any (visible) character.

For example, when I am sending \x40\x40\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x01 it won't work. The program will stop with an error.

GLib:ERROR:/build/buildd/glib2.0-2.34.1/./glib/giochannel.c:2382:g_io_channel_write_chars: code should not be reached Przerwane (core dumped)

If I use sprintf function to put this sequence in a table only first two values will be copied and this sequence will be send to the device without an error.

Then my question is, how can I send any bytes to the device. Is there an equivalent of g_io_channel_write_chars() for this? I've been studying the documentation of GIOChannel and haven't found anything like this. Thanks very much for your help.

I don't know about g_io_channel_write_chars; but the "problem" with sprintf is that you can't use that function to copy correctly data containing \x00. Rather, use memcpy; what do you mean by "table"? depending on the answer, you could need no memcpy at all. — ShinTakezou
By table I meant "array", sorry this was a vocabulary error (I'm not a native english speaker). I've noticed that sprintf skips the \x00 and \x01 etc, this is why I created this array of those elements, tryied to send it but it crashes.. — Marek
sprintf is meant to be used with C-string. C-string are null terminated: it means the end of the string is recognized when a byte '\x00' is found, so you can't use it to handle properly data containing null bytes. You can copy the data in your array using memcpy(dest, "\x40\x40\x00...", 13) or similar — ShinTakezou
yes of course, unfortunately it does not solve the problem, which was sending raw data (the fact that g_io_channel_write_chars() crashes) — Marek

unwind unwind · Accepted Answer · 2013-05-22T10:17:53

You need to make sure the channel doesn't think it's sending text. The crash you're getting is probably due to GIO trying to validate your data against its idea of the channel's encoding.

Note that the default encoding is UTF-8, and since not all byte sequences are valid UTF-8, this can easily cause validation to fail for random binary data.

Call g_io_channel_set_encoding with the argument NULL, this will make it safe for binary data:

The encoding NULL is safe to use with binary data.

Using glib to send raw bytes to an FTDI device over USB

1 Answers