Max Kotasek <mawr...@gmail.com> writes:
> Hello to all out there,
>
> I'm trying to figure out how to parse the responses from fcntl.ioctl()
> calls that modify the serial lines in a way that asserts that the line
> is now changed. For example I may want to drop RTS explicitly, and
> assert that the line has been dropped before returning.
>
> Here is a brief snippet of code that I've been using to do that, but
> not sure what to do with the returned response:
>
> def set_RTS(self, state=True):
> if self.fd is None:
> return 0
>
> p = struct.pack('I', termios.TIOCM_RTS)
> if state:
> return fcntl.ioctl(self.fd, termios.TIOCMBIS, p)
> else:
> return fcntl.ioctl(self.fd, termios.TIOCMBIC, p)
>
> The problem is I get responses like '\x01\x00\x00\x00', or
> '\x02\x00\x00\x00' and I'm not sure what they mean.
I'm not an expert in this by any means. However, I don't think that
fcntl call actually returns the port status after the bit setting. But
why not check it explicitly with termios.TIOCMGET? At least then I
seem to be able to toggle the RTS bit (bit 2) in the register. Here
are the trivial functions I used:
def set_rts(fd):
print "Setting RTS."
p = struct.pack('I', termios.TIOCM_RTS)
fcntl.ioctl(fd, termios.TIOCMBIS, p)
def clear_rts(fd):
print "Clearing RTS."
p = struct.pack('I', termios.TIOCM_RTS)
fcntl.ioctl(fd, termios.TIOCMBIC, p)
def get_status(fd):
print "Querying RTS state."
stat = struct.pack('I', 0)
rc = fcntl.ioctl(fd, termios.TIOCMGET, stat)
if struct.unpack('I', rc)[0] & termios.TIOCM_RTS:
print "RTS bit is on."
else:
print "RTS bit is off."
It seems to me also that RTS is always on after the port has been
opened. I didn't dig out my voltmeter or anything to check this,
though.
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