Russell King wrote:
On Fri, Feb 17, 2006 at 05:25:29PM -0500, [email protected] wrote:
CRTSCTS CRTSHDX Handshaking
off off None. (Computer might as well send RTS< but ignores CTS)
on off Full-duplex RTS/CTS
off on RS-485. CTS ignored, RTS enables transmitter.
on on RS-232 half-duplex. RTS is request, CTS is grant.
...
Also, !CRTSCTS is most likely the state used by any existing userspace
RS485 implementations which would be using TIOCMBIC/TIOCMBIS to
manipulate the RTS signal, so having RTS manipulated in this state
would be an undesirable change of behaviour.
Hence, I'm very much in favour of having the default flow control
method to preserve in as many ways as possible existing behaviour
for CRTSCTS.
It is important to maintain the "driver doesn't touch RTS/CTS"
semantics without regard to other (new) control flags.
An application might read the existing termios, and modify only
the bits it is aware of without verifying that new bits are zero.
CFLOWXXX also maintains a free setting for future flow modes, such as:
CFLOWZEN = alter RTS based on /dev/random
--
Paul Fulghum
Microgate Systems, Ltd
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