Re: [patch] DTR/DSR hardware handshake support for 2.0/2.2/2.4

From: David Lawyer (
Date: Wed Aug 02 2000 - 14:56:34 EST

> Martin Schenk wrote:
> > DTR/DSR is a very often used handshake for serial printers, at least
> > in the POS field. A lot of supermarket cash registers are in fact PCs
> > with special hardware, which for some unclear reason typically knows
> > only about DTR/DSR handshaking (even if it is from other vendors:
> > SNI or EPSON does not make a difference: only DTR/DSR).

Text-terminals have been using DTR/DSR flow control for decades and
it's pretty much standard for them. POS terminals would be expected
to use the same flow control.

On Wed, Aug 02, 2000 at 11:47:28AM -0400, Frank da Cruz wrote:
> Yes, I'll second this. [Putting the DTR/DSR patch in the driver] I
I'll vote for it too.
> get requests for DTR/DSR (and DTR/CD) hardware flow control in
> Kermit all the time for this kind of reason. The equipment involved
> is not "legacy" (my least favorite word -- in common parlance it
> means "not Microsoft") at all, just weird.
> There are standard APIs in SVR4 for all sorts of hardware flow control,
> specified in <termiox.h> (or <sys/termiox.h>):
> ioctl(fd,command,arg)
> struct termiox * arg;
> The termiox struct contains a member:
> unsigned short x_hflag; /* hardware flow control modes */
> Which can be set to various combinations of:
> #define RTSXOFF 0000001 /* Enable RTS hwfc on input */
> #define CTSXON 0000002 /* Enable CTS hwfc on output */
> #define DTRXOFF 0000004 /* Enable DTR hwfc on input */
> #define CDXON 0000010 /* Enable CD hwfc on output */
> #define ISXOFF 0000020 /* Enable RTS hwfc on input */

Where is "DSR hwfc on output"? This is a serious omission since I
think it's more important than CD hwfc.

                        David Lawyer

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