Hello, I have narrowed down the issue I'm about to describe to keyspan.c; a Digi Edgeport/1 with identical configuration works fine. I am configuring a Raspberry Pi running 4.19.66 (though keyspan.c hasn't changed since 2017) to talk to a real-live vt420. Configuring agetty with systemd worked easy enough, but I found that XON/XOFF wasn't working. stty -a shows ixon and ixoff as appropriate, but sending Ctrl-S (tested from multiple ways of sending) had no effect on output in bash, or scrolling output. (Emacs, though, recognized it as the start of a search, so I knew it was getting down the line.) After a great deal of head-scratching on this, I went to look at the kernel source and found that keyspan.c does not appear to be honoring XOFF. I also have a Digi Edgeport/1 on hand (which uses io_ti.c), and when I swapped to that, everything worked fine - Ctrl-S caused the expected pause. As far as I can tell, keyspan.c simply never implemented handling of XOFF, but you guys are the experts there. I twiddled many, many settings with stty but could not find anything that would make it honor xoff/Ctrl-S with the Keyspan. Even as a regular user that would use that trick to pause scrolling, it had no effect. Different TERM settings also had no effect. Output of stty -a: speed 19200 baud; rows 24; columns 80; line = 0; intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>; eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W; lnext = ^V; discard = ^O; min = 1; time = 0; -parenb -parodd -cmspar cs8 hupcl -cstopb cread clocal -crtscts -ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl ixon ixoff -iuclc -ixany -imaxbel -iutf8 opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0 isig icanon -iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt echoctl echoke -flusho -extproc Thanks, John
