Hi Rodolfo, You could also add these mailing lists: - linux-serial@xxxxxxxxxxxxxxx - linux-arm-kernel@xxxxxxxxxxxxxxxxxxx - linux-kernel@xxxxxxxxxxxxxxx For reference, I've dug the conversation we had 2 years ago: 0/2 : https://marc.info/?t=149192176100002&r=1&w=2 1/2 : https://marc.info/?t=149192176300001&r=1&w=2 2/2 : https://marc.info/?t=149192176700001&r=1&w=2 And, like I said at that time, one problem I see with this implementation (setting a SENDA bit that automatically unsets itself) will break the way tcgetattr() is working: https://marc.info/?l=linux-serial&m=149209522108027&w=2 Le 12/09/2019 à 10:40, Rodolfo Giometti a écrit : > From: Rodolfo Giometti <giometti@xxxxxxxx> > > Multidrop mode differentiates the data characters and the address > characters. Data is transmitted with the parity bit to 0 and addresses > are transmitted with the parity bit to 1. However this usually slow > down communication by adding a delay between the first byte and the > others. > > This patch defines two non-stadard bits PARMD (that enables multidrop) > and SENDA (that marks the next transmitted byte as address) that can > be used to completely remove the delay during transmission by > correctly managing the parity bit generation in hardware. > > A simple example code about how to set up it is reported below: > > struct termios term; > > tcgetattr(fd, &term); > > /* Transmission: enable parity multidrop and mark 1st byte as address */ > term.c_cflag |= PARENB | CMSPAR | PARMD | SENDA; > /* Reception: enable parity multidrop and parity check */ > term.c_iflag |= PARENB | PARMD | INPCK; > > tcsetattr(fd, TCSADRAIN, &term); > > After that we can start 9 bits data transmission. > > Signed-off-by: Rodolfo Giometti <giometti@xxxxxxxx> > Signed-off-by: Joshua Henderson <joshua.henderson@xxxxxxxxxxxxx> > --- > include/linux/tty.h | 2 ++ > include/uapi/asm-generic/termbits.h | 2 ++ > 2 files changed, 4 insertions(+) > > diff --git a/include/linux/tty.h b/include/linux/tty.h > index bfa4e2ee94a9..66a25294f125 100644 > --- a/include/linux/tty.h > +++ b/include/linux/tty.h > @@ -168,6 +168,8 @@ struct tty_bufhead { > #define C_CIBAUD(tty) _C_FLAG((tty), CIBAUD) > #define C_CRTSCTS(tty) _C_FLAG((tty), CRTSCTS) > #define C_CMSPAR(tty) _C_FLAG((tty), CMSPAR) > +#define C_PARMD(tty) _C_FLAG((tty), PARMD) > +#define C_SENDA(tty) _C_FLAG((tty), SENDA) > > #define L_ISIG(tty) _L_FLAG((tty), ISIG) > #define L_ICANON(tty) _L_FLAG((tty), ICANON) > diff --git a/include/uapi/asm-generic/termbits.h b/include/uapi/asm-generic/termbits.h > index 2fbaf9ae89dd..ead5eaebdd3b 100644 > --- a/include/uapi/asm-generic/termbits.h > +++ b/include/uapi/asm-generic/termbits.h > @@ -141,6 +141,8 @@ struct ktermios { > #define HUPCL 0002000 > #define CLOCAL 0004000 > #define CBAUDEX 0010000 > +#define PARMD 040000000 > +#define SENDA 0100000000 > #define BOTHER 0010000 > #define B57600 0010001 > #define B115200 0010002 >
