On 13/04/2017 14:19, Rodolfo Giometti wrote:
> On 04/13/17 12:43, Richard Genoud wrote:
>> On 11/04/2017 22:12, Rodolfo Giometti wrote:
>>> 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.
>>>
>>> Signed-off-by: Rodolfo Giometti <giometti@xxxxxxxx>
>>> ---
>>> 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 83b264c..85238ff 100644
>>> --- a/include/linux/tty.h
>>> +++ b/include/linux/tty.h
>>> @@ -166,6 +166,8 @@ 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 232b478..7e82859 100644
>>> --- a/include/uapi/asm-generic/termbits.h
>>> +++ b/include/uapi/asm-generic/termbits.h
>>> @@ -140,6 +140,8 @@ struct ktermios {
>>> #define HUPCL 0002000
>>> #define CLOCAL 0004000
>>> #define CBAUDEX 0010000
>>> +#define PARMD 0100000
>>> +#define SENDA 0200000
>>> #define BOTHER 0010000
>>> #define B57600 0010001
>>> #define B115200 0010002
>>>
>> I guess there's a problem with SENDA (bit 16)
>> It's overlapping with CIBAUD (002003600000 (bits 28,19,18,17,16))
>
> You're right! In this case which bit should I use for SENDA? :(
>
> Since it is referred to output data maybe can we move it into c_oflag bits?
Well, bits 23 and 24 are free in asm-generic/c_cflag, and since
multidrop uses the parity bit, I'd say it fits better in c_cflag than in
c_oflag.
But honestly, I find the SENDA bit logic disturbing and not compliant
with the way tc{g,s}etattr() works.
Because, usually, a tcsetattr() call is followed by a tcgetattr() call
to check if everything went well. (tcsetattr return 0 if *any* of the
requested change succeeded).
So, with the proposed implementation, we will have
struct termios term, check;
ret = tcgetattr(fd, &term);
if (ret < 0) {
perror("tcgetattr");
exit(-1);
}
term.c_cflag |= PARENB | CMSPAR | PARMD | SENDA;
ret = tcsetattr(fd, TCSADRAIN, &term);
if (ret < 0) {
perror("tcsetattr");
exit(-1);
}
ret = tcgetattr(fd, &check);
if (term.c_cflag != check.c_cflag) {
/* fail to set all c_cflags */
exit(-1);
}
=> it will always fail.
Regards,
Richard.
--
To unsubscribe from this list: send the line "unsubscribe linux-serial" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
