On 13/04/2017 17:12, Rodolfo Giometti wrote:
> On 04/13/17 16:53, Richard Genoud wrote:
>> 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.
>
> I see, but while PARMD defines a special parity usage the SENDA bit is
> dedicated to output data only... however if you prefer I use bits 23 and
> 24 it's OK for me! :-)
>
>> 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.
>
> This should be another reason because we should use c_oflag instead of
> c_cflag! :-P
Actually it isn't, I gave the example of c_cflag, but it's the same with
c_{i,o,l}flag
> Otherwise I really don't know how to manage the SENDA bit in a suitable
> way...
>
> Ciao,
>
> Rodolfo
>
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