On 2012-10-23, Matt Schulte <matts@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Fri, Oct 19, 2012 at 4:21 PM, Theodore Ts'o <tytso@xxxxxxx> wrote:
>> On Wed, Oct 17, 2012 at 03:24:06PM -0500, Matt Schulte wrote:
>>>
>>> What I would need to have happen is for a flag to be set that says
>>> "enable 9-bit mode transmit" or something. When set, the first byte
>>> of data of a given write will go out with mark parity, then the rest
>>> of the bytes will have space parity. The one byte with mark is the
>>> address byte.
>
>> Why not just have a userspace library routine which simply uses
>> tcgetattr/tcsetattr to toggle a bit (probably a new bit in c_cflag) in
>> struct termios, issue the single byte write, and then toggle the bit
>> back?
Can it be guaranteed that it's going to be fast enough at high
baud-rates to prevent any gap between the first byte and subsequent
bytes?
>> In Linux, system calls are fast, so using some extra ioctl's to toggle
>> the termios structure is probably the way to go. It's also much more
>> general since it doesn't presume a very specific protocol (i.e., your
>> magic multi-drop protocol).
>
> Also this isn't a magic protocol, it is a very old protocol that is
> apparently still in use today because I have several customers still
> asking for it.
It's been pretty much a standard in the microctroller world for a
_long_ time. I remember 9-bit HW support with special interrupt on
the "address" byte from almost 30 years ago: when I first worked with
the Intel 8051 in 1983, it had 9-bit support in it's UART (and we used
it).
I now work for a company that has manufactured PC serial boards for
25+ years, and we still get regular requests for that feature (and our
boards do support it -- though our Linux driver does not).
--
Grant Edwards grant.b.edwards Yow! I guess you guys got
at BIG MUSCLES from doing too
gmail.com much STUDYING!
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