linux-kernel - RE: 9 bit serial / non-blocking TCSADRAIN

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Message-ID: <bb788810d84d491aa6357d411895242b@AcuMS.aculab.com>
Date:   Fri, 6 May 2022 10:59:22 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Baltazár Radics' <baltazar.radics@...il.com>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: 9 bit serial / non-blocking TCSADRAIN

From: Baltazár Radics
> Sent: 05 May 2022 18:02
> 
> I want to use a raspberry pi's serial to communicate over a protocol
> that uses 9-bit characters, so currently I'm using the stick parity
> mode (CMSPAR) and toggling between odd and even parity, then using
> tcsetattr with TCSADRAIN as the second argument, which blocks until all
> bytes are transmitted. Is there a non-blocking api to do the same
> thing, so I can use it from poll / select? (If there's a better way to
> do 9 bit character size, that'd be even better. For my protocol, the
> 9th bit is only used to tell address bytes from data bytes, so I don't
> have to change it often, so I guess my current method isn't too
> horrible.)

Does anything give the option of generating non-hdlc synchronous data?
You might be able to use two bytes to generate a single 9-bit
async character or three bytes to generate two 9-bit characters.

	David

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