Date: Fri, 17 Feb 2006 21:39:03 +0000
From: Russell King <rmk+lkml@arm.linux.org.uk>
To: Paul Fulghum <paulkf@microgate.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] SIIG 8-port serial boards support
Message-ID: <20060217213903.GE13502@flint.arm.linux.org.uk>
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	linux-kernel@vger.kernel.org
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On Fri, Feb 17, 2006 at 03:27:44PM -0600, Paul Fulghum wrote:
> Russell King wrote:
> >So, there are three distinct flow control scenarios:
> 
> So I'm clear on how you interpret these,
> am I correct with the following?
> 
> >- conventional RTS/CTS
> RTS active = ready to receive
> CTS active = allowed to send
> 
> >- alternative RTS/CTS
> RTS active = on before send, off after send
> CTS active = allowed to send

I'll have to dig through my archives to confirm this one.

> >- RS485
> RTS active = on before send, off after send (RTS enables driver)
> CTS ignored (2 wire mode, no CTS)
> 
> So maybe the extra control fields would be:
> CRTSONTX - RTS on before send, off after send
> CTXONCTS - wait for CTS before sending

That's a possibility, except that programs today expect CRTSCTS to
enable RTS/CTS flow control.

What I suggest is to use CRTSCTS to enable the chosen flow control
method.  Then we have a set of cflag bits which describe the flow
control mode, eg CFLOWRS485, CFLOWMODEM, CFLOWALT (probably needs
better names.)  CFLOWMODEM being the conventional mode should have
an all zeros value.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 Serial core
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