From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Stefan Agner <stefan@agner.ch>
Cc: linux-arm-kernel@lists.infradead.org, s.hauer@pengutronix.de,
baruch@tkos.co.il, linux-serial@vger.kernel.org
Subject: Re: serial: imx: half-duplex RS485 operation with RTS active low
Date: Mon, 16 Apr 2018 11:22:57 +0200 [thread overview]
Message-ID: <20180416092257.frbmooduhm4zrhhl@pengutronix.de> (raw)
In-Reply-To: <0e88706a05a302201be396d2f03c3e9e@agner.ch>
Hi Stefan,
On Mon, Apr 16, 2018 at 11:14:32AM +0200, Stefan Agner wrote:
> Using upstream I noticed that RS-485 does not work in the default
> configuration for our platforms (Toradex Apalis/Colibri). Closer
This is an i.MX6?
> debugging shows that it is related to "serial: imx: default to half
> duplex rs485".
>
> We use the i.MX UART in DTE mode and control the RS-485 transceiver
> using the RTS signal in low-active mode.
>
> uart-has-rtscts;
> fsl,dte-mode;
> linux,rs485-enabled-at-boot-time;
> rs485-rts-active-low;
That means you're not using a GPIO for RTS signaling, right?
> Using this setting leads to the RTS signal not getting asserted (the
> oscilloscope only shows a very short fluke before the start bit is
> sent).
>
> However, using
>
> uart-has-rtscts;
> fsl,dte-mode;
> linux,rs485-enabled-at-boot-time;
> rs485-rts-active-low;
> rs485-rx-during-tx;
>
> Asserts the RTS signal low active just fine...
>
> Is this a known problem? Any idea where that could come from? It looks
> as if the receiver part is actually enabling RTS...?
Which kernel version do you use? My latest rs485 related patches went
into v4.17-rc1. With that I managed to make rs485 half duplex work on
several customer boards.
> Also, isn't enabling RX even in half-duplex mode quite common in order
> to detect collisions?
I don't know.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
WARNING: multiple messages have this Message-ID (diff)
From: u.kleine-koenig@pengutronix.de (Uwe Kleine-König)
To: linux-arm-kernel@lists.infradead.org
Subject: serial: imx: half-duplex RS485 operation with RTS active low
Date: Mon, 16 Apr 2018 11:22:57 +0200 [thread overview]
Message-ID: <20180416092257.frbmooduhm4zrhhl@pengutronix.de> (raw)
In-Reply-To: <0e88706a05a302201be396d2f03c3e9e@agner.ch>
Hi Stefan,
On Mon, Apr 16, 2018 at 11:14:32AM +0200, Stefan Agner wrote:
> Using upstream I noticed that RS-485 does not work in the default
> configuration for our platforms (Toradex Apalis/Colibri). Closer
This is an i.MX6?
> debugging shows that it is related to "serial: imx: default to half
> duplex rs485".
>
> We use the i.MX UART in DTE mode and control the RS-485 transceiver
> using the RTS signal in low-active mode.
>
> uart-has-rtscts;
> fsl,dte-mode;
> linux,rs485-enabled-at-boot-time;
> rs485-rts-active-low;
That means you're not using a GPIO for RTS signaling, right?
> Using this setting leads to the RTS signal not getting asserted (the
> oscilloscope only shows a very short fluke before the start bit is
> sent).
>
> However, using
>
> uart-has-rtscts;
> fsl,dte-mode;
> linux,rs485-enabled-at-boot-time;
> rs485-rts-active-low;
> rs485-rx-during-tx;
>
> Asserts the RTS signal low active just fine...
>
> Is this a known problem? Any idea where that could come from? It looks
> as if the receiver part is actually enabling RTS...?
Which kernel version do you use? My latest rs485 related patches went
into v4.17-rc1. With that I managed to make rs485 half duplex work on
several customer boards.
> Also, isn't enabling RX even in half-duplex mode quite common in order
> to detect collisions?
I don't know.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-K?nig |
Industrial Linux Solutions | http://www.pengutronix.de/ |
next prev parent reply other threads:[~2018-04-16 9:22 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-16 9:14 serial: imx: half-duplex RS485 operation with RTS active low Stefan Agner
2018-04-16 9:14 ` Stefan Agner
2018-04-16 9:22 ` Uwe Kleine-König [this message]
2018-04-16 9:22 ` Uwe Kleine-König
2018-04-16 10:29 ` Stefan Agner
2018-04-16 10:29 ` Stefan Agner
2018-04-16 13:01 ` Stefan Agner
2018-04-16 13:01 ` Stefan Agner
2018-04-16 13:42 ` Uwe Kleine-König
2018-04-16 13:42 ` Uwe Kleine-König
2018-04-16 16:12 ` Stefan Agner
2018-04-16 16:12 ` Stefan Agner
2018-04-16 18:02 ` Uwe Kleine-König
2018-04-16 18:02 ` Uwe Kleine-König
2018-04-16 9:54 ` Einar Vading
2018-04-16 9:54 ` Einar Vading
2018-04-16 9:57 ` Einar Vading
2018-04-16 9:57 ` Einar Vading
2018-04-16 10:35 ` Stefan Agner
2018-04-16 10:35 ` Stefan Agner
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