On Mon, Apr 16, 2018 at 11:14:32AM +0200, Stefan Agner wrote:
> Hi,
>
> Using upstream I noticed that RS-485 does not work in the default
> configuration for our platforms (Toradex Apalis/Colibri). Closer
> debugging shows that it is related to "serial: imx: default to half
> duplex rs485".
We where struggling a bit with half duplex rs485 too a while ago.
>
> 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;
>
> 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).
I think this is what we had too. But if I recall we where supposed to be
active-high but I think the behavior is the same either way.
>
> 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...
We have a (RTS active high) configuration working for us now with only
uart-has-rtscts
in DT, and then when using the port we do
struct serial_rs485 rs485conf;
memset(&rs485conf, 0x00, sizeof(struct serial_rs485));
rs485conf.flags |= SER_RS485_ENABLED;
rs485conf.flags |= SER_RS485_RTS_ON_SEND;
rs485conf.flags &= ~(SER_RS485_RTS_AFTER_SEND);
f_debug("Calling ioctl...");
if (ioctl (fd, TIOCSRS485, &rs485conf) < 0) {
f_critical("ioctl serial_rs485 failed");
return -1;
}
Hope it helps.
>
> Is this a known problem? Any idea where that could come from? It looks
> as if the receiver part is actually enabling RTS...?
>
> Also, isn't enabling RX even in half-duplex mode quite common in order
> to detect collisions?
>
> --
> Stefan
// Einar
>
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