On 2020-05-18 17:22, Lukas Wunner wrote:
On Mon, May 18, 2020 at 06:12:41PM +0300, Andy Shevchenko wrote:
On Sun, May 17, 2020 at 11:56:08PM +0200, Heiko Stuebner wrote:
> From: Heiko Stuebner <heiko.stuebner@xxxxxxxxxxxxxxxxxxxxx>
>
> The RE signal is used to control the duplex mode of transmissions,
> aka receiving data while sending in full duplex mode, while stopping
> receiving data in half-duplex mode.
>
> On a number of boards the !RE signal is tied to ground so reception
> is always enabled except if the UART allows disabling the receiver.
> This can be taken advantage of to implement half-duplex mode - like
> done on 8250_bcm2835aux.
>
> Another solution is to tie !RE to RTS always forcing half-duplex mode.
>
> And finally there is the option to control the RE signal separately,
> like done here by introducing a new rs485-specific gpio that can be
> set depending on the RX_DURING_TX setting in the common em485 callbacks.
...
> + port->rs485_re_gpio = devm_gpiod_get_optional(dev, "rs485-rx-enable",
> + GPIOD_OUT_HIGH);
While reviewing some other patch I realized that people are missing
the
point of these GPIO flags when pin is declared to be output.
HIGH here means "asserted" (consider active-high vs. active-low in
general). Is that the intention here?
Lukas, same question to your patch.
Yes. "High", i.e. asserted, means "termination enabled" in the case of
my patch and "receiver enabled" in the case of Heiko's patch.
But "High" on a gpio would disable the receiver when connected to !RE.
Maarten
