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Old 08-31-2018, 08:14 AM   #1
ptz
LQ Newbie
 
Registered: Aug 2016
Posts: 2

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Unable to use hardware flow control on UART


I am trying to use hardware flow control on serial port ttyS1. The underlying reason I want RTS to be asserted during a write is that the relevant pin is connected to an external RS485 half-duplex transceiver that is set to write mode by a high signal. I tried configuring the port with
Code:
struct termios options;
options.c_cflag |= CRTSCTS;
But this has no effect on the relevant pin. I'm on kernel 4.14.0.

I also tried setting the pin to 1 manually from user-space via
Code:
fprintf()
to the exported gpio. This does assert the signal, but
Code:
write()
returns long before the entire data has actually hit the wire.

Me asking the questions elsewhere for reference:
https://unix.stackexchange.com/quest...ly-output-data
https://unix.stackexchange.com/quest...led-rts-on-tty
 
Old 09-04-2018, 08:00 AM   #2
smallpond
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Registered: Feb 2011
Location: Massachusetts, USA
Distribution: CentOS 6 & 7
Posts: 3,270

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You may also want to set CLOCAL when not using a modem.
 
  


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rts, serial port, tty, uart


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