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Question asked by chris321 on Apr 24, 2014
Latest reply on Apr 24, 2014 by Fabio Estevam

Hello Community,


I want to use the AUART0 of the i.MX28 with the handshake signals. For this I am using the latest stable Linux Kernel 3.14.1.


The AUART0 part of the device tree:

auart0: serial@8006a000 {
   pinctrl-names = "default";
   pinctrl-0 = <&auart0_pins_a>;
   status = "okay";



So the device tree uses all four pins of this UART. In Linux itself I configure the interface with:

stty -F /dev/ttyAPP0 raw 9600 -echo -echoe -echok -echoctl -echoke crtscts


The UART and the handshake signals are working in principle. But I've noticed a delay between the RTS signal and the stopbit as you can see in the attached figure. I think that 13 ms are really unnecessary and I can not trace it back where they are from.

I tried this too:

stty -F /dev/ttyAPP0 raw 9600 -echo -echoe -echok -echoctl -echoke -crtscts

The bits CTSEN and RTSEN of the UARTAPP_CTRL2 register are toggled, but there is still a something similar on the RTS lines, but now it os no CTS needed.

So my questions are, where are this delays come from?

How can I be sure who is toggling the RTS line (Linux or the i.MX28 hardware module) ?


best regards