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>; //four pins RX,TX,CTS,RTS
fsl,uart-has-rtscts;
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. If I have understood the RTS/CTS system correctly
the RTS signal should be toggled immediately after the stopbit is sent.
So that 13 ms (from the logic analyzer image) are really unnecessary and
I can not trace it back where they are from. With other baudrates it is
no less and no more than the 13 ms (~2...18ms-spread inside of the same
baudrate)
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 is 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) ?
image logic analyzer:
https://community.freescale.com/servlet/JiveServlet/download/398158-274040/auart0_rts.png
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