Difference between revisions of "Serial ports usage on Linux"

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How to use the serial ports on Linux.
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How to use the APF's serial ports on Linux.
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==Generalities==
  
 
On Linux all serial ports are driven the same way with their device nodes:
 
On Linux all serial ports are driven the same way with their device nodes:
−
* ''/dev/ttySMXn'' for i.MX own ports (''/dev/ttySMX0'' is the default console on which you can interact with the board)
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* ''/dev/ttySMXn'' for i.MX processor internal ports
 
* ''/dev/ttyUSBn'' for USB <-> serial converters
 
* ''/dev/ttyUSBn'' for USB <-> serial converters
 
* ''/dev/ttySn'' for 16550 compatible FPGA's IP
 
* ''/dev/ttySn'' for 16550 compatible FPGA's IP
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 +
==/dev/ttySMX0==
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* ''/dev/ttySMX0'' is the default console on which you can interact with the board (U-Boot and Linux).
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* So: without software modifications this port is not usable to connect a MODEM or any other RS232 device. If you want to use it a normal serial port on Linux then:
 +
** be sure that your device won't send data back in response of U-Boot boot's sequence
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** change ''console=ttySMX0,115200'' to ''console=ttySMXN,115200'' in U-Boot ''bootargs'' variable (N=1 on APF9328 and 2 on APF27)
  
 
==Changing port parameters==
 
==Changing port parameters==
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-brkint ixoff -imaxbel
 
-brkint ixoff -imaxbel
 
-iexten -echoctl
 
-iexten -echoctl
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</pre>
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* Change Baud rate to 115200 of port 2:
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<pre class=apf>
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stty -F /dev/ttySMX2 115200
 
</pre>
 
</pre>
  

Revision as of 08:07, 24 June 2009

How to use the APF's serial ports on Linux.

Generalities

On Linux all serial ports are driven the same way with their device nodes:

  • /dev/ttySMXn for i.MX processor internal ports
  • /dev/ttyUSBn for USB <-> serial converters
  • /dev/ttySn for 16550 compatible FPGA's IP

/dev/ttySMX0

  • /dev/ttySMX0 is the default console on which you can interact with the board (U-Boot and Linux).
  • So: without software modifications this port is not usable to connect a MODEM or any other RS232 device. If you want to use it a normal serial port on Linux then:
    • be sure that your device won't send data back in response of U-Boot boot's sequence
    • change console=ttySMX0,115200 to console=ttySMXN,115200 in U-Boot bootargs variable (N=1 on APF9328 and 2 on APF27)

Changing port parameters

  • Get current parameters:
# stty -F /dev/ttySMX0
speed 115200 baud;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = ^J;
eol2 = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W;
lnext = ^V; flush = ^O; min = 1; time = 0;
-brkint ixoff -imaxbel
-iexten -echoctl
  • Change Baud rate to 115200 of port 2:
stty -F /dev/ttySMX2 115200

Sending/Receiving data

  • It is simple as opening the device as a file and writing data to it:
# echo "HELLO" > /dev/ttySMX0
  • To receive data (ASCII in that case):
# cat /dev/ttySMX0
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