Changes

= Overview<br> =

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'''Note''': This program has a debug option using GPIOs to debug via oscilloscope, this option is useful to learnt about the Kernel latencies. Debug has set to "write" and "select" functions.

= Feedback and Contributing =

= Preparing IGEP =

To test UARTs we use UART1 (dev/ttyS0) and UART3 (dev/ttyS2) via J960 connector using RS232 standard.

</pre>

By default, UART3 is used by Kernel serial console, we need to disable it, go to igep.ini file, comment next line: <br>

=== Check UARTs devices ===

If you don't have setserial installed type:

<pre>apt-get install setserial</pre>

=== Connect peripherals ===

(Connect to 3) o---| 9 10 |---x (Not used)

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=== Send some data ===

Type something in one terminal.

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=== Uart Schematic Igep Module ===

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| [[Image:Uart Schematic Igep Module.png|581x600px]]

= Compile and run program =

As explained above, the program uses GPIO for debug option via oscilloscope, it is necessary install user-gpio-drv.ko driver inside Linux Kernel, more information [[How to use GPIOs|here]] .

Once you have installed module. Compile program using your Cross Compiler, I used arm-linux-gnueabi-:

= Testing UART =

Decoded with [http://www.asciitable.com/ ASCII table].

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Program sends information via UART1 but don't receive response via UART3, because only a process is executed. This problem is repeated every 5 seconds (constant WAIT=5) until other process sends information via UART3 at the same speed. If "select" hasn't been implemented, process would have stayed blocked.<br>

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More information [http://en.wikipedia.org/wiki/RS-232#Standard_details here].

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Note that wave is degraded when speed is higher

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| [[Image:Uart 300 o.JPG|260x172px]]

You can see that RS232 have some lag between transmisions. This caused mainly by kernel process management. UART peripheral is controlled by Linux and It isn't a [http://en.wikipedia.org/wiki/Real-time_operating_system real-time operating system].&nbsp;

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This program have three I/O functions that connect to UART driver via ioctl: (read(), write() and select()). But select() and write() change process stat to sleep mode until system don't receive or transmit all information via UART. "select" function is used to prevent that read function can be blocked when data aren't available. <br>The next images (program with debug_gpio enabled and 300 bauds speed) show when process is executed or is waiting. Blue=UART1, Violet="write" and Green="select". When GPIO has HIGH value, process is blocked.<br>

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| [[Image:Uart select5.JPG|260x172px]]

Every full process the number is increased twice. Program checks that this condicion is true, if it isn't accomplished, process will be finish.

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| [[Image:Uart error test2.png|640x400px]]