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How to use UARTs

363 bytes added, 11:41, 12 November 2014
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= Overview=<brsection begin=overview /> =This How-To is meant to be a starting point for people to learn use UART for IGEP devices as quickly and easily as possible. In this How-To, we use [http://labs.isee.biz/index.php/Pre-installed_software_on_IGEP_Processor_Boards IGEP Firmware] and a program that use UART peripherals. This How-To was tested in: *[[IGEP firmware Yocto|IGEP firmware Yocto]] and [[Linux_Kernel_2.6.37.y|Kernel 2.6.37.y]] with IGEPv2.
This How-To Example program has a debug option using GPIOs to debug via oscilloscope, this method is meant to be a starting point for people useful to learn use UART for IGEP v2 devices as quickly and easily as possibleabout the Kernel latencies. In this how-Debug has set to, we use [http://releases.linaro.org/platform/linaro-m/headless/final/linaro-m-headless-tar-20101108-2"write" and "select" functions.tar.gz Linaro Headless] with [[Linux Kernel 2.6.35.yPeripherals Summary#UART|Kernel 2.6.35.yMore information]] and UART test program. This program is executed twice, at the same time inside the same IGEP. Its function is get a number via UART, increase it and send result to other UART, the result will be a infinite loop between 2 UARTs. '''(upload source code)''' <section end=overview />
More information about = Preparing IGEP =IGEP Uart devices have the following names in Kernel [http[Linux Kernel 2.6.35.y|2.6.35.y]]:*UART1:/dev/en.wikipedia.orgttyS0*UART2: /wikidev/UART UART]. ttyS1*UART3: /dev/ttyS2'''Note'''*UART4: This program /dev/ttyS3IGEP Uart devices have a debug option using GPIOs to debug via oscilloscope, this option is useful to learnt about the following names in Kernel latencies[[Linux Kernel 2.6.37.y|2.6. Debug has set to "write" and "select" functions37.y]]:*UART1: /dev/ttyO0= Feedback and Contributing =*UART2: /dev/ttyO1*UART3: /dev/ttyO2At any point, if you see a mistake you can contribute to this How-To. *UART4: /dev/ttyO3
= Preparing IGEP =
=== Configure UART1 and UART3 in IGEP with RS232 levels on J960 connector ===
To test UARTs we use UART1 (dev/ttyS0) and UART3 (dev/ttyS2) via J960 connector using RS232 standard==== Edit igep. ini file ====
NOTE: Make sure that you installed open SSH server. If you don't have it go [[How to forge a local file system server with IGEP0020 board#Installing_Open_SSH_Server|here]]To test UARTs we use UART1 (dev/ttyO0) and UART3 (dev/ttyO2) via J960 connector using RS232 standard.
By default, *UART1 is can used by RS485 driver, we need to disable it, edit igep.ini file: <br> <pre>board.ei485= yes</pre> *UART1 is configured in RS232 driver, when igep line is replaced by (or type in -Maybe you don't found this line, replaced by or type this-):<br> <pre>board.ei485= no</pre> *By default, UART3 is used by Kernel serial console, we need to disable it, go to igep.ini file, comment next line: <br> <pre>;console=ttyS2ttyO2,115200n8;console=ttyO</pre>==== Edit inittab file ====Getty program uses /dev/ttyO2 in IGEP Firmware, disable it modifying /etc/inittab file:*Comment next line:<pre> #S:2345:respawn:/sbin/getty 115200 ttyO2</pre>
=== Check UARTs devices ===
<pre>dmesg | grep tty</pre>
The result will be similar at that:
<pre>root@localhostigep00x0:~/PROGRAM# dmesg | grep tty
[ 0.000000] console [tty0] enabled
[ 0.598999485198] serial8250omap_uart.0: ttyS0 ttyO0 at MMIO 0x4806a000 (irq = 72) is a ST16654OMAP UART0[ 0.784057485565] serial8250omap_uart.1: ttyS1 ttyO1 at MMIO 0x4806c000 (irq = 73) is a ST16654OMAP UART1[ 0.969085485931] serial8250omap_uart.2: ttyS2 ttyO2 at MMIO 0x49020000 (irq = 74) is a ST16654OMAP UART2[ 10.153503486267] serial8250omap_uart.3: ttyS3 ttyO3 at MMIO 0x49042000 (irq = 80) is a ST16654root@localhost:~/PROGRAM# </pre> Get information about UARTs, type: <pre>setserial -g /dev/ttyS[0123]</pre> The result will be similar at that: OMAP UART3<pre>root@localhostigep00x0:~/PROGRAM# setserial -g /dev/ttyS[0123]/dev/ttyS0, UART: 16654, Port: 0x0000, IRQ: 72/dev/ttyS1, UART: 16654, Port: 0x0000, IRQ: 73/dev/ttyS2, UART: 16654, Port: 0x0000, IRQ: 74/dev/ttyS3, UART: 16654, Port: 0x0000, IRQ: 80root@localhost:~/PROGRAM# </pre> If you don't have setserial installed type: <pre>apt-get install setserial</pre>
=== Connect peripherals ===
Connect IGEPv2 board using J960 connector like this:
<pre> J960
------
(Not used) x---| 1 2 |---o (Connect to 8)
(Connect to 9) o---| 3 4 |---x (Not used)
(Not used)x---| 7 8 |---o (Connect to 2)
(Connect to 3) o---| 9 10 |---x (Not used)
------ </pre> 
=== Send some data ===
Use minicom microcom to prove it, open two terminals via SSH&nbsp;and log with root user:
Terminal 1:
<pre>minicom -D microcom /dev/ttyS0ttyO0</pre>
Terminal 2:
<pre>minicom -D microcom /dev/ttyS2 ttyO2 </pre> Type something in one terminal.  = Schematics = === RS232 Schematic Igep V2 === {| cellspacing="1" cellpadding="1" border="1" align="center"|-| [[Image:RS232 Schematic Igep V2.png|800x531px]]|} <br>  === Uart Schematic Igep Module ===
{| cellspacing="1" cellpadding="1" width="200" border="1" align="center" width="200"
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| style="text-align: left;" | [[Image:Minicom screenshotUart Schematic Igep Module.png|640x400px581x600px]]
|}
= Compile and run program =
As explained above, the program uses GPIO for debug option via oscilloscope, it is necessary install userDownload [http://labs.isee.biz/index.php/File:Uart-test-gpio2-drvbeta1.tar.ko driver inside Linux Kernel, more information [[How to use GPIOs|here]bz2 program source] and extract it.  There Before compiling the program, there are some interesting things that is interesting to configure, before compiling the program. Open it, program and seek next lines:
<pre>//Define Array char size
#define SIZE 30
 
//Define Debug mode:0==Disable
#define DEBUG 0
//Set GPIO Debugger port
//Be sure that mux is correctly configured and GPIOs are not used
#define GPIO1 136158#define GPIO2 137 162</pre> Constant SIZE: it determine determines the max number of char than can be sent<br>chars sended.
Constant DEBUG: it can break program infinite loop part, it can be useful to debug some errors, : 0 like (infinite loop ) or positive number determine determines loop max entrances<br>.
Constant WAIT: configure it configures select max timein seconds.
Constants GPIO1 and GPIO2: they configure GPIOs used for debug via oscilloscope. Take care to configure By default, 158 and 162 values are not used in IGEPv2. Configure [[Mux configuration|mux and don't ]] properly if you use this GPIO for other purposes<br>GPIOs.
Once you have installed module. Compile program source code using your Cross Compiler, I used arm-linux-gnueabi-a [[How to setup a cross compiler|cross compiler]] for example IGEP SDK: <pre>arm-poky-linux-gnueabi-gcc uart-test-2-beta1.c -o uart-test-beta1 </pre>
= Testing UART =
Some tests do it:
=== Decode Characters ===
Decoded with [http://www.asciitable.com/ ASCII table].
{| widthcellspacing="2001" cellspacingcellpadding="1" cellpaddingwidth="1200" border="1" align="center"
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| [[Image:Uart decode1withlf.JPG|350x230px]]
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=== select timeout ===
The program send Program sends information via UART1 but don't receive a response via UART3, because only a process is executed. This problem is repeated every 5 seconds (constant WAIT=5) until other process is executed sending sends information via UART3at the same speed. If "select " hasn't been implemented, process would have stayed blocked.<br>
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| [[Image:Uart select timeout9.JPG|350x230px]]
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=== RS232 Voltage params ===
More information [http://en.wikipedia.org/wiki/RS-232#Standard_details here].
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=== Speed Overview ===
Note that wave is degraded when speed is higher
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| [[Image:Uart 300 o.JPG|260x172px]]
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=== Lag ===
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;
{| widthcellspacing="2001" cellspacingcellpadding="1" cellpaddingwidth="1200" border="1" align="center"
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| [[Image:Uart lag left6.JPG|350x230px]]
| [[Image:Uart lag right7.JPG|350x230px]]select: blocked until all data is available.
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| Lag between UART1 and UART3 (300 bauds)
Click to enlarge image
This program have three I/O functions that connect to UART driver via ioctl: (read(), write() and select()), but . But select() and write() change process stat to sleep mode until system don't receive or transmit all information via UART, the process awake when I/O task is completed. "select" function is used to prevent that reads read function can be blocked when there data aren't data avaliableavailable.<br>The next captures are do it images (program with GPIO debug mode debug_gpio enabled and 300 bauds speed) show when process is executed or is waiting. Blue=UART1, Violet="write function time " and Green="select function time". When GPIO has HIGH value, process is blocked.<br>
{| widthcellspacing="2001" cellspacingcellpadding="1" cellpaddingwidth="1200" border="1" align="center"
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Click to enlarge image <br>  In this case:  select: blocked until all data is available (LF char received).  write: blocked until all data is send to UART buffer.  === Error test === Every full process the number is increased twice. Program checks that this condicion is true, if it isn't accomplished, process will be finish.
Conclusions{| cellspacing="1" cellpadding="1" width="200" border="1" align="center"|-| [[Image: Uart error test2.png|640x400px]]|-| Runs 16h without any transfer error (3000000 bauds)<br>|}
<br> '''Under Construction'''
[[Category:Communications]] [[Category:Work_in_progress]] [[Category:How_to_forgeUART]]
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