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How to use UARTs

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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/ttyS0*UART2: /dev/ttyS1*UART3:/dev/enttyS2*UART4: /dev/ttyS3IGEP Uart devices have the following names in Kernel [[Linux Kernel 2.6.37.y|2.6.wikipedia37.orgy]]:*UART1: /dev/ttyO0*UART2: /dev/ttyO1*UART3: /dev/wikittyO2*UART4: /UART UART]. dev/ttyO3
'''Note''': This program have a debug option using GPIOs to debug via oscilloscope, this option is useful to learnt about the Kernel latencies and IRQ. Debug has set to "write" and "select" functions.
= Feedback == Configure UART1 and Contributing UART3 in IGEP with RS232 levels on J960 connector ===
At any point, if you see a mistake you can contribute to this How-To==== Edit igep. ini file ====
= Preparing IGEP =To test UARTs we use UART1 (dev/ttyO0) and UART3 (dev/ttyO2) via J960 connector using RS232 standard.
=== Configure IGEP === To test UARTs we use *UART1 (dev/ttyS0) and UART3 (dev/ttyS2) via J960 connector using RS232 standard.  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]].  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" width="200"
|-
| style[[Image:RS232 Schematic Igep V2.png|800x531px]]|} <br>  === Uart Schematic Igep Module === {| cellspacing="text-1" cellpadding="1" width="200" border="1" align: left;="center" |-| [[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 test make with UART:
Some tests do it:  === Decode Characters === Decoded with [http://www.asciitable.com/ ASCII table].  {| cellspacing="1" cellpadding="1" width="200" border="1" align="center"|-| [[Image:Uart decode1withlf.JPG|350x230px]] | [[Image:Uart decode0withlf.JPG|350x230px]] | [[Image:Uart decode100000withlf.JPG|350x230px]]|-| Decoding "1\n" | Decoding "0\n" | Decoding "100000\n"|} Click to enlarge image  === select timeout === 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>  {| cellspacing="1" cellpadding="1" width="200" border="1" align="center"|-| [[Image:Uart select timeout9.JPG|350x230px]]|-| UART1=Blue and UART3=Green|} Click to enlarge image  === RS232 Voltage params === More information [http://en.wikipedia.org/wiki/RS-232#Standard_details here].  {| cellspacing="1" cellpadding="1" width="200" border="1" align="center"|-| [[Image:Uart voltageparams8.JPG|350x230px]]|-| Vpp=11.8V aprox , Vmin=-5.6V aprox|} Click to enlarge image  === Speed Overview === Note that wave is degraded when speed is higher  {| cellspacing="1" cellpadding="1" width="200" border="1" align="center"|-| [[Image:Uart 300 o.JPG|260x172px]] | [[Image:Uart 4800 o.JPG|260x172px]] | [[Image:Uart 115200 o.JPG|260x172px]] | [[Image:Uart 3000000 o.JPG|260x172px]]|-| Overview signal to 300 bauds | Overview signal to 4800 bauds | Overview signal to 115200 bauds | Overview signal to 3000000 bauds|-| [[Image:Uart 300 s.JPG|260x172px]] | [[Image:Uart 4800 s.JPG|260x172px]] | [[Image:Uart 115200 s.JPG|260x172px]] | [[Image:Uart 3000000 s.JPG|260x172px]]|-| Specific wave to 300 bauds | Specific wave to 4800 bauds | Specific wave to 115200 bauds<br> | Specific wave to 3000000 bauds<br>|} Click to enlarge image
=== 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;
 
{| cellspacing="1" cellpadding="1" width="200" border="1" align="center"
|-
| [[Image:Uart lag left6.JPG|350x230px]]
| [[Image:Uart lag right7.JPG|350x230px]]select: blocked until all data is available.
|-
| Lag between UART1 and UART3 (300 bauds)
| Lag between UART3 and UART1 (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 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>
 
{| cellspacing="1" cellpadding="1" width="200" border="1" align="center"
|-
| [[Image:Uart select5.JPG|260x172px]]
| [[Image:Uart select to write1.JPG|260x172px]]
| [[Image:Uart write2.JPG|260x172px]]
| [[Image:Uart write to select0.JPG|260x172px]]
|-
| select function time
| Time between select and write
| write function time
| Time between write and select
|}
 
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.
 
{| 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>
|}
<pre>{| cellspacing="1" cellpadding="1" border="1" align="center" width="200"&lt;br&gt;|-&lt;br&gt;| [[Image:Connector used readwrite test.JPG|center|350x230px]] &lt;br&gt;| &lt;br&gt;[[Image:All connected readwrite test.JPG|center|350x230px]] &lt;br&gt;&lt;br&gt;|}</pre> '''Under Construction'''
[[Category:Communications]] [[Category:Work_in_progress]] [[Category:How_to_forgeUART]]
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