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Linux Kernel Module for UART

aly mohamed
Prodigy 110 points
Other Parts Discussed in Thread: AM3358

Dear all,

I m starting Development on AM335x Starter Kit. It's Cortex M3 Processor in AM3358 ZCZ Package. I m running Linux on target and got the " Run Modus Debug "  working. When my User Application uses a Method to print somthing out like  printf("Hello World from Sitara") everything works fine . But when i try to get the UARTECHO Example running while Linux is running the process is beeing killed. I suppose the kernel is preventing my User Application from accessing UART . Notice the following Schematic :

My task what i have to do is simple : My Application which will run on the AM3358 SK Board has to communicate through a serrial connection (UART) with a host PC. The host sends the Commands through serial port, the Application recieves that and  exectutes something, and sends  Answers back to the Host. 

In the Schematic we can see that there are UART0 , UART1 available. My Questions are:

1) - Why is my Application beeing stopped when i m trying to access the Processors Register using  HWREG( something)  |=  something  ??? 

2)- How could i find out which Devices (UART , Timer , Spi, .. )  are already initialized or used by the Kernel, and which of them i can use for my Application and which not ? ( Source Code in the SDK would be helpful ? )

3)- When i want to access Registers to initalize a UART or SPI , does that mean that i have to do it as a Kernel Module ?? or in another privileged Mode ? 

4)- Which is the easiest way to make the Commuication between my Application work ? Which UART do i have to use? UART0, UART1 ? if UART1 How could i connect  UART 1 on the board ? I m planing to use UART0 because its connected to USB0, but i don't know it that will work ..

5)- From my Remote Terminal connected to the Target when i look in /dev/ ... i do not find any ttyS0 there is just tty0 .. so is UART0 , UART1 ready and initialized in the kernel so all what i have to do to get access to /dev/tty* and read and write the Data from it , or do i have to initialize it first ??

6)- If i programmed a Kernel Device Driver to initialize UART and tried to do  HWREG( something)  |=  something would that work ? or is there another way to initalise a device in linux ? (Source Code initalizing a Device in SDK would be helpful ! )

7)- How would the Device Interrupt work with my Application, to tell it that there is Data to read in ttyS0 as example?

8)- Where the hell in SDK can i find the some Device Driver Code witch would initalize a uart , timer or any thing used by the kernel ? i guess the source code is in / user/ ti-sdk-am335x-evm-05.06.00.00/board-support/linux-3.2.0-psp05.06.00.00

You don't have to answer all the Questions, i just wrote them to make my Problem clear. 

best regards




  • 0
    TI__Mastermind 25235 points

    Hi,

    It seems like you are trying to run a StarterWare example (UARTECHO) on top of Linux. This is not possible. I will try to answer all of your questions so that it may become clearer to you.

    1) - StarterWare is OS-less software to provide basic functionality for the AM335x devices. It allows direct access to the processor registers via the HWREG() macro. Trying to use this macro on top of the Linux kernel is not possible. The kernel prevents user space applications from directly accessing the processor registers.

    2) - You can navigate to <path_to_linux_sources>/arch/arm/mach-omap2/board-am335xevm.c file. Function setup_starterkit() is the init function for the Starter Kit. The struct evm_dev_cfg evm_sk_dev_cfg[] structure contains pointers to other functions, which initialize some of the peripherals and pinmux the needed pins.

    3) - Initializing the UART or SPI modules doesn't require a new kernel module. You can do it inside the board-am335xevm.c file I mentioned. Just create a new pinmux config for the needed peripheral (if it doesn't already exist) and add it to the evm_sk_dev_cfg[] structure, which is used during initialization. Be sure to check for pinmux conflicts.

    4) - UART0 is by default used for the serial console and it is passed through an FTDI chip, so that you can access it via USB. The only other UART that is pinned out on the Starter Kit is UART2, which can be pinmuxed (TTL signal level) to the ZIGBEE J11 header, which is not populated on the board. Please refer to the Starter Kit schematics for more information about this header pinout. Schematics can be found here.

    5) - The tty ports on the OMAP are named ttyO* and not ttyS* since a few kernel releases ago. ttyO0 through ttyO5 are always shown in /dev/ even if not initialized. The reason is easier detection. In order to use a tty interface, you need to first initialize the corresponding module (I already explained how).

    6) - This should be clear by now.

    7) - The communication is handled by the Termios protocol. I don't think you should do anything else.

    8) - This should also be clear by now.

    Best regards,
    Miroslav

  • 0 in reply to Miroslav Kiradzhiyski XID
    Prodigy 110 points

    Miroslav Kiradzhiyski XID said:

    4) - UART0 is by default used for the serial console and it is passed through an FTDI chip, so that you can access it via USB. The only other UART that is pinned out on the Starter Kit is UART2, which can be pinmuxed (TTL signal level) to the ZIGBEE J11 header, which is not populated on the board. Please refer to the Starter Kit schematics for more information about this header pinout. Schematics can be found here.

    Hi Miro, 

    i have a small problem here, beacause the ZIGBEE Header is connected to SPI0 , and my Application also needs this SPI for an external chip (TRF7970)

    so the only choice remains is to use UART0 !

    i m running "Run Modus Debug" and it is required to connect the small cable (USB0) to the host because of the Debugger. Am i right !?!?

    so since there is a FTDI Chip we have two Interfaces (JTAG,UART0) ..  (see the second Schematic Pic above )

    If i want to use UART0 with my Application while debugging , so the only thing i have to do is not connecting from Host via "Remote Ssh Terminal" in Code Composer or using Minicom to connect to Target , because both ( or one of them !?!?) are using UART0.. and so i can sent my Commands via UART0 to the Board and debug via JTAG simultaneosly ??!?!?!

    am i right with that ?

    best regards

    aly 

  • 0 in reply to aly mohamed
    TI__Mastermind 25235 points

    Hi Aly,

    Yes, you are correct.

    Best regards,
    Miroslav

  • 0 in reply to Miroslav Kiradzhiyski XID
    Prodigy 110 points

    Hi Miro,

    thnx a lot :)

    best regards 

    aly

  • 0 in reply to Miroslav Kiradzhiyski XID
    Prodigy 135 points

    Hi Miroslav,

    I'm trying to access the UART via /dev/ttyO0 in Linux (the version that came with the AM335x EVM, SDK v05.00.00) using CCS6. Your answer is the closest that I've seen address this issue...

    Anyway, the termios.h that I found under \ti\ccsv6\tools\compiler\gcc-arm-none-eabi-4_7-2013q3\arm-none-eabi\include\termios and ...\include\sys\termios.h are practically empty. Do you know where I can get the proper headers for termios?

    Thanks,

    Tom

  • 0 in reply to Nhattrieu Duong
    Prodigy 135 points

    I was able to figure this out. I was using the headers in ccsv6 when I should have been using those in ti-sdk-am355x-evm-07.00.00.00/board-support/linux-3.12.10-ti2013.12.01 (duh!)