Enabling UART3 for serial communication on i.MX8M Mini Evk

[abhijit_thorat]

I am using Android pie (android_p9.0.0_1.0.0-ga_image_8mmevk) on i.MX8M Mini EVK

I want use UART for my Application development.

As per document IMX8MMEVKHUG.pdf UART3 can be accessible from Expansion header(J1103) (Pin No.7, 8, 9, 10, 11)

Can you please guide me how to enable UART3 on i.MX8M Mini EVK and how to use it to send and receive data?

I think /dev/ttymxc2 is for UART3

But when I try to configure it I get following error:

stty -F /dev/ttymxc2 115200 raw -echo

stty: /dev/ttymxc2: Permission denied

Why I am getting such kind of error?

Is there any way to enable UART without compiling any other source code or kernel code. Please help me to solve this issue.

Attached IMX8MMEVKHUG.pdf and boot logs for reference.

[abhijit_thorat]

Hi igorpadykov,

Thanks for your reply.

I am successfully able to use Android NDK and run and execute sample hello app on this iMX board.

1. But instead of using NDK i want to cross compile C / C++ code using some tool-chain or some other method and execute it it on target hardware i.e iMX8M Mini EVK.
   As per my understanding on embedded Linux we need tool-chains and sysroot to cross compile any program or libraries but i am new to Embedded Android so i am not understanding how to do the same thing in Android.
   Basically I want to know how to cross compile C code for android without NDK.
2. Also After my boards boots up when i try to execute basic commands such as sudo or vi or vim or dmesg on iMX8M mini then it gives me errors like - su: invalid uid/gid 'dmesg'    or commands not found etc.. Even GCC is also not available i think,

Can you please guide me?

Thanks,

Abhijit

[igorpadykov]

Hi Abhijit

for new questions recommended to create new thread.

Best regards
igor

[abhijit_thorat]

Hi,

I have created new thread.
Please check link ; https://community.nxp.com/message/1166679 

Thanks,

Abhijit

[abhijit_thorat]

Hi igorpadykov,

Thanks for your reply.

But I want to just test UART first without creating any android application. Like using echo command.

I tried following but it didn't work.

stty -F /dev/ttymxc2 115200 raw -echo

stty: /dev/ttymxc2: Permission denied

echo Hello World > /dev/ttymxc2

Like this I want to test UART. Do you know how to this?

[igorpadykov]

Hi Abhijit

uart can be tested in linux using unit test:

mxc_uart_test\test - imx-test - i.MX Driver Test Application Software 

Best regards
igor

[abhijit_thorat]

Hi igorpadykov,

I am able to test UART from the link you provide.

mxc_uart_test\test - imx-test - i.MX Driver Test Application Software 

I use Android NDK to run this code.

But to before accessing UART I have to run following commands manually.

1. su

Command to get root access

2. setenforce 0

To turn off SELinux (Security Enhanced Linux)

3. chmod 777 /dev/ttymxc2

Command to set permissions for port /dev/ttymxc2. This is the device file for UART pins on NXP platform.

4. stty -F /dev/ttymxc2 115200 raw -echo

Command to set Baud rate to 115200

Is there any way so that I can avoid run these commands manually. Can I do these settings from Android application only?

Can you please guide me?

Following is the JNI file code from which UART is accessed. Is it a proper way to access UART? or I should do it differently? 

#include <jni.h>
#include <string>
#include "simple.h"
#include "uart_test.h"
#include <android/log.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include "uart_test.h"
#include <android/log.h>
#include <errno.h>

#define LOOPBACK   0x8000
#define MESSAGE       "Test Hello good evening bruviti\0"
#define MESSAGE_SIZE   sizeof(MESSAGE)
#define MESSAGE1      "Test message\0"
#define MESSAGE_SIZE1  sizeof(MESSAGE1)

#define APPNAME "uart_test"

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_temp_MainActivity_stringFromJNI(JNIEnv *env, jobject instance) {
    std::string hello = PrintHello();


    printf("********************************************** In MYUART ************************************* \n");

    int uart_file1;
    unsigned int line_val;
    char buf[5];
    struct termios mxc, old;
    int retval = 0;
    int retries = 5;


    if ((uart_file1 = open("/dev/ttymxc2", O_RDWR)) == -1) {
        __android_log_print(ANDROID_LOG_VERBOSE, APPNAME, "Error opening /dev/ttymxc2 ------------ %d\n", errno);
    }
    else {
        __android_log_print(ANDROID_LOG_VERBOSE, APPNAME, "/dev/ttymxc2 opened %d", uart_file1);
    }

    tcgetattr(uart_file1, &old);
    cfsetispeed (&old, B115200);
    cfsetospeed (&old, B115200);
    mxc = old;
    mxc.c_lflag &= ~(ICANON | ECHO | ISIG);

    mxc.c_iflag &= ~(IGNBRK | BRKINT | ICRNL |
                     INLCR | PARMRK | INPCK | ISTRIP | IXON);
    mxc.c_cflag |= CSTOPB;
    mxc.c_cflag = ~CSIZE | CS8;
    mxc.c_cflag &= ~PARENB;
    mxc.c_oflag = 0;
    mxc.c_lflag &= ~(ECHO | ECHONL | ICANON | IEXTEN | ISIG);
    mxc.c_cc [VMIN]=30;
    mxc.c_cc [VTIME]=100;

    tcsetattr(uart_file1, TCSANOW, &mxc);
    __android_log_print(ANDROID_LOG_VERBOSE, APPNAME, "Attributes set\n");


    line_val = LOOPBACK;
    ioctl(uart_file1, TIOCMSET, &line_val);
    __android_log_print(ANDROID_LOG_VERBOSE, APPNAME, "Test: IOCTL Set\n");


    tcflush(uart_file1, TCIOFLUSH);

    write(uart_file1, MESSAGE, MESSAGE_SIZE);
    __android_log_print(ANDROID_LOG_VERBOSE, APPNAME, "Data Written= %s\n", MESSAGE);

    sleep(1);
    memset(buf, 0, MESSAGE_SIZE);
    while (retries-- && retval < 5)
        retval += read(uart_file1, buf + retval, MESSAGE_SIZE - retval);
    __android_log_print(ANDROID_LOG_VERBOSE, APPNAME, "Data Read back= %s\n", buf);

    sleep(2);
    ioctl(uart_file1, TIOCMBIC, &line_val);

    retval = tcsetattr(uart_file1, TCSAFLUSH, &old);

    close(uart_file1);

    if (memcmp(buf, MESSAGE, MESSAGE_SIZE)) {
        __android_log_print(ANDROID_LOG_VERBOSE, APPNAME, "Data read back %s is different than data sent %s\n",
                            buf, MESSAGE);
    }

    return env->NewStringUTF(hello.c_str());

}

[igorpadykov]

Hi Abhijit

configuring permissions can be found on general android resources like:

https://developer.android.com/things/sdk/pio/uart 

Best regards
igor
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[abhijit_thorat]

Hi igorpadykov,

As per your post

"configuring permissions can be found on general android resources like:

https://developer.android.com/things/sdk/pio/uart  "

I checked this sample example. But this example is for boards having Android Things only and not other android.

How can i check for other Android BSP. I am using Android pie (android_p9.0.0_1.0.0-ga_image_8mmevk) on i.MX8M Mini EVK

i.MX8M Mini EVK is not in supported in hardware lists for Android Things. So I cannot flash Android Things.

If you can guide me to solve 'stty: /dev/ttymxc2: Permission denied' issue it will be easy for me to test UART.

Can you please guide me?

Thanks,

Abhijit