Re: [beagleboard] C programing of Uart peripheral in beaglebone black (Linux)

Robert Heller Thu, 18 Jul 2019 06:32:28 -0700

At Thu, 18 Jul 2019 03:45:54 -0700 (PDT) [email protected] wrote:


> 
> 
> 
> Hi,
> 
> I am using Beagle bone black board in Linux Ubuntu, i am new to BBB, i 
> tried to check the programing of UART peripheral in the BBB..
> 
> Exact C - programs i am not able to  found. like simple c program to 
> initialize the UART with baud rate and other information and writing some 
> data using buffer and i should see the data printing on to the mini com..
> 
> please help me...

The UARTs are connected to /dev/ttySn:

UART0 (console header) /dev/ttyS0   -- note: /sbin/agetty is running on this 
port
UART1 P9.24,P9.26      /dev/ttyS1
UART2 P9.21,P9.22      /dev/ttyS2
UART3 P9.42 (tx only)  /dev/ttyS3
UART4 P9.13,P9.11      /dev/ttyS4
UART5 P8.37,P8.38      /dev/ttyS5

In C, these are "files" and can be accessed via file I/O functions:

At a "lowlevel: open(), read(), write(), close(), and ioctl()/termios().
At a "highlevel: fopen(), fread()/fscanf()/fgets(), 
                 fwrite()/fprintf()/fputs(), and fclose().
                 
Unfortunately, the "man" command is not installed in my BBB image, but it
should be there on your Ubuntu machine and all of the C functions listed above
are well documented.

Really simple C program (assumes BB-UART1-00A0.dtbo has been loaded by uBoot 
and you have connected to P9.24 and P9.26):

#include <stdio.h>
#include <termios.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>

#define ERRORCHECK(cmd,message) \
if ((cmd) < 0) {\
   int err = errno; \
   perror(message); \
   exit(err); \
}

int main(int argc, char *argv[])
{
    int ttyfd;
    struct termios saved, current;
    
    ttyfd = open("/dev/ttyS1",O_RDWR);
    ERRORCHECK(ttyfd,"Open of /dev/ttyS1 failed:")
    ERRORCHECK(tcgetattr(ttyfd,&saved),"tcgetattr (saved) of /dev/ttyS1 
failed:")
    ERRORCHECK(tcgetattr(ttyfd,&current),"tcgetattr (current) of /dev/ttyS1 
failed:")
    ERRORCHECK(cfsetspeed(&current,B115200),"cfsetspeed (current) failed:");
    ERRORCHECK(tcsetattr(ttyfd,TCSANOW,&current),"tcsetattr (current) failed:");
    ERRORCHECK(write(ttyfd,"Hello World\r\n",13),"write failed");
    ERRORCHECK(tcsetattr(ttyfd,TCSADRAIN,&saved),"tcsetattr (saved) failed:");
    ERRORCHECK(close(ttyfd),"close failed");
    exit(0);
}
        

> 

-- 
Robert Heller             -- 978-544-6933
Deepwoods Software        -- Custom Software Services
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Re: [beagleboard] C programing of Uart peripheral in beaglebone black (Linux)

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