Beaglebone Blue UART0 - UART2 exhibit different behavior - UART0 will fault

[Michael Axelrad]

UART 0 & UART 2 Behave Differently

Beaglebone Blue - with a recent recommended Debian release

Below is Strawson's example UART loopback program. With minor changes to read continuously.

I have attached an Arduino 115200 baud char output stream to both the UART0 & UART2 in parallel.

If UART2 is selected the stream will read as expected - maybe forever.

If UART0 is selected the stream will read for perhaps 30 seconds.  The PUTTY cursor will flash and the program stalls until interrupted with a ctl C.

I suspect there is some conflict within LINUX??  If anyone has an idea about this,

it will be greatly appreciated.

/**

 * @file rc_uart_loopback.c

 * @example    rc_uart_loopback

 *

 * This is a test to check read and write operation of UART buses. For this

 * example to work, connect the RX and TX wires of one of the included 4-pin

 * JST-SH pigtails and plug into the UART1 or UART5 headers. You may also elect

 * to test UART0 on the debug header or UART2 on the GPS header. The test

 * strings this programs transmits will then loopback to the RX channel.

 */

#include <stdio.h>

#include <stdlib.h> // for atoi

#include <string.h>

#include <rc/uart.h>

#define BUF_SIZE 32

#define TIMEOUT_S 0.5

#define BAUDRATE 115200

static void __print_usage(void)

{

printf("\n");

printf("Usage: rc_uart_loopback {bus}\n");

printf("This sends a short message out the specified bus and then\n");

printf("reads it back in. This requires connecting RX to TX to make a loopback.\n");

printf("For Robotics Cape or BeagleBone Blue specify bus 0,1,2 or 5\n");

printf("\n");

return;

}

int main(int argc, char *argv[])

{

char* test_str = "Hello World";

int bytes = 10;  //strlen(test_str); // get number of bytes in test string

uint8_t buf[BUF_SIZE];

int ret; // return value

int bus; // which bus to use

// Parse arguments

if(argc!=2){ //argc==2 actually means one argument given

__print_usage();

return -1;

}

else bus = atoi(argv[1]);

if(!(bus==0||bus==1||bus==2||bus==5)){

__print_usage();

return -1;

}

printf("\ntesting UART bus %d\n\n", bus);

// disable canonical (0), 1 stop bit (1), disable parity (0)

if(rc_uart_init(bus, BAUDRATE, TIMEOUT_S, 0,1,0)){

printf("Failed to rc_uart_init%d\n", bus);

return -1;

}

// Flush and Write

printf("Sending  %d bytes: %s \n", bytes, test_str);

rc_uart_flush(bus);

rc_uart_write(bus, (uint8_t*)test_str, bytes);

//repeated reads fom a character stream sent from Arduino at 115200

while(1){

// Read

//printf("reading bytes:\n");

memset(buf,0,sizeof(buf));

ret = rc_uart_read_bytes(bus, buf, bytes);

if(ret<0) fprintf(stderr,"Error reading bus\n");

else if(ret==0) printf("timeout reached, %d bytes read\n", ret);

else printf("Received %d bytes: %s ", ret, buf);

rc_uart_flush(bus);

fflush(stdout);

}

// now write again

printf("\n");

printf("Sending  %d bytes: %s \n", bytes, test_str);

rc_uart_write(bus, (uint8_t*)test_str, bytes);

// read back as line

printf("reading line:\n");

memset(buf,0,sizeof(buf));

ret = rc_uart_read_line(bus, buf, sizeof(buf));

if(ret<0) fprintf(stderr,"Error reading bus\n");

else if(ret==0) printf("timeout reached, %d bytes read\n", ret);

else printf("Received %d bytes: %s \n", ret, buf);

// close

rc_uart_close(bus);

return 0;

}