Hello!
I want to use RS485 through the UART1 from a costum Board. UART1_SIN, UART1_SOUT and UART1_RTS are connected to the RS485 Transceiver. I'm using the QorIQ 1.8 SDK. Receiving data from a PC through RS485 is possible with cat /dev/ttyS0.
For Sending data from my board there has to be a driver to set the RTS-Signal, because Linux thinks ttyS0 is a normal RS232 (correct me if I'm wrong). So I first modified my device tree for the board:
&duart0 {
linux,rs485-enabled-at-boot-time;
rs485-rts-delay = <0 200>;
uart-has-rs485-half-duplex;
rs485-mode = <1>;
status = "okay";
};
then i searched different communities and copied/wrote a little application trying to send data through RS485:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <asm-generic/ioctl.h>
#include <asm-generic/fcntl.h>
#include <errno.h>
#include <termios.h>
#include <linux/serial.h>
#include <asm-generic/ioctls.h>
//Control struct for setting the port in 485 mode
int main(void){
struct serial_rs485 rs485conf;
int rv, i;
char buffer[20];
int fd = open ("/dev/ttyS0", O_RDWR);
if (fd < 0) {
/* Error handling. See errno. */
printf("Error!\n");
return 0;
}
rs485conf.flags |= SER_RS485_ENABLED;
rs485conf.flags |= SER_RS485_RTS_ON_SEND;
rs485conf.delay_rts_before_send = 0;
rv = ioctl(fd,TIOCSRS485, &rs485conf);
if(rv){
printf("rv = %d\n", rv);
perror("unable to set IOCTL:");
}
for (i=0; i<20; i++){
buffer[i] = 'A' + i;
}
for (i=0; i<30;i++){
printf("Writing [%d]\n", i);
write(fd, buffer, 20);
sleep(1);
}
rs485conf.flags &= ~(SER_RS485_RTS_AFTER_SEND);
close(fd);
return 0;
}
when i execute this code after compiling and building, there comes the following message:
"unable to set IOCTL:: Inappropriate ioctl for device"
Does that mean, that the ioctl() does not support TIOCSRS485 and so the RS485 structure, yet? In the serial.h the struct serial_rs485 is already implementet. Do i missed something? I'm confused about the depth RS485 is integrated in the kernel...
What can i do, to get RS485 work?
king regards,
Jan
