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imx6sx UART4 not working

Question asked by DaeYun Han on Feb 21, 2017
Latest reply on Feb 22, 2017 by igorpadykov



1. under i.mx6sx board, uart4 has been setup as follows, and, "/dev/ttymxc3" was registered as kernel device.

but when opening the device as uart device, suddenly system crashed without any error(for example, segmentation fault). other uart devices are working well, /dev/ttymxc0, /dev/ttymxc1,/dev/ttymxc2, /dev/ttymxc4,/dev/ttymxc5

why ttymxc3 is making noise during open serial?


static int open_serial( char *dev_name, int baud, int vtime, int vmin )
struct termios newtio;

// trying to open fail
printf("\nuart port: %s\n",dev_name);


fd = open( dev_name, O_RDWR| O_NOCTTY /*| O_NDELAY |O_SYNC | O_NONBLOCK*/);



if ( fd < 0 )
// file open failed
printf( "Device OPEN FAIL %s\n", dev_name );
return -1;


2. imx6sx-sdb.dts has uart pin assigned at CSI_PIXCLK, CSI_MCLK

To prevent CSI pin mux functions from overlapping other pins, all related CSI pins has been reviewed again and other already-assigned uart4 pin has been checked again. but this is only separate pin muxing.

I've checked again if uart4 tx, rx pin would work well in terms of hw circuit. each pin has been configured as gpio output, and the gpio output test was okay. this pin should not assigned as UART4 pin? otherwise, is there solution for workaround in this case?


&uart4 {
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_uart_4>;
status = "okay";


pinctrl_uart_4: uart4grp {
fsl,pins = <


Thanks and Regards,