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imx-uart RX FIFO overrun when not connected

Question asked by Stas Gil on Feb 6, 2019
Latest reply on Feb 6, 2019 by igorpadykov

Hi Community,

 

    We have a custom board based on the sabresd board, with imx6dl processor, using krogoth bsp and kernel 4.1.15

 

    I am observing the following strange behaviour:

 

   Sometimes when i boot the board with UART1 disconnected, and after the boot process is complete, i connect the UART to check the logs, i see the following (full log attached):

 

Feb 5 17:26:21 imx6dl-ctems-alpha kernel: sysrq: SysRq : HELP : loglevel(0-9) reboot(b) crash(c) terminate-all-tasks(e) memory-full-oom-kill(f) kill-all-tasks(i) thaw-filesystems(j) sak(k) show-backtrace-all-active-cpus(l) show-memory-usage(m) nice-all-RT-tasks(n) poweroff(o) show-registers(p) show-all-timers(q) unraw(r) sync(s) show-task-states(t) unmount(u) show-blocked-tasks(w)
Feb 5 17:26:21 imx6dl-ctems-alpha kernel: imx-uart 2020000.serial: Rx FIFO overrun
Feb 5 17:26:23 imx6dl-ctems-alpha kernel: sysrq: SysRq : Show Blocked State
Feb 5 17:26:23 imx6dl-ctems-alpha kernel: task PC stack pid father
Feb 5 17:26:23 imx6dl-ctems-alpha kernel: sysrq: SysRq : HELP : loglevel(0-9) reboot(b) crash(c) terminate-all-tasks(e) memory-full-oom-kill(f) kill-all-tasks(i) thaw-filesystems(j) sak(k) show-backtrace-all-active-cpus(l) show-memory-usage(m) nice-all-RT-tasks(n) poweroff(o) show-registers(p) show-all-timers(q) unraw(r) sync(s) show-task-states(t) unmount(u) show-blocked-tasks(w)
Feb 5 17:26:23 imx6dl-ctems-alpha kernel: imx-uart 2020000.serial: Rx FIFO overrun
Feb 5 17:26:23 imx6dl-ctems-alpha kernel: sysrq: SysRq : HELP : loglevel(0-9) reboot(b) crash(c) terminate-all-tasks(e) memory-full-oom-kill(f) kill-all-tasks(i) thaw-filesystems(j) sak(k) show-backtrace-all-active-cpus(l) show-memory-usage(m) nice-all-RT-tasks(n) poweroff(o) show-registers(p) show-all-timers(q) unraw(r) sync(s) show-task-states(t) unmount(u) show-blocked-tasks(w)
Feb 5 17:26:23 imx6dl-ctems-alpha kernel: imx-uart 2020000.serial: Rx FIFO overrun

 

There is some kernel debug stuff i will disable, but i'm not sure if that will help, since this happens intermittently.

The UART configuration is:

115200 8N1, no flow control, connected to imx uart 1. (only TX and RX lines are connected in HW, so HW flow control is not possible.

 

Any ideas ?

 

Thanks

Stas

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