imx-uart RX FIFO overrun when not connected

[stasgil]

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

[igorpadykov]

Hi Stas

with UART1 disconnected, floating long uart board trace can catch noise and

cause overruns. One can check signal with oscilloscope and set appropriate

pull setting in uart Pad Control Register IOMUXC_SW_PAD_CTL_PAD_x_y register.

Also one can try linux from nxp source.codeaurora.org/external/imx repository

linux-imx - i.MX Linux kernel 

Best regards
igor
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