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Wake-up from suspend by UARTs

Question asked by Engin Lee on May 2, 2019
Latest reply on May 2, 2019 by Engin Lee



I found a strange issue on my i.MX6ULL board:

There is a MCU connect to CPU with UART3, and UART2 is unused.

Application access ttymxc2 without any problem, and also set "enabled" to "/sys/class/tty/ttymxc2/power/wakeup".

But after suspend to RAM (echo mem > /sys/power/state), ttymxc2 becomes abnormal, I cannot read/write anymore.

And I can see the power consumption during suspend mode is higher than it should be, about 10% increase.

I tried lots of settings (BSP/USB/SAI/GPIOs), and finally I found a solution: set "enabled" to "/sys/class/tty/ttymxc1/power/wakeup".

Even through there is no signal connect to UART2, but it just working: ttymxc2 works fine after waking up, and power consumption is normal.

I am not sure the reason why it happened, but I can reproduce this issue on both SDKs (4.14.78_ga_1.0.0 and 4.14.98_ga_2.0.0)