Hi~
Our project has an RS232 TXD signal glitch issue when the system shuts down. We fear it will cause some machines abnormal. This glitch was caused by power_en and com_tx(from Xavier SOM UART tx source) active low at the same time. Since we use the power_en pin to turn off the RS232 transceiver, If the power_en pin and com_tx are active low at the same time, this glitch will appear. Is it possible to delay the com_tx signal activating low after the power_en signal is active low ??
Hi~
No, Because Xavier’s dev kit doesn’t have an RS232 transceiver circuit. Is it possible to control UART TX signal timing during system shut down?
We’re thinking of another solution. We’re thinking maybe we can design a GPIO pin to control turning off the RS232 transceiver before the system goes restart, suspend, and all of shut down case(HW shutdown/SW shutdown/Thermal shutdown). Is it possible to do that?
GPIO function step:
system ready to restart, suspend, or shutdown.
GPIO turn off RS232 transceiver before system do restart, suspend or shutdown process
system start system do restart, suspend or shutdown process
Hi, if you can’t observe same glitch on devkit, then it means the glitch is related to your RS232 transceiver only. I am not sure why this glitch (Tx is an output from Xavier) happen, maybe you should find out the source of it first. Or you can try not to use power_en for to turn off transceiver? Or as you said, you can use GPIO to turn off transceiver before system shutdown.
Hi~Trumany,
Do you mean SHUTDOWN_REQ* & SYS_RESET* cannot be programmable by any driver, because it is a hardware logic circuit??
If we want to use a GPIO pin to turn off the transceiver, this GPIO needs to know what time the system will enter the shutdown process and turn off the transceiver before the system enters the shutdown process. Do you know how to select a GPIO that can do this action?
Source of SHUTDOWN_REQ:
Software shutdown(by shutdown in UI or "sudo shutdown now") --> PMIC GPIO5 shutdown then also assert SHUTDOWN_REQ
Thermal overheat shutdown --> T194 SHUTDOWN_N
VDD_IN power bad
SHUTDOWN_REQ assert issue OFF/ON cycle also will trigger SYS_RESET.
However, none of them covers tegra reset case like "sudo reboot". Thus, sw reboot is an exception.
Please take a look and check if you can apply the behavior to your custom board.
Hi~Trumany,
As I mentioned before, This transceiver output glitch is caused by the POWER_EN pin turning off the transceiver and the SOM UART TX signal transitioning low at the same time when the system starts the software shutdown process.
Since we planned to turn off the transceiver before all of our custom board power down, so we chosen the earliest power-down signal in the power sequence (POWER_EN pin). It cannot solve our problem even if we change the SYS_RESET pin to turn off the transceiver. We want to use a GPIO to turn off the transceiver before POWER_EN pin before the system starts the software shutdown process.
Our GPIO function as below step:
PMIC GPIO5 assert ->> our select GPIO turn off this transceiver → SHUTDOWN_REQ# pin assert → POWER_EN pin de-assert -->SYS_RESET# pin assert → turn off all of our custom board power.
Could you let us know which driver controls PMIC GPIO 5?? Our SW engineer needs to know it.
Thanks
Ken
