Input overrun(s) on /dev/ttyS0

Everything was ready to move the unit to the final location when I thought I would check the logs…

The system works fine when using the stock SD card.

When using an SSD connected via a USB port for data storage I get “input overrrun(s)” on /dev/ttyS0 about once per second. Clearly I will be losing data - not good!

Looking at the disk activity it looks like the disk writes over the USB link are the only real disk activity. There are few reads and no swap at all. The CPU is not too busy either.

The serial port /dev/ttyS0 is not the best serial port on the RPi, they save that for Bluetooth evidently, but it does have some issues related to CPU speed.

The configuration is the same for non SSD and SD so the problem is definitely related to the USB/SSD interface.

I will try a USB stick later today to see if this is a USB port issue or something quirky related to the USB/SSD. Clearly there is some waiting or contention going on somewhere.

USB2 speed is probably the limit here at around 35MB/s including SATA conversion time. Roll on USB3 when the RPi4 version of Raspberryshake is ready…

In the meantime, any ideas what could be done other than reverting to the SD card?

Can you send the logs so we can take a look?

The log files are attached.RSH.R6B6E.2019-08-29T23_24_33.logs.tar (9.3 MB)

@dgoadby—to clarify, do you have the OS on an external USB, or do you have an SD reader plugged in via USB for data storage purposes?

The whole OS is on the SSD (via the USB adaptor). The OS boots and runs from the SSD. There is no SD or other storage device plugged in. Apart from these overruns it works really well.

Currently I have reverted to an MLC SD card until I understand a bit more of what is going on.

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