We are using Carambola 2 for internet of things communication hub, and are seeing usb issues with all kind of devices, 3g, flash and bluetooth.

We are moving away from using usb, and will use SDHC cards via SPI protocol. I recommend you do the same.

All kinds of issues... same issues as you had with flash, flash gets unmounted and switches to read-only...
Bluetooth is giving us much more treouble, so much so that not even restarting bluetooth service or unplugging and plugging devices helps, only full reboot fixes issues when bluetooth becomes unresponsive.

We are moving bluetooth to ether UART or SPI. Flash will be definitelly moved to SPI, and RTC clock will be moved to i2c. For i2c and SPI we use GPIO pins and bitbanging.

Search on this and on OpenWrt forum, I saw some people suggest some SPI chips that give you multiple UART's. I would keep away from USB as much as possible, it just have us headaches and weeks of troubleshooting.

Dear kuzmuk and valent,

This is a well known Atheros SOC problem, with no nice solution. Here, at 8devices, we also had a lot of trouble with this issue when developing a WeIO board. We have tried a lot of different ways to fix it, but the only thing that seems to work up to this day is to use Microchip USB2640 hub.

Im a little bit mistrustful with Microchip (SMSC) USB2640, due to the huge problems of SMSC LAN9512 combo chip on RPi-s... In addition, its hard to solder QFN package of these chips at home...

I have positive experience with FE1.1s from Terminus. I had no problems with it connected to AR9331 platform, its available in SOP28 package, needs only a very few external components and can be found on ebay and aliexpress...

I had trouble with several different type of GenesysLogic GL85x family - some of them were stable for days, but on another day, it was unstable... freakish and unrealible with AR9331...

Dear kuzmuk,

I checked the status of WeIO schematics and currently they are not publicly released. However, I can give you UPER1 schematics (see attached pdf), which is an extension board for Carambola 2 development board and from hardware point of view WeIO board is very similar to Carambola 2 + UPER1. Hopefully this helps.