# Gerrit Niezen

## USB host shield on Espruino: Part 5

I spent a couple of hours this afternoon and again this evening trying to get the TUSB3410 driver to work. I am now able to successfully communicate with the TUSB3410 chip inside the USB cable, set up some configuration parameters and send data to the glucose meter connected to the cable. The final step, actually getting data back from the chip, is still not working.

Basically, I'm getting a 0x0D error back from the USB host controller chip which, according to the data sheet, is a “J-state instead of response” error. What this actually means is not explained anywhere in the documentation, but I did come across a blog post from 2010 that indicates it may be an issue with my “Set Configuration” control transfer message.

Part of my debugging process involved actually using the WebUSB driver I wrote inside the browser and then using Wireshark to sniff the USB packets on the bus. This way I was able to make sure that I'm sending the exact same bytes to the USB controller chip. However, on Linux and macOS it wasn't necessary to set the configuration, so I'm not sure why it's different now.

As a quick aside: To connect to the TUSB3410 chip via WebUSB on Linux, I first had to disable the built-in TUSB3410 kernel driver that claims the device when it's plugged in. To do this, you can type lsmod | grep 3410 to find the name of the kernel driver. On my machine it's ti_usb_3410_5052. To disable it, type sudo modprobe -r ti_usb_3410_5052. To re-enable it, type sudo modprobe ti_usb_3410_5052.