The revised version of the SensorTag is pretty impressive packing a total of 10 sensors in its tiny form factor. The tag also comes with a flash chip for an application developer to store all the data that is collected. Unfortunately, if the flash chip is used, a user can run into an unavoidable debug issue.

First, a few details on the flash. The chip is a Winbond W25X40CLUXIG. It has 4M-bit of flash memory and talks via SPI. TripWire summarizes the issue below:

Here’s a heads-up for anyone that wants to use the external SPI flash memory on the SensorTag: it’s not accessible while a debugger session is active. Unfortunately the pin on the SensorTag’s CC2650 which outputs the SPI clock to the flash memory is also used as the JTAG TDI pin.

This means that if you are designing a project centered around collecting sensor data and storing them for future download, it may be a challenge to develop SPI code to store and retrieve data. It also poses a challenge further down the road while debugging your application and the application needs flash access.

TripWire has done some great research on using the flash chip to store SensorTag data and lists a few dos and don’ts. There is no current fix for this hardware revision of the SensorTag. If there is one, we’ll post up here.

Links

• Warning! JTAG interferes with SensorTag external flash access
• SensorTag-2 homepage.
• Winbond W25X40CLUXIG 4M-bit flash chip.
• CC2650STK tool page.
• Browse other 43oh SensorTag articles.