tiva-daq

This is a work-in-progress implementation of a USB data acquisition system using either the Texas Instruments Stellaris LM4F120 or Tiva TM4C123G low-cost ARM Cortex-M4 development board.

Note

Note on Stellaris vs. Tiva: The Stellaris LM4F120 LaunchPad is obsolete and has been replaced by the Tiva TM4C123G LaunchPad. They are very similar and I am actually using a Stellaris board I've had lying around for a few years even though I'm using the Tiva libraries.

Building

I got TI's Tiva libraries from here: https://github.com/yuvadm/tiva-c. I put the whole thing at ~/ti/tivaware. Then I installed arm-none-eabi-gcc using my OS package manager.

The code here started out from usb_dev_bulk example from tivaware/boards/ek-tm4c123gxl/.

Assuming you've done all the above, you should be able to build the binary with just:

$ make

Flashing

I installed the lm4flash tool from here: https://github.com/utzig/lm4tools.

To be able to access the ICDI USB port as a non-root user (and looking ahead to be able to access the primary microcontroller's USB port), I installed the following udev rules to /etc/udev/rules.d/71-ti-permissions.rules:

# rule for the ICDI USB
SUBSYSTEM=="usb", ATTRS{idVendor}=="1cbe", ATTRS{idProduct}=="00fd", MODE:="0666"
# rule for primary microcontroller USB peripheral
SUBSYSTEM=="usb", ATTRS{idVendor}=="1cbe", ATTRS{idProduct}=="0003", MODE:="0666"

Then I added a rule to the Makefile to load the program onto the board:

$ make flash

Testing

Currently, the application prints some debug information to the microcontroller's UART0 which routes through the board's second microcontroller to the ICDI USB port. You can use screen to monitor that:

$ screen /dev/ACM0 115200

More importantly, the point of the whole thing is to stream data over the primary microcontroller's USB peripheral. To test the functionality and easily update the test script as new features are developed, I'm using Python with the pyusb library. I like to do everything in Python in a virtual environment:

$ python -m venv .venv
$ source .venv/bin/activate{.your-shell}
(.venv) $ pip install pyusb numpy

pyusb is really just a wrapper around a USB library (it supports several), so you'll need a backend installed. I have libusb-1.x installed.

Now you can run the test script:

(.venv) $ python test.py

TODO

• Use a control transfer to send a "start" command from the host (laptop)
• Start a timer to periodically write data from the device
• Enable an ADC channel to actually sample some data
• Get some kind of turnkey SPI sensor and start collecting data from it