Background Telemetry Channel (BTC) on the BlackFin Presented by Alan Martin Winter ENCM 515

What is it? BTC is a method of communication between an embedded processor (the Blackfin in this case) and the host (your computer). This communication occurs in the background, not interfering with other tasks that the processor may be performing at the time

How does it work? BTC uses shared registers that both the host and target application have read/write access to during program run-time BTC is designed for use over a JTAG connection through an emulator USB works, but to a limited extent

Why do I care? You can view data without having to stop the processor first. You can view data that is constantly changing, and watch it change You can change data values while the program is running, and the program will immediately use these new values without having to recompile

WOW! How do I use it? You need to include a library file with your project – libbtc532.dlb on the Blackfin 533 You should also include btc.h with your project, unless you know all the macros you’ll need and define them yourself (this is a waste of time in my opinion, since the header file is easy to use)

Is that it? Not entirely. You still need to define some BTC channels in your program You also need to initialize BTC Finally, you need to set the priority of BTC

Channels? Like CNN? You need to define a name for each channel (basically a label for some data you will read) You also need to define the starting address and the length of the channel, much like a circular buffer

Initialize? Priority? What? BTC priority is determined by where you put the btc_poll function call. For example: Placing it in a high-priority interrupt effectively makes it high priority Placing it in a low-priority interrupt gives it low priority Placing it in a loop in the main body of the function can have different effects depending on how interrupts on your system work

Are you quite finished? Well… no. BTC is now setup and ready for use, but you have to setup the BTC window in VisualDSP++ to read/write the values. You also need to do a couple things in order to view a plot being updated by BTC as you go.

BTC memory? The BTC memory window is a debug window, much like Plot. It can be accessed through the same menu Double-click on a number to edit it (if possible).

Plot windows with BTC? How? Open a plot window as normal Right click on the window and select Auto Refresh Settings… and then select the settings you need Don’t forget to set the refresh rate and activate the Auto Refresh

Now are you finished? Yes. BTC is now ready to use! Build the program, run it, and you’ll see BTC in action!

You lied! This doesn’t work! The simulator does not currently support BTC Using the USB connection will give you a much more limited amount of BTC. You can still view arrays, but only one plot at a time can be updated. (There may be other limits as well, but those are what I have found)

Are there any examples? There are a few sample programs available that use BTC. Timer run using C code Timer run using Assembly code FFT code, which updates a plot Audio example, where you can modify a value using BTC for volume control

Did you say Assembly code? Yes, I did. BTC can be run in Assembly code as well as C/C++. The code is only slightly more complicated.

Now I can use BTC? Now you can use BTC. For best learning, download one of the examples and run it. The examples come with a readme.txt file that explains how to operate BTC in VisualDSP++. There’s no better way to learn than by doing

Who told you what to say? (aka References) “VisualDSP++ Development Environment for Analog Devices Embedded Processors for Digital Signal Processing”, Analog Devices, 2003 “VisualDSP++ Getting Started Guide for 16-bit Processors”, Analog Devices, n.d. Examples programs of BTC operation from sample programs installed with VDSP 3.5