Background Telemetry Channel (BTC) on the BlackFin

1
Background Telemetry Channel (BTC) on the BlackFin

• Presented by Alan Martin
• Winter 2004 - ENCM 515

2
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

3
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

4
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

5
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 youll need and
  define them yourself (this is a waste of time in
  my opinion, since the header file is easy to use)

6
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

7
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

8
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

9
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.

10
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).

11
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
• Dont forget to set the refresh rate and activate
  the Auto Refresh

12
Now are you finished?

• Yes. BTC is now ready to use! Build the
  program, run it, and youll see BTC in action!

13
You lied! This doesnt 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)

14
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

15
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.

16
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.
• Theres no better way to learn than by doing

17
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