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c_demo — Complex Calibration Objects and Async Access

Shows more complex data objects (structs, arrays) and calibration objects (axes, maps and curves). Demonstrates asynchronous polling access to stack variables, consistent atomic parameter updates, and calibration page switching.

What it demonstrates

Feature How it is demonstrated
Maps, curves, lookup tables Calibration parameters with fixed and shared axes
Struct and array measurement Global and stack variables of structured types
Asynchronous stack polling CANape reads counter on the stack via polling (no DAQ event)
Consistent atomic update test_byte1 and test_byte2 updated atomically via indirect calibration mode
Calibration page switching Switch between default and RAM calibration page at runtime
EPK version check Version string verified by CANape on connect
Minimum cycle time benchmark delay_us calibration parameter controls main loop sleep

Files

File Purpose
src/main.c Demo application — calibration objects, async polling, event loop
CANape/ CANape project (A2L auto-upload, XCP UDP, port 5555, indirect cal mode)

Building

./build.sh examples
./build/c_demo

Or with CMake directly:

cmake -B build -S . -DXCPLITE_BUILD_EXAMPLES=ON -DCMAKE_BUILD_TYPE=Debug
cmake --build build --target c_demo
./build/c_demo

Note: This example enables log level 4 (OPTION_LOG_LEVEL 4) so XCP commands are visible on the console — useful for understanding how async access and consistent updates work.

CANape

Open CANape/CANape.ini in CANape. The project is pre-configured for XCP on UDP, port 5555, with automatic A2L upload and indirect calibration mode enabled.

If CANape cannot connect, verify the IP address in Device Configuration / Devices / XCP / Protocol / Transport Layer.

Key concepts

Asynchronous access to stack variable

counter lives on the stack. CANape is configured to poll it once per second (Polling every second measurement mode) — CANape actively reads the value during its lifetime rather than waiting for a DAQ trigger event. The variable also has write access and can be modified from the calibration window.

Consistent parameter changes

test_byte1 and test_byte2 are in the same calibration segment. The application asserts test_byte1 == -test_byte2 and prints a warning if they are ever inconsistent. The indirect calibration mode (enabled in the CANape toolbar) ensures both values are applied atomically — the application never sees a partial update.

Minimum cycle time

The delay_us calibration parameter controls the main loop sleep time. Reducing it probes the minimum measurement cycle time the system can sustain without queue overruns. XCPlite's lock-free queue allows sub-10 µs cycles on typical Linux/macOS hardware.

Example lock-time statistics at 2 µs sleep time (MacBook Pro M3):

Producer acquire lock time statistics:
  count=3032642  max_spins=0  max=29250ns  avg=27ns

Lock time histogram (3032642 events):
  Range                      Count        %  Bar
  --------------------  ----------  -------  ------------------------------
  0-40ns                   1233151   40.66%  #####################
  40-80ns                  1682263   55.47%  ##############################
  80-120ns                   89802    2.96%  #
  ...