samples: hello_ei: Use EI C linkage

- Edge Impulse C linkage used intead of C++ wrapper.

Jira: NCSDK-36946

Signed-off-by: Bartosz Meus <bartosz.meus@nordicsemi.no>

Author: mbarchie

samples/edge_impulse/hello_ei/CMakeLists.txt

@@ -9,19 +9,18 @@ cmake_minimum_required(VERSION 3.20.0)
 find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
 project(hello_ei)
 
-# Add Edge Impulse library as a separate module
-add_subdirectory(edge_impulse)
-
 # Add application source files
 target_sources(app PRIVATE
   src/main.c
-  src/ei_wrapper.cpp
 )
 
 # Add application include directories
 target_include_directories(app PRIVATE
   src/include
 )
 
+# Add Edge Impulse library as a separate module
+add_subdirectory(edge_impulse)
+
 # Link Edge Impulse library to application
 target_link_libraries(app PRIVATE edge_impulse)

samples/edge_impulse/hello_ei/edge_impulse/CMakeLists.ei.template

@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2020 Nordic Semiconductor ASA
+# Copyright (c) 2026 Nordic Semiconductor ASA
 #
 # SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
 #

samples/edge_impulse/hello_ei/edge_impulse/CMakeLists.txt

@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2020 Nordic Semiconductor ASA
+# Copyright (c) 2026 Nordic Semiconductor ASA
 #
 # SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
 #
@@ -31,7 +31,9 @@ foreach(EI_URI IN LISTS EI_URI_PREPARE_LIST)
   # Remove trailing spaces
   string(STRIP ${EI_URI} EI_URI_STRING)
 
+  # # If URI is NOT a URL (http://, https://, file://), treat it as a local path
   if(NOT ${EI_URI_STRING} MATCHES "^[a-z]+://")
+    # Expand any ${VARIABLES} in the path
     string(CONFIGURE ${EI_URI_STRING} EI_URI_STRING)
     if(NOT IS_ABSOLUTE ${EI_URI_STRING})
       # Using application source directory as base directory for relative path.
@@ -52,6 +54,12 @@ else()
   set(EI_API_KEY_HEADER "")
 endif()
 
+# Enable linkage of Edge Impulse library from C code
+target_compile_definitions(zephyr_interface INTERFACE
+  EI_C_LINKAGE=1
+  EIDSP_SIGNAL_C_FN_POINTER=1
+)
+
 include(ExternalProject)
 ExternalProject_Add(edge_impulse_project
   URL ${EI_URI_LIST}
@@ -136,9 +144,3 @@ target_compile_options(edge_impulse
   INTERFACE -Wno-double-promotion
   INTERFACE -Wno-unused
 )
-
-if(CONFIG_EI_WRAPPER)
-  zephyr_library_named(ei_wrapper)
-  zephyr_library_sources(ei_wrapper.cpp)
-  zephyr_library_link_libraries(edge_impulse)
-endif()

samples/edge_impulse/hello_ei/src/ei_wrapper.cpp

@@ -7,10 +7,9 @@
 #include <zephyr/kernel.h>
 #include <zephyr/logging/log.h>
 
-#include "ei_classifier_types.h"
-#include "model-parameters/model_metadata.h"
+#include "edge-impulse-sdk/dsp/numpy_types.h"
+#include "edge-impulse-sdk/classifier/ei_classifier_types.h"
 
-#include "ei_wrapper.h"
 #include "input_data.h"
 
 #define LOG_MODULE_NAME hello_ei
@@ -28,6 +27,12 @@ static struct {
 
 static size_t inference_cnt;
 
+/* External function declaration needed because the function is declared in
+ * edge-impulse-sdk/classifier/ei_run_classifier.h which includes some
+ * C++ source code files thus cannot be included in this C file.
+ */
+extern EI_IMPULSE_ERROR run_classifier(signal_t *signal, ei_impulse_result_t *result, bool debug);
+
 static void print_inference_result(const ei_impulse_result_t *result, int64_t duration)
 {
 	LOG_INF("=== Inference result ===");
@@ -110,6 +115,17 @@ static int get_samples_from_buffer(size_t offset, size_t length, float *out_ptr)
 	return 0;
 }
 
+static EI_IMPULSE_ERROR run_ei_classification(ei_impulse_result_t *ei_result, size_t window_size)
+{
+	signal_t features_signal = {
+		.get_data = get_samples_from_buffer,
+		.total_length = window_size
+	};
+
+	return run_classifier(&features_signal, ei_result,
+		IS_ENABLED(CONFIG_EI_WRAPPER_DEBUG_MODE));
+}
+
 static int run_model(const float *input_data, size_t input_data_size)
 {
 	__ASSERT_NO_MSG(input_data != NULL);
@@ -118,7 +134,7 @@ static int run_model(const float *input_data, size_t input_data_size)
 	size_t sample_cnt = 0;
 	int64_t start_time, delta;
 	ei_impulse_result_t inference_result;
-	int err;
+	EI_IMPULSE_ERROR err;
 
 	clear_sample_buffer();
 	inference_cnt = 0;
@@ -133,11 +149,11 @@ static int run_model(const float *input_data, size_t input_data_size)
 		 */
 		if (sample_cnt >= EI_CLASSIFIER_DSP_INPUT_FRAME_SIZE) {
 			start_time = k_uptime_get();
-			err = ei_wrapper_run_inference(&inference_result, EI_CLASSIFIER_DSP_INPUT_FRAME_SIZE);
+			err = run_ei_classification(&inference_result, EI_CLASSIFIER_DSP_INPUT_FRAME_SIZE);
 			delta = k_uptime_delta(&start_time);
 
-			if (err != 0) {
-				LOG_ERR("Inference failed with error code: %d", err);
+			if (err != EI_IMPULSE_OK) {
+				LOG_ERR("Classification failed with error code: %d", err);
 				return -1;
 			}
 
@@ -158,8 +174,6 @@ int main(void)
 {
 	print_model_info();
 
-	ei_wrapper_init(&get_samples_from_buffer);
-
 	LOG_INF("Running inference on sine wave input data");
 	LOG_SEPARATOR();