no data being piped thru /run/mpa/tflite_data

ssansoy

i wrote a small c program to extract object detection data from /run/mpa/tflite_data

when I list the contents of tflite_data i get two files: info & request.

when i "cat /run/mpa/tflite_data/info" i get the the correct data type of ai_detection_t

when i "cat /run/mpa/tflite_data/request" the system just hangs as if waiting for data

I know data is being sent as the tflite camera is showing object detections in the web interface

here is my simple c program

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <stdint.h>
#include <sys/types.h>
#include <sys/stat.h>

#define BUF_LEN 32
#define MAX_DETECTIONS 100
#define PIPE_PATH "/run/mpa/tflite_data/request"

typedef struct ai_detection_t {
uint32_t magic_number;
int64_t timestamp_ns;
uint32_t class_id;
int32_t frame_id;
char class_name[BUF_LEN];
char cam[BUF_LEN];
float class_confidence;
float detection_confidence;
float x_min;
float y_min;
float x_max;
float y_max;
} attribute((packed)) ai_detection_t;

int open_pipe(const char* path) {
int fd = open(path, O_RDONLY);
if (fd < 0) {
perror("Failed to open pipe");
exit(EXIT_FAILURE);
}
return fd;
}

ssize_t read_pipe(int fd, void* buffer, size_t size) {
return read(fd, buffer, size);
}

int main() {
int pipe_fd = open_pipe(PIPE_PATH);

ai_detection_t detections[MAX_DETECTIONS];
ssize_t bytes_read;

while (1) {
    bytes_read = read_pipe(pipe_fd, detections, sizeof(detections));
    if (bytes_read <= 0) {
        usleep(10000);
        continue;
    }

    int num_detections = bytes_read / sizeof(ai_detection_t);

    printf("\nReceived %d detections:\n", num_detections);

    for (int i = 0; i < num_detections; ++i) {
        ai_detection_t *det = &detections[i];
        printf("Detection %d:\n", i + 1);
        printf("  Magic Number:        0x%X\n", det->magic_number);
        printf("  Timestamp (ns):       %ld\n", det->timestamp_ns);
        printf("  Frame ID:             %d\n", det->frame_id);
        printf("  Class ID:             %u\n", det->class_id);
        printf("  Class Name:           %s\n", det->class_name);
        printf("  Camera Name:          %s\n", det->cam);
        printf("  Class Confidence:     %.2f\n", det->class_confidence);
        printf("  Detection Confidence: %.2f\n", det->detection_confidence);
        printf("  Bounding Box (x_min,y_min,x_max,y_max): (%.2f, %.2f, %.2f, %.2f)\n",
               det->x_min, det->y_min, det->x_max, det->y_max);
    }

    usleep(10000);
}

close(pipe_fd);
return 0;

}

The code just hangs waiting for data to come in from the pipe /run/mpa/tflite_data/request

what am i doing wrong?

Alex Kushleyev

@ssansoy , you cannot access the data from these pipes directly, you have to use the MPA mechanisms to do that. There is an example of doing that for tflite detections right here : https://gitlab.com/voxl-public/voxl-sdk/utilities/voxl-mpa-tools/-/blob/master/tools/voxl-inspect-detections.c and the compiled app should also be present in the SDK, so you can run it on your VOXL2 (voxl-inspect-detections).

Alex