/* Kookabus-01 reader for Linux (Raspberry Pi, Jetson, any board with /dev/i2c-N).
 *
 *   gcc -O2 -o kookabus kookabus.c && ./kookabus /dev/i2c-1 0x40
 *
 * Prints one line a second. Exits non-zero when the pack falls below the cut-off,
 * so a shell loop or systemd unit can stop the load.
 */
#include <fcntl.h>
#include <linux/i2c-dev.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <unistd.h>

#define R_SHUNT  0.005   /* ohm; trim against a multimeter if current reads off */
#define I_LSB    0.0005  /* A per CURRENT bit */
#define CONFIG   0x4527  /* 16-sample average, 1.1 ms conversions, continuous */
#define V_CUTOFF (5 * 3.0)

static int fd;

static void wr(uint8_t reg, uint16_t val)
{
    uint8_t b[3] = { reg, val >> 8, val & 0xFF };
    if (write(fd, b, 3) != 3) { perror("i2c write"); exit(2); }
}

static uint16_t rd(uint8_t reg)
{
    uint8_t b[2];
    if (write(fd, &reg, 1) != 1 || read(fd, b, 2) != 2) { perror("i2c read"); exit(2); }
    return (b[0] << 8) | b[1];
}

int main(int argc, char **argv)
{
    const char *dev = argc > 1 ? argv[1] : "/dev/i2c-1";
    int addr = argc > 2 ? (int)strtol(argv[2], NULL, 0) : 0x40;

    if ((fd = open(dev, O_RDWR)) < 0 || ioctl(fd, I2C_SLAVE, addr) < 0) { perror(dev); return 2; }
    if (rd(0xFE) != 0x5449) { fprintf(stderr, "no INA226 at 0x%02x\n", addr); return 2; }

    wr(0x00, CONFIG);
    wr(0x05, (uint16_t)(0.00512 / (I_LSB * R_SHUNT) + 0.5)); /* 2048 */

    for (;;) {
        double v = rd(0x02) * 0.00125;
        double i = (int16_t)rd(0x04) * I_LSB;
        double p = rd(0x03) * 25 * I_LSB;
        printf("%6.2f V  %6.3f A  %6.1f W\n", v, i, p);
        fflush(stdout);
        if (v < V_CUTOFF) { fprintf(stderr, "pack below %.1f V, stop the load\n", V_CUTOFF); return 1; }
        sleep(1);
    }
}