ADALM-Pluto non-cyclic continues transmit

I am attempting to transmit internally generated signal via the AD9361. Software runs on target (Adalm-pluto).

The samples are generated for 20mS transmission. The time is measured

and takes about 8mS (7869498ns - 8049387ns)

To minimize process time I am using the buffer created by iio_device_create_buffer() to store the

generated samples.

There is always '1' in Status register   iio_device_reg_read(tx, 0x80000088, &val);

The same code is running on host computer without any problems.

What I'm doing wrong?

Thanks.

while(!Stop)

{

...

initialization

....

    tx_buffer = iio_device_create_buffer(tx, iq_buff_size, false);

    if (!tx_buffer) {
        perror("Could not create TX buffer");
        stop();
    }

    char *ptx_buffer = (char *)iio_buffer_start(tx_buffer);
    mybuff = (const uint16_t**)ptx_buffer;

....

printf ("iio_buffer_set_blocking_mode = %d\n",iio_buffer_set_blocking_mode(tx_buffer, true));

.......

            clock_gettime(CLOCK_MONOTONIC_RAW, &tpStart);

               ......

               sample generation code

               ......

            clock_gettime(CLOCK_MONOTONIC_RAW, &tpEnd);
            timeDelta = tpEnd.tv_nsec - tpStart.tv_nsec;
            if(timeDelta < 0)
            {
                timeDelta += 1000000000;
            }

           bytesTramsmitted = iio_buffer_push(tx_buffer);

           iio_device_reg_read(tx, 0x80000088, &val);
           if(val == 1)
           {
//            printf("Sratus register %d Time delta =  %ld\n",val, timeDelta);
           }
          if(val)
          {
               iio_device_reg_write(tx, 0x80000088, val);
          }

}