for(;;) {
    while(!(TIFR1 & _BV(TOV1)));               // Wait for Timer1 overflow
    TIFR1 |= _BV(TOV1);                        // Clear overflow bit

    show();                                    // Display current line
    if(stopFlag) break;                        // Break when done

    if(++block >= nBlocks) {                   // Past last block?
      if(digitalRead(TRIGGER) == HIGH) {       // Trigger released?
        memset(sdBuf, 0, N_LEDS * 3);          // LEDs off on next pass
        stopFlag = true;                       // Stop playback on next pass
        continue;
      }                                        // Else trigger still held
      block = 0;                               // Loop back to start
    }
    card.readBlock(block + firstBlock, sdBuf); // Load next pixel row
  }