+ v1 = test_ym_ab_sync();
+ start = get_line();
+ write8(0xa04001, 0x3f); // clear
+ burn10(3420*11/7/10); // ~11 scanlines
+ v2 = read8(0xa04000);
+ v3 = test_ym_ab_sync2();
+ line_diff = get_line() - start;
+ expect(ok, v1, 3);
+ expect(ok, v2, 0);
+ expect(ok, v3, 3);
+ expect_range(ok, line_diff, 18, 19);