title: ARMv8 backward compatibility with ARMv7 (Snapdragon 820 vs Cortex-A15)
body: <p>I see that ARMv8 is merely an extension of ARMv7 architecture and all code compiled on ARMv7 should run on ARMv8. I am interested in the backward compatibility of ARMv8 to ARMv7. Will code that was compiled on ARMv8 run on ARMv7?</p>
  
  <p>I have a particular exact case of interest: I would like to run the <a href="https://github.com/commaai/openpilot/blob/master/selfdrive/visiond/visiond" rel="nofollow noreferrer">comma.ai's Openpilot visiond binary</a> which was compiled for the <a href="http://www.gsmarena.com/oneplus_3-7995.php" rel="nofollow noreferrer">OnePlus 3 smartphone</a> (Qualcomm MSM8996 Snapdragon 820 CPU) on the <a href="http://elinux.org/Jetson_TK1" rel="nofollow noreferrer">Nvidia Jetson TK1</a> (NVIDIA Cortex-A15 CPU). Will the visiond run on Jetson?</p>
  
  <p>EDIT: There may be more in question than CPU compatibility since visiond probably heavily uses GPU on that phone. Will probably depend whether they use some standard parallelization ways (OpenCL, NEON etc.) or have some custom code for Snapdragons GPU. Even with OpenCL the chance of compatibility is probably quite low on different HW.</p>