Press and hold the button (or Home button on some devices).
Theoretically, it is possible to run mainline Linux on the A50, but support is almost nonexistent. The sunxi‑tools project does not yet recognize the A50 chipset, and no device tree has been submitted to the mainline Linux kernel. The A50 remains a “community‑supported only” SoC, and with few devices in the hands of developers, progress is slow. allwinner a50 firmware
The Ultimate Guide to Allwinner A50 Firmware: Updates, Flashing, and Troubleshooting Press and hold the button (or Home button on some devices)