Sergey Zapunidi

It is possible to boot from eMMC, where its bootloader checks SD card for boot sector and boots from it if the test is positive. I believe that is how I booted from SD the first time, having Firefly official Lubuntu installed on eMMC. I wonder why Armbian do not use this way? Space bar didn't work for me. I tried pressing space bar at the moment of the attached screenshot, few lines before, on the appearance of the first line, before that, seconds after that, but it all didn't disturb the booting sequence in any way. I solved my initial problem with Rockchip AndroidTool software. Firefly has "Recovery" button that you press and hold before power up. It brings the board into MaskROM mode. Then you can install one of the official Ubuntu/Android images on eMMC and get booting from SD back. I had to change several USB-C cables and USB ports on PC, until it worked. Use short cable, connect closer to the USB host IC on the PC motherboard. Otherwise USB device is recognized and MaskROM status is displayed, but writing bootloader fails with no explanation. All software is downloadable from here: http://en.t-firefly.com/doc/download/3.html. Flashing instructions are here: http://wiki.t-firefly.com/en/Firefly-RK3399/flash-image.html#connect-device Thank you for this suggestion. I may try it in the future. But it troubles me that EMMC_CLK (TP31) is directly connected to the RK3399 chip which drives it (see attached schematics). If I short circuit TP31 to TP32 (GND) then I short circuit push/pull output, which is usually risky. In my practice from the MCU world, continuous short circuit of TTL output pin usually leads to pin damage. Nevertheless I found that short circuiting TP31 and TP32 is in the official Firefly documentation: http://wiki.t-firefly.com/en/Firefly-RK3399/maskrom.html

I have Firefly RK3399 board. I ran armbian from SD card successfully the first time. After full init, I ran nand-sata-flash.sh install script, also successfully. But then I can't boot from the same SD card anymore. I always boot from the eMMC memory. I expected that boot sequence would be set on SD card first, then check eMMC.