Hello,
I have a design with old but cheap Allwinner A20 processor. At the boot time, u-boot keeps rebooting just after reaching the below line (just after DRAM: 1GiB):

    U-Boot SPL 2019.07 (Oct 13 2020 - 17:36:08 +0300)
    DRAM: 1024 MiB
    CPU: 912000000Hz, AXI/AHB/APB: 3/2/2
    Trying to boot from MMC1  

    U-Boot 2019.07 (Oct 13 2020 - 17:36:08 +0300) Allwinner Technology

    CPU:   Allwinner A20 (SUN7I)
    Model: Olimex A20-OLinuXino-LIME2-eMMC
    I2C:   ready
    DRAM:  1 GiB

I even tried ready images from internet, alghtough some did not reboot countinlusly, but they stuck at the same place (line: DRAM:  1 GiB). BTW, in our PCB, we did not use "SD card detect" mechanical pin, so I already changed the U-boot CONFIG_MMC0_CD_PIN="PH1" to ="" before compile (otherwise it stuck in u-boot SPL and even did not go to u-boot). I treid to play with U-boot settings to have debugging message, but nothing changed. Can anyone give a clue? can the problem be a hardware issue? On internet I saw that I should see something like this, after DRAM line:

    .....
    I2C:   ready
    DRAM:  1 GiB
    MMC:   SUNXI SD/MMC: 0
    In:    serial
    ....

Thank you

it is solved. it has been discussed here that this is due to power source problem.