Copy miyoo handheld Situ open source system 2.8tft

1. Rendering
2. Undetermined issues
    1. The power amplifier circuit has not been verified. The circuit is simple and connected according to the manual, but I don't have a speaker.
    2. There is a problem with the battery power detection, which does not affect the use, and I didn't check it.
    3. The charging current limit is adjusted according to the battery. The current one is a bit slow, and it takes about 3 hours to fully charge. The battery is 1500ma.
3. Hardware differences from the original version
   1. Two of the axby are swapped, and the upper and lower two are in the PCB.
   2. The LR on the back is swapped.
   I didn't pay attention when laying out. I swapped the pins when compiling the kernel, which did not affect it.
   Why not make it a horizontal board? Only the vertical board can be 10x10.
   Can the LR on the back be removed? No. There are 4 function pages that need to be switched through LR, and the direction keys can only be cut in the function page. In addition, the feel of the back panel has increased a lot, and only one motherboard is too thin, which is uncomfortable to hold.
4. Software changes
   1. In order to prevent accidental deletion, Situ wrote uboot and kernel in the TF card boot area. I put uboot, kernel, and device tree in flash.
   2. Adapt key pins.
 
5. Refer to
   Steward-fu website https://steward-fu.github.io/website/handheld.htm
   Yun Ge website https://whycan.com/