Antminer S9 board - rebuild U-boot

I also tried building the Xilinx fsbl (first stage boot loader) from source, and likewise was frustrated working with it. The only thing I have on an SD card that does boot is from a rescue/update image provided by the Antminer people. I can put that onto an SD card and it does run.

One question, not yet answered, is how the Xilinx fsbl and the U-boot spl are related to each other. They both are described to serve the same purpose. Why do we have both of them and what are the differences?

I spent some time writing my own "from scratch" experiment. I coded up the simplest possible thing I could think of, and also coded up a utility to generate a bootrom header and include the binary for my simple image. I was able to get that to work, so this serves as another reference point.

• Rebuild U-boot from source
• Study the SPL build
• Further examination of the SPL
• examination of BOOT.BIN

• Going deeper with JTAG

• Find main and follow execution

Forget all of this and go with Plan B

• Select a plan B
• Try my 2020 sources -- they just work!
• plan B env settings
• plan B hack env variable source
• plan B watchdog
• plan B NAND

• NAND hardware on the Antminer S9
• U-boot shows us the clocks!