January 24, 2026

Allwinner H5 chip - boot -- introduction

This series began while I was working on the H5 network problems. I decided to build U-boot (and ATF) from source, expecting it to be a simple process that would take an hour or two. Several days later, I was still working on it.

It should have been a one hour process. For reasons that are still unclear both the ATF and U-boot binaries compile and link to produce code that is bigger than expected. The ATF code (namely BL31) needs to fit into a specific OCM (on chip memory) area. The limit seems to be 48K or 50K. Read on for all the details.

This has afforded a chance to get into many details of the H5 boot process, as well as U-boot setup itself, which is always an interesting study. At leas I hope you think so if you are reading this.

Have any comments? Questions? Drop me a line!

Tom's electronics pages / tom@mmto.org