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+--- Thread: baremetal via Zig on PinePhone - JumpDrive help please (/showthread.php?tid=19882)
baremetal via Zig on PinePhone - JumpDrive help please - WhiteHexagon - 07-01-2025
background: 2 years ago, I was following along with @lupyuen great series of articles to get LVGL running on PinePhone. I was emulating the same journey but using Zig for all the hardware interfacing (and I got quite far). But at the time I was stuck on an old version of Zig and lost motivation. Now I finally have some hardware to run latest Zig, and I decided to port my project over to Zig 0.14 including it's new build system.
I've struggled for a few days to recreate the environment I had running (I also switched from macos to to Linux and still learning!). So I decided to go back to basics, and try to understand how NuttX interects with the JumpDrive image.
This is what I tried:
1. compiling some very simple Zig code, that should toggle the phone LEDs.
2. build the above as an elf file for arm freestanding with a target of cortex_a53
3. created a simple .ld linker file that ensure my entry point is at 0x40080000
4. using objCopy extract hex via the -O binary
5. gzip the resulting binary file into Image.gz
I was expecting that whatever the JumpDrive util does, it somehow jumps to executing the code directly from Image.gz. However now I suspect that this .gz might be a bit more complicated than straight arm machine code. But I have no idea what? and I struggle to follow the NuttX build (maybe something to do with a util called binfmt? but also I saw mention of nxflat).
Ultimately it would be nice to find a way to deploy to PinePhone as 'baremetal'. But for now the JumpDrive 'hack' would be enough, allowing me to hop between SDCards to compare/debug different images.
Does anyone have any idea how to wrap my baremetal code into something JumpDrive can recognize from the Image.gz file please.
RE: baremetal via Zig on PinePhone - JumpDrive help please - WhiteHexagon - 07-07-2025
Finally, booting Zig code 'baremetal' (via JumpDrive trick used by Nuttx)
The Image file is the simple objCopy binary output from the elf file. To get my Zig code to run I had to link it with a bit of assembly code for setting up the arm chips. Actually just the MZ ... ARM 'header' magic number bytes seem to be enough at the moment. Probably the boot loader already did all the hard work