"Bare metal" boot

Shachar

Hello everyone,

I'm trying to do a bare metal minimal boot on the Zero 2 (at least, I think that's what I did):

1. void _start() {
   
2.     static constexpr uint32_t GpioRegisterBase = 0x0300B000;
   
3.     write_register( GpioRegisterBase + 0x4c, 0x1111'1111 );
   
4.     write_register( GpioRegisterBase + 0x58, 0xffff );
   
5. 
   
6.     while(true) {}
   
7. }
   

Copy code

Compiled and verified the binary does what I need (position independent). I then used the mksunxiboot tool from the latest u-boot to get an 8KB image, which I wrote to an SDCard at 8KB offset in. When put in the Zero 2, I expected to see the power and status leds turned on. Instead, I got nothing. Now I don't know whether my code doesn't run, or whether it runs, but isn't turning on the leds for whatever reason.

Can anyone help?

• I know that I'm not initializing the ram or the clocks or, well, anything. My understanding is that it shouldn't matter to such a small program.
• I know u-boot is doing ... something with the "arm trusted firmware". I have it compiled, but I'd rather not have to use it if I can avoid it. For educational reasons, I'd rather be the one who initializes the RAM and the MMU, and the firmware does both if I let it. At least for now, I do not need to run at EL3, so this shouldn't be a blocker.
  

Shachar

I've ruled out "arm trusted firmware" being the cause of the problem. When I take u-boot's pre-trusted image, run mksunxiboot on it, and flash it, I do get boot messages on the serial console. So I'm guessing that my code _is_ running, just not setting the GPIOs correctly.

Shachar

I've finally managed to get it working.

The main failure that was blocking me from seeing results was that the machine boots in 32 bit mode. I copied the "switch to 64 bit" code from u-boot, and could finally see the leds lighting up.

AustinBrayan

Can someone please help me explain all that is in relation to a bare metal boot and what it even means? I first heard about this term on https://www.sjhmalu.com/product/20-series-aluminum-extrusion-profile, but ever since then, I've been left confused in respect of. So I really do want to know more about it.

MarthaThomp

Bare metal boot refers to the process of starting a computer or server directly from its hardware, bypassing any operating system or software layers. This approach is crucial for specific applications that demand optimal performance and control, such as high-frequency trading or scientific simulations. When it comes to bare metal boot solutions, www.yonglongalu.com offers cutting-edge hardware provisioning services, ensuring rapid and efficient deployment of servers.

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