I wonder if learning how a more simple microcontroller boots might help you.
I had the same questions as you around a year ago. As other commenters mentioned, modern hardware is incredibly complex and needs to go through many, many steps before it can boot a kernel. Modern CPUs have a bunch of legacy requirements that still exist to keep backward compatibility with older hardware.
One good example of these legacy requirements is the A20 line on x86 [1]. A20 can be considered a boolean flag that determines whether the CPU can access more than 1MB of RAM. The A20 flag was introduced in the Intel 286 because its predecessor, the 8086 had a limit of 1MB of RAM. The 286 needed to access 16MB of RAM, so Intel introduced the A20 flag that determines whether the CPU can access memory past 1MB. The A20 line still exists in x86_64 CPUs today, so it needs to be enabled before the entire RAM address space is used.
There are a TON of legacy requirements like the A20 line on modern CPUs (especially x86_64). It can make it very difficult to figure out what is going on in the boot process. For me, I found it much easier to start learning how simple pieces of hardware works before moving on to x86. The boot process for Raspberry Pi's RP2040 microcontroller is explained in the datasheet [2] and I found it to be a great resource to figure out which hardware needs to be initialized and what that actually means.
Just like x86, microcontrollers have many tasks they need to complete before loading the main program. But these steps are much less ambiguous and are described very well in the RP2040 datasheet. It lists every step that it goes through before the main program starts (including stuff like initializing the clocks to specified speeds). After I felt like I thoroughly understood how the RP2040 boots, it became much easier to understand why the bootloader needs to complete certain tasks.
Not sure if you are familiar with assembly, but you can also checkout part of the RP2040's bootloader here [3]. There are a few different bootloaders for the RP2040, the one I linked is the one referenced in the datasheet. Its purpose is to load the main program from a specified location in the flash memory chip.
Remember that the boot process on x86 processors has been changing for around 40 years, so expect it to take a while before you feel more comfortable with the terms used in bootloading and hardware. I've been learning this stuff for around a year and still feel like I only understand a fraction of the x86 boot process. But I find it so fascinating that I can't help but want to learn more of its complexity.
I love talking about hardware and the boot process, so feel free to let me know if you have any more questions! :)
I had the same questions as you around a year ago. As other commenters mentioned, modern hardware is incredibly complex and needs to go through many, many steps before it can boot a kernel. Modern CPUs have a bunch of legacy requirements that still exist to keep backward compatibility with older hardware.
One good example of these legacy requirements is the A20 line on x86 [1]. A20 can be considered a boolean flag that determines whether the CPU can access more than 1MB of RAM. The A20 flag was introduced in the Intel 286 because its predecessor, the 8086 had a limit of 1MB of RAM. The 286 needed to access 16MB of RAM, so Intel introduced the A20 flag that determines whether the CPU can access memory past 1MB. The A20 line still exists in x86_64 CPUs today, so it needs to be enabled before the entire RAM address space is used.
There are a TON of legacy requirements like the A20 line on modern CPUs (especially x86_64). It can make it very difficult to figure out what is going on in the boot process. For me, I found it much easier to start learning how simple pieces of hardware works before moving on to x86. The boot process for Raspberry Pi's RP2040 microcontroller is explained in the datasheet [2] and I found it to be a great resource to figure out which hardware needs to be initialized and what that actually means.
Just like x86, microcontrollers have many tasks they need to complete before loading the main program. But these steps are much less ambiguous and are described very well in the RP2040 datasheet. It lists every step that it goes through before the main program starts (including stuff like initializing the clocks to specified speeds). After I felt like I thoroughly understood how the RP2040 boots, it became much easier to understand why the bootloader needs to complete certain tasks.
Not sure if you are familiar with assembly, but you can also checkout part of the RP2040's bootloader here [3]. There are a few different bootloaders for the RP2040, the one I linked is the one referenced in the datasheet. Its purpose is to load the main program from a specified location in the flash memory chip.
Remember that the boot process on x86 processors has been changing for around 40 years, so expect it to take a while before you feel more comfortable with the terms used in bootloading and hardware. I've been learning this stuff for around a year and still feel like I only understand a fraction of the x86 boot process. But I find it so fascinating that I can't help but want to learn more of its complexity.
I love talking about hardware and the boot process, so feel free to let me know if you have any more questions! :)
[1] https://en.wikipedia.org/wiki/A20_line
[2] https://datasheets.raspberrypi.com/rp2040/rp2040-datasheet.p...
[3] https://github.com/rp-rs/rp2040-boot2/blob/main/src/boot2_w2...