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What happens when a CPU starts

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Re: What happens when a CPU starts

#121

Post by Dork1234 »

tenebrisalietum wrote: post #106
rmckayfleming wrote: post #102

Earlier quoted context omitted.

A recurring question I have is: how many microcontrollers/CPUs are in a modern personal computer? There are clearly a lot, but just how many?

- the embedded controller (EC) - the CPU core in the chipset that runs the ME/PSP - if the TPM is not an fTPM, it has a CPU I'm sure. - if your NIC has offload engines, it has a CPU or two. - each storage device has a CPU. - each Wi-Fi device has a CPU. - thunderbolt controller takes firmware, it has a CPU. I'd bet USB3 and 4 do too. - any USB device has a CPU on the other end accepting and interpreting commands. - s…

Apple laptop chargers had a 16bit MSP430 microcontroller in them, the same performance as original Macintosh.

Apple Thunderbolt Cables have a ARM chip on each end of the connector.

Every Intel CPU has atleast one smaller x86 core that isn't visible to the user that is running MINIX.This CPU is responsible for MicroCode updates.

Re: What happens when a CPU starts

#122

Post by P_I_Staker »

billti wrote: post #3

Amongst the first sentences... > It may be thought of as what happens when a whole computer starts, since the CPU is the center of the computer and the place where the action begins. I thought that too. Last year I spent a while getting as low-level as I could and trying to understand how to write a boot loader, a kernel, learn about clocks and pins and interrupts, etc. I thought, "I know, I'll get a Raspberry Pi! Th…

This is very common in embedded systems, and honestly I'm not surprised to see this, even with projects like Raspberry Pi... although, I do think it's a big shortcoming for a project like that.

In a "real project" you would be relying on your suppliers and other teams / colleagues for many of the "hard questions". Chances are you'd have a contact with the silica manufacturer, just as a major example.

There would be a boot team, or sometimes just one boot developer. If anything goes wrong, or you want to change anything, you would be pretty helpless without them. You can go to the various specs and code, but this can be quite in depth if you're starting from scratch.

Change project or micro? Chances are that all goes out the window, and you have to start from scratch.

Re: What happens when a CPU starts

#123

Post by storklathe »

fennecfoxy wrote: post #108
storklathe wrote: post #105

Could anybody clarify for me the purpose of the NOP opcode that the article refers to? I would think that something like a "do nothing" instruction would want to be optimized away as much as possible, but maybe there's some hidden facet of the instruction protocol I'm not familiar with that necessitates it?

I don't know how much it's really used these days, but when I've done asm stuff before if you have tight timing requirements in assembly, say you're bit banging an IO for some arcane serial protocol a la WS281X LED series, where it doesn't use a hardware supported serial protocol like SPI (where you can just DMA what you want to send to the controller) you then have to implement this protocol manually, in code, switc…

Thank you so much, that makes perfect sense!

Re: What happens when a CPU starts

#124

Post by Agingcoder »

markus_zhang wrote: post #45
tmtvl wrote: post #37

Earlier quoted context omitted.

writing programs for old game consoles, Oh yeah, like the Intellivision. particularly the Nintendo DS. Oh come on, the DS ain't that old.

Never done anything but I think the gameboy family is a good choice. Unlike NES or SNES which use assembly heavily, we can use C for the GBA. There are also great communities devoted for them.

The nes is a simple but extremely elegant machine. Assembly isn't a problem, since the cpu is very simple, I recommend playing with it.

Re: What happens when a CPU starts

#125

Post by DonHopkins »

MuffinFlavored wrote: post #44
toast0 wrote: post #40

Earlier quoted context omitted.

I dunno about the DS, which doesn't really qualify as that old to me; it's got a pretty decent sized rom for when you don't have a cartridge in, and I'd guess the SDK gives you something approaching an OS, maybe even with a threading library. But on real old hardware, you're not going to run threads or a scheduler, you're going to run one iteration of your game loop, then wait for a sign that it's time to do your gra…

> In a typical Windows 10 installation with many background processes and services, the CPU context switching rate can vary greatly depending on the specific system's hardware configuration, running processes, and workload. However, on a typical system, the context switching rate can be anywhere from a few hundred to a few thousand times per second. Would you agree with this statement from ChatGPT? Is the Windows ker…

Please stop using ChatGPT to write your comments. Nobody here is here to have a conversation with ChatGPT, and anyone who wants to talk with ChatGPT instead of actual human beings can do that privately without polluting the conversations of real human beings.

Re: What happens when a CPU starts

#126

Post by markus_zhang »

Agingcoder wrote: post #124
markus_zhang wrote: post #45

Earlier quoted context omitted.

Never done anything but I think the gameboy family is a good choice. Unlike NES or SNES which use assembly heavily, we can use C for the GBA. There are also great communities devoted for them.

The nes is a simple but extremely elegant machine. Assembly isn't a problem, since the cpu is very simple, I recommend playing with it.

Definitely. I guess one can climb the ladder by first programming the NES and then SNES and just go up, maybe even learn some Japanese to immerse in the life of a Japanese game developer in the 80s/90s. Could be a long but interesting side project.

Re: What happens when a CPU starts

#127

Post by pabs3 »

billti wrote: post #3

Amongst the first sentences... > It may be thought of as what happens when a whole computer starts, since the CPU is the center of the computer and the place where the action begins. I thought that too. Last year I spent a while getting as low-level as I could and trying to understand how to write a boot loader, a kernel, learn about clocks and pins and interrupts, etc. I thought, "I know, I'll get a Raspberry Pi! Th…

This keynote about hardware vs operating systems knowledge of hardware was enlightening:

https://www.youtube.com/watch?v=36myc8wQhLo

Re: What happens when a CPU starts

#128

Post by pabs3 »

billti wrote: post #3

Amongst the first sentences... > It may be thought of as what happens when a whole computer starts, since the CPU is the center of the computer and the place where the action begins. I thought that too. Last year I spent a while getting as low-level as I could and trying to understand how to write a boot loader, a kernel, learn about clocks and pins and interrupts, etc. I thought, "I know, I'll get a Raspberry Pi! Th…

Check out the LibreRPi project, they are aiming to reverse engineer, document and replace the GPU firmware boot blob and other blobs.

https://github.com/librerpi/

Re: What happens when a CPU starts

#129

Post by MichaelZuo »

monocasa wrote: post #18
pclmulqdq wrote: post #2

"It starts at 0 and executes instructions" is a funny, but mostly true way to express this. Some people are shocked that no magic happens before the instructions start.

Sort of. It's actually fairly common on larger cores (and particular, larger SoCs) for there to exist magic that happens before architectural reset vectors. https://www.bunniestudios.com/blog/?p=5127 > By pre-boot code, I’m not talking about the little ROM blob that gets run after reset to set up your peripherals so you can pull your bootloader from SD card or SSD. That part was a no-brainer to share. I’m talking abo…

So what boots the ‘pre-boot’ code?

Re: What happens when a CPU starts

#130

Post by P_I_Staker »

monocasa wrote: post #18
pclmulqdq wrote: post #2

"It starts at 0 and executes instructions" is a funny, but mostly true way to express this. Some people are shocked that no magic happens before the instructions start.

Sort of. It's actually fairly common on larger cores (and particular, larger SoCs) for there to exist magic that happens before architectural reset vectors. https://www.bunniestudios.com/blog/?p=5127 > By pre-boot code, I’m not talking about the little ROM blob that gets run after reset to set up your peripherals so you can pull your bootloader from SD card or SSD. That part was a no-brainer to share. I’m talking abo…

Yeah, I was actually thinking the basic behavior that OP mentioned could be quite rare these days. Last project I worked on there was a whole startup procedure. You could even use a special bootloader that they kept in ROM, if you wanted... It did a number of other things that were generally not visible to the developer, but probably required some CPU interaction.
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