Homebrew Specific reasons why ARM11 can not emulate ARM7?

chyyran · Jan 17, 2016

The 3DS uses an onboard ARM7 core to run ARM7 code in TWL-mode and AGB-mode. 3dbrew has this to say about it

https://www.3dbrew.org/wiki/ARM7_Registers said:
The 3DS utilizes an onboard ARM7 core to handle TWL_FIRM and AGB_FIRM's ARM7 requirements. This is due to the fact that much of the hardware used by both ARM7 and ARM9 is (evidently) not physically hooked up to ARM11. Thus, ARM11 cannot simply emulate ARM7.

What I'm interested in is a more in-depth explanation.

Nintendo obviously took the easy way out and just slapped an ARM7 on there, but I'm looking for clarification on the "hardware is not physically hooked up to ARM11" part. The 3DS hardware is basically the same as the DS hardware (at least, things like the the WiFi module, screens, microphone, etc). I don't know enough about the architecture of the 3DS to say which cores handle which pieces of hardware, but if *hax and homebrew can run solely on the ARM11, doesn't that mean the ARM11 has hardware access to the 3DS hardware regardless? So, why isn't it possible to directly execute ARM7 instructions from GBA roms or even DS roms on the ARM11, provided my assumption that the ARM11 has backwards compatibility with whatever instruction set the ARM7 runs (ARMv4T? ARMv3?) is correct.

(virtualise might be a better word than emulate)

dpad_5678 · Jan 17, 2016

I'm sure it can emulate it. Very shittely. With some coding, but it wont simply load the NDS files onto the TWL_NAND like it does when you boot an NDS cartridge. It will lag terribly nad will be pretty much unplayable.

3DBrew probably means emulation as in full speed which is impossible.

No one will try it though. I won't. You certainly won't. And since NDS flashcards are usually under $15 (at the most $35 for a SC DSTWO), I doubt it's worth anyone else's time.

chyyran · Jan 18, 2016

It says pretty specifically that ARM11 can not act as an ARM7 because some hardware isn't hooked up. AFAIK, the instruction set its backwards compatible, that is you should be able to directly execute ARM7 instructions on the ARM11. What I want to know is specifically what hardware the ARM11 doesn't have access to that prevents it from acting as a substitute ARM7. Even if I probably won't manage to write a VM for it myself, I'm curious as to why it's impractical, besides the fact that it's a lot of work for little payoff.

~Poke~ · Jan 18, 2016

Ron said:
It says pretty specifically that ARM11 can not act as an ARM7 because some hardware isn't hooked up. AFAIK, the instruction set its backwards compatible, that is you should be able to directly execute ARM7 instructions on the ARM11. What I want to know is specifically what hardware the ARM11 doesn't have access to that prevents it from acting as a substitute ARM7. Even if I probably won't manage to write a VM for it myself, I'm curious as to why it's impractical, besides the fact that it's a lot of work for little payoff.

I'm not an expert on this, but I do know that the ARM11 cpu doesn't have direct access to a lot of hardware (even things like reading from the SD card), and has to request it via the ARM9 kernel. That would interfere with any ARM9/7 code (at least, GBA/DS code) running directly on the ARM11 cpu since it would try to access things directly rather than request it.
That said, I wonder if this can be adjusted for, and if that would allow ARM7 code to run? Perhaps if they're very heavily patched, things like GBA games could run? (Fair warning, I don't know too much about this so I'm basically talking out of my ass here.)

nIxx · Jan 18, 2016

I think you should better ask this kind of questions in #3dsdev

tony_2018 · Jan 18, 2016

for realz.

the assaf · Jan 18, 2016

Same reason potato can't emulate ARN7.

Homebrew Specific reasons why ARM11 can not emulate ARM7?

somehow a weeb now.

Ape weak on own. Ape strong in unity.

somehow a weeb now.

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