View unanswered posts | View active topics It is currently Fri Dec 14, 2018 12:11 pm



Reply to topic  [ 4 posts ] 
 What is going on on ARM7 CPU? 
Author Message

Joined: Wed Aug 08, 2012 10:02 pm
Posts: 3
Hello,

I'm not sure whether this really belongs to libnds or devkitARM section, but I've recently restarted trying to code for the DS.

I have known for a while that the DS has two CPUs, one ARM7 and one ARM9, and that the ARM7 has less processing power and less hardware access (it seems to deal with the parts that already existed on the GBA).

What I didn't realize until a few hours ago is that we're advised against writing ARM7 in homebrews, but I don't really understand why.

Is it a libnds-related decision, so that all library services execute in parallel with the homebrew? Or is there some deep hardware reason that I missed?

If it's only libnds architecture, is there any documentation (other than the code) on what would break if I use my own ARM7 image? Or what precautions I should take when writing one? Or is it completely "proprietary" and ARM7 should just be considered as a static black box, just like the GPUs?

A secondary question, that I would understand being not answered, is if I give up the comfort of libnds, are there specific things that must be done on the ARM7 in my baremetal homebrew?

Just to be clear, I'm not questioning the architecture, I'm just trying to get a clear understanding of the limits, so I can play safely inside the box ("playing" here meaning at first porting a basic Ada runtime so I can code in my preferred language).

Thanks in advance for your help


Wed Oct 22, 2014 9:18 pm
Profile

Joined: Wed Aug 12, 2009 2:56 pm
Posts: 91
Location: github.com/sverx
The devkit provides a default program for the ARM7, and you can use that... you probably won't need to write a program for the ARM7 processor.
But, if you wish, it's possible... take a look into examples/nds/template, there's a 'combined' one which is for that.


Fri Oct 31, 2014 4:35 pm
Profile WWW

Joined: Thu Jul 02, 2009 1:19 pm
Posts: 352
audio, wifi, touchscreen, and some of the buttons can only be accessed from the arm7. These features are made accessible to arm9 by the FIFO IPC communications that are built into libnds. so the arm9 and arm7 code need to be kept in sync. The danger with developing for the arm7 is that you might break that communication. either directly or by releasing code that does not work in future versions of libnds.


Fri Oct 31, 2014 7:18 pm
Profile

Joined: Wed Aug 12, 2009 2:56 pm
Posts: 91
Location: github.com/sverx
Yeah, I was saying that it's very hard you really need to run a different ARM7 program than what's supplied with dkA/libnds... nevertheless you can have your own ARM7 program if you need it (ARM7 mp3 replay? libXM7? :roll: ...) using the so called 'combined' template.


Tue Nov 04, 2014 5:24 pm
Profile WWW
Display posts from previous:  Sort by  
Reply to topic   [ 4 posts ] 

Who is online

Users browsing this forum: No registered users and 4 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
  Powered by phpBB® Forum Software © phpBB Group
Designed by ST Software.
Get devkitPro at SourceForge.net. Fast, secure and Free Open Source software downloads