SNES PPU Warmup Period?

Discussion of hardware and software development for Super NES and Super Famicom. See the SNESdev wiki for more information.

Moderator: Moderators

Forum rules
  • For making cartridges of your Super NES games, see Reproduction.
Post Reply
User avatar
gravelstudios
Posts: 159
Joined: Mon Mar 13, 2017 5:21 pm
Contact:

SNES PPU Warmup Period?

Post by gravelstudios »

Does the SNES have a PPU warmup period like the NES, or is it ready to go as soon as the console is powered up?
User avatar
NovaSquirrel
Posts: 483
Joined: Fri Feb 27, 2009 2:35 pm
Location: Fort Wayne, Indiana
Contact:

Re: SNES PPU Warmup Period?

Post by NovaSquirrel »

You can write to SNES PPU registers immediately after powering on the console. I think the only hardware you actually have to wait for is the APU.
Pokun
Posts: 2681
Joined: Tue May 28, 2013 5:49 am
Location: Hokkaido, Japan

Re: SNES PPU Warmup Period?

Post by Pokun »

Yeah no warm-up needed, but initializing all the PPU and CPU registers (and clearing RAM, VRAM, CGRAM and OAM) takes some time as there are a lot of registers to write to (the official docs has a list of values to write to each register).

I guess the wait for the APU is waiting for the APU's IPL ROM to respond to your request which is what you do every time you upload code or data to it, so it's not only a warm-up time but part of the communication.
creaothceann
Posts: 611
Joined: Mon Jan 23, 2006 7:47 am
Location: Germany
Contact:

Re: SNES PPU Warmup Period?

Post by creaothceann »

The reset signal goes from the CIC to PPU2 and from there to the rest of the system, so the PPUs are probably the first components ready for operation.

Then the 5A22 may or may not perform some initialization before starting up its 65c816 core; we won't know without some oscilloscope measurements and/or interpreting die scans.

And lastly, the CPU performs its own RESET interrupt sequence before the programmer's code is executed.
My current setup:
Super Famicom ("2/1/3" SNS-CPU-GPM-02) → SCART → OSSC → StarTech USB3HDCAP → AmaRecTV 3.10
lidnariq
Posts: 11432
Joined: Sun Apr 13, 2008 11:12 am

Re: SNES PPU Warmup Period?

Post by lidnariq »

Pretty certain there's no external bus activity from the 5A22 separate from the 65816 after reset - it would have shown up on some of poot36's logic analyzer traces.
psycopathicteen
Posts: 3140
Joined: Wed May 19, 2010 6:12 pm

Re: SNES PPU Warmup Period?

Post by psycopathicteen »

Wait, the NES PPU had a warm up period?
Fiskbit
Posts: 891
Joined: Sat Nov 18, 2017 9:15 pm

Re: SNES PPU Warmup Period?

Post by Fiskbit »

See the second bullet point here.
creaothceann
Posts: 611
Joined: Mon Jan 23, 2006 7:47 am
Location: Germany
Contact:

Re: SNES PPU Warmup Period?

Post by creaothceann »

lidnariq wrote: Mon Mar 20, 2023 7:48 pm Pretty certain there's no external bus activity from the 5A22 separate from the 65816 after reset - it would have shown up on some of poot36's logic analyzer traces.
I meant internal initialization. We could in theory compare address/data bus recordings between a regular 65c816 and the 5A22 to see if the latter takes more time.
My current setup:
Super Famicom ("2/1/3" SNS-CPU-GPM-02) → SCART → OSSC → StarTech USB3HDCAP → AmaRecTV 3.10
Post Reply