Kickstart visible at f00000?

selco · 03 March 2015, 10:31

Hello,
I am trying to understand the booting of an Amiga and looked into the Kickstart-ROM. (A1200, 3.1ROM) Of course I have a compehension problem right at the beginning ;-)

At the very beginning it calculates a checksum and then does a

Code:

  
; this is address f800f2 in A1200 OS3.1

LEA    (START,PC),A0
LEA    ($F00000).L,A1
CMPA.L    A0,A1                ; What is compared here???
BEQ.B    .StartedFrom_f00000  ;we did start from f00000??? is that possible?
CMPI.W    #$1111,(A1)
BNE.B    .StartedFrom_f00000
JMP    (2,A1)                 ;f00000 begins with $1111. Jump ($f00002)

My question is, is the Kickstart also visible at f00000? Or when could that be the case?
I thought f00000 is Debug-ROM Space or FlashROM or used by 68060 cards?

Where does the Kickstart show up and under which circumstances/Amiga models?

Best regards

Toni Wilen · 03 March 2015, 11:53

CDTV and I think it was also used by development/prototype hardware.

mark_k · 04 March 2015, 20:21

I think the reason for Kickstart checking whether it's running from address $F00000 is in part due to Commodore's build process.

The memory at $F00000 was originally designed/intended for ROM cartridges. That's why Kickstart checks for a signature word at $F00000 ($1111) and jumps to $F00002 if found: it's calling the ROM cartridge code.

Commodore did provide builds of Kickstart assembled for address $F00000 to developers. With those, having code to check whether it's running at $F00000 makes sense; you can't call ROM cartridge code then. The check code was left in place for Kickstarts built for other addresses, though it isn't needed then.

[Probably various RAM boards for the A1000 and possibly also the 512KB CPU-slot RAM board in German-designed A2000s can be configured to appear at $F00000.]

plasmab · 29 October 2018, 14:10

It looks like it needs to match the tag at the start of your main ROM? Does that vary?

Actually no. I’m wrong.

jotd · 29 October 2018, 15:01

IIRC CD32 extended ROM is also located at F00000

There's also games checking for cartrdiges at F00000 (pinball dreams).

plasmab · 29 October 2018, 15:02

Quote:

Originally Posted by jotd

IIRC CD32 extended ROM is also located at F00000

There's also games checking for cartrdiges at F00000 (pinball dreams).

Yeah I just misread the code

MartinW · 28 December 2018, 14:23

The custom made "GB A1000" has flash memory mapped at 0x00F00000 that does exactly this. It starts with $1111 and then has code which performs early startup code to configure 32bit memory space, plays a startup animation and then proceeds to kickstart at 0x00F80000.

[EDIT] Oops, sorry, just realised I'm posting to an old thread

03 March 2015, 10:31	#1
selco Registered User Join Date: Aug 2013 Location: Germany Posts: 81	Kickstart visible at f00000? Hello, I am trying to understand the booting of an Amiga and looked into the Kickstart-ROM. (A1200, 3.1ROM) Of course I have a compehension problem right at the beginning ;-) At the very beginning it calculates a checksum and then does a Code: ; this is address f800f2 in A1200 OS3.1 LEA (START,PC),A0 LEA ($F00000).L,A1 CMPA.L A0,A1 ; What is compared here??? BEQ.B .StartedFrom_f00000 ;we did start from f00000??? is that possible? CMPI.W #$1111,(A1) BNE.B .StartedFrom_f00000 JMP (2,A1) ;f00000 begins with $1111. Jump ($f00002) My question is, is the Kickstart also visible at f00000? Or when could that be the case? I thought f00000 is Debug-ROM Space or FlashROM or used by 68060 cards? Where does the Kickstart show up and under which circumstances/Amiga models? Best regards

29 October 2018, 14:10	#4
plasmab Banned Join Date: Sep 2016 Location: UK Posts: 2,917	Kickstart visible at f00000? It looks like it needs to match the tag at the start of your main ROM? Does that vary? Actually no. I’m wrong.

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03 March 2015, 11:53	#2
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 49 Posts: 26,502	CDTV and I think it was also used by development/prototype hardware.

04 March 2015, 20:21	#3
mark_k Registered User Join Date: Aug 2004 Location: Posts: 3,333	I think the reason for Kickstart checking whether it's running from address $F00000 is in part due to Commodore's build process. The memory at $F00000 was originally designed/intended for ROM cartridges. That's why Kickstart checks for a signature word at $F00000 ($1111) and jumps to $F00002 if found: it's calling the ROM cartridge code. Commodore did provide builds of Kickstart assembled for address $F00000 to developers. With those, having code to check whether it's running at $F00000 makes sense; you can't call ROM cartridge code then. The check code was left in place for Kickstarts built for other addresses, though it isn't needed then. [Probably various RAM boards for the A1000 and possibly also the 512KB CPU-slot RAM board in German-designed A2000s can be configured to appear at $F00000.]

29 October 2018, 15:01	#5
jotd This cat is no more Join Date: Dec 2004 Location: FRANCE Age: 52 Posts: 8,161	IIRC CD32 extended ROM is also located at F00000 There's also games checking for cartrdiges at F00000 (pinball dreams).

28 December 2018, 14:23	#7
MartinW Registered User Join Date: Mar 2017 Location: Minehead / UK Posts: 608	The custom made "GB A1000" has flash memory mapped at 0x00F00000 that does exactly this. It starts with $1111 and then has code which performs early startup code to configure 32bit memory space, plays a startup animation and then proceeds to kickstart at 0x00F80000. [EDIT] Oops, sorry, just realised I'm posting to an old thread

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